OsNAC121 regulates root development, tillering, panicle morphology, and grain filling in rice plant.

Transcription factors in coordination with phytohormones form an intricate regulatory network modulating vital cellular mechanisms like development, growth and senescence in plants. In this study, we have functionally characterized the transcription factor OsNAC121 by developing gene silencing and overexpressing transgenic rice plants, followed by detailed analyses of the plant architecture. Transgenic lines exhibited remodelling in crown root development, lateral root structure and density, tiller height and number, panicle and grain morphologies, underpinning the imbalanced auxin: cytokinin ratio due to perturbed auxin transportation. Application of cytokinin, auxin and abscisic acid increased OsNAC121 gene expression nearly 17-, 6- and 91-folds, respectively. qRT-PCR results showed differential expressions of auxin and cytokinin pathway genes, implying their altered levels. A 47-fold higher expression level of OsNAC121 during milky stage in untransformed rice, compared to 14-day old shoot tissue, suggests its crucial role in grain filling; as evidenced by a large number of undeveloped grains produced by the gene silenced lines. Crippled gravitropic response by the transgenic plants indicates their impaired auxin transport. Bioinformatics revealed that OsNAC121 interacts with co-repressor (TOPLESS) proteins and forms a part of the inhibitor complex OsIAA10, an essential core component of auxin signalling pathway. Therefore, OsNAC121 emerges as an important regulator of various aspects of plant architecture through modulation of crosstalk between auxin and cytokinin, altering their concentration gradient in the meristematic zones, and consequently modifying different plant organogenesis processes.

Rice Big Grain1 improves grain yield in ectopically expressing rice and heterologously expressing tobacco plants.

Functional genomics through transgenesis has provided faster and more reliable methods for identifying, characterizing, and utilizing genes or quantitative trait loci linked to agronomic traits to target yield. The present study explored the role of Big Grain1 (BG1) gene of rice (Oryza sativa L.) in yield improvement of crop plants. We aimed to identify the genetic variation of OsBG1 in various indica rice cultivars by studying the allelic polymorphism of the gene, while also investigating the gene's potential to increase crop yield through the transgenic approach. Our study reports the presence of an extra 393 bp sequence having two 6 bp enhancer elements in the 3' regulatory sequence of OsBG1 in the large-grain cultivar IR64 but not in the small-grain cultivar Badshahbhog. A single copy of the OsBG1 gene in both the cultivars and a 4.1-fold higher expression of OsBG1 in IR64 than in Badshahbhog imply that the grain size is positively correlated with the level of OsBG1 expression in rice. The ectopic expression of OsBG1 under the endosperm-specific glutelin C promoter in Badshahbhog enhanced the flag leaf length, panicle weight, and panicle length by an average of 33.2%, 33.7%, and 30.5%, respectively. The length of anthers, spikelet fertility, and grain yield per plant increased in transgenic rice lines by an average of 27.5%, 8.3%, and 54.4%, respectively. Heterologous expression of OsBG1 under the constitutive 2xCaMV35S promoter improved the number of seed pods per plant and seed yield per plant in transgenic tobacco lines by an average of 2.2-fold and 2.6-fold, respectively. Improving crop yield is crucial to ensure food security and socio-economic stability, and identifying suitable genetic factor is the essential step towards this endeavor. Our findings suggest that the OsBG1 gene is a promising candidate for improving the grain yield of monocot and dicot plant systems by molecular breeding and genetic engineering.

Rice Big Grain1 enhances biomass and plant growth-promoting traits in rhizospheric yeast Candida tropicalis.

The Big Grain1 (BG1) gene of rice (Oryza sativa L.) is reported to increase the yield of rice crops; however, its molecular mechanism is largely concealed. To explore its functional prospects, we have taken a structure-function-based approach. In silico analyses suggest OsBG1 is a DNA- and phytohormone-binding protein. Heterologous expression of OsBG1 with galactose-inducible promoter GAL1p in the rhizospheric yeast Candida tropicalis SY005 revealed 7.9- and 1.5-fold higher expression of the gene at 12 and 24 h, respectively, compared to the expression at 36 h post-galactose induction. Functional activity of the induced OsBG1 in engineered yeast increased cell density, specific growth rate, and biomass by 28.5%, 29.8%, and 14.1%, respectively, and decreased the generation time by 21.25%. Flow cytometry-based cell cycle analysis of OsBG1-expressing yeast cells exhibited an increase in the cells of the G2/M population by 15.8% after 12 h of post-galactose induction. The gene expression study of yeast transformants disclosed that OsBG1 regulates cell division by upregulating the expression of the endogenous gene cyclin B1 (CtCYB1) by 1.3- and 1.9-folds at 10 and 12 h, respectively, compared to the control, and is positively influenced by the phytohormone indole acetic acid (IAA). Further, the study revealed that OsBG1 significantly increases biofilm formation, stress tolerance, and IAA production in C. tropicalis SY005, implying its prospective role in enhancing plant growth-promoting traits in microbes. OsBG1-expressing rhizospheric yeast cells significantly improved the germination and growth parameters of the bio-inoculated rice seeds. Altogether, this study suggests OsBG1 can be employed to genetically improve suitable bio-inoculants for their plant growth-promoting traits to augment crop productivity. KEY POINTS: • In silico analyses suggested OsBG1 is a phytohormone-binding transcription factor. • OsBG1 enhanced growth in rhizospheric Candida tropicalis by upregulating CtCYB1. • OsBG1 improved plant growth-promoting traits of the rhizospheric yeast C. tropicalis.

Lipid-rich endo-metabolites from a vertically transmitted fungal endophyte Penicillium sp. PM031 attenuate virulence factors of phytopathogenic Ralstonia solanacearum.

The bacterial wilt caused by Ralstonia solanacearum is a destructive plant disease globally. Since a completely non-biological control measure could be a matter of environmental concern, investigations of developing eco-friendly strategies are required to control this phytopathogen. Attenuation of the bacterial virulence in addition to destroying the pathogen may be an alternative and overarching approach to control this disease. In this study, we have explored the potentiality of a vertically transmitted endophytic fungus Penicillium sp. PM031 isolated from stem of in vitro grown, wilt susceptible tomato cultivar to control this phytopathogen. The endophytic fungus was unable to inhibit the bacterial growth during direct confrontation in co-culture system; rather its growth and extracellular secretion were affected by the bacterium. Interestingly, the PM031-derived endo-metabolites, containing ~80% of lipid molecules, showed the dose-dependent growth inhibitory effect against R. solanacearum. Metabolite treatment with a concentration of 2500 and 5000 µg/ml significantly inhibited the bacterial growth 24.72% and 64.31%, respectively. Higher concentrations of endo-metabolite treatment exhibited antibacterial activity by rupturing cellular membranes. Furthermore, the endo-metabolites negatively influence the virulence factors necessary in early phases of bacterial infection, such as motility and biofilm formation. Our study highlights even if an endophytic fungus associated with the susceptible host plant cannot tackle R. solanacearum directly, its lipid-rich metabolites have potential to attenuate the virulence of phytopathogen. We believe this study can be a stepping stone to develop suitable formulations to control the bacterial wilt in a sustainable way, which will reduce excessive uses of synthetic bactericides.

Characterization of an alcohol acetyltransferase GcAAT responsible for the production of antifungal volatile esters in endophytic Geotrichum candidum PF005.

Alcohol acetyltransferases (AATs) are a group of enzymes that catalyze the formation of esters from different alcohols and acetyl-CoA. However, these enzymes are not well characterized with regard to synthesis of antifungal compounds. The present study aims to investigate the AAT enzyme from Geotrichum candidum PF005, an endophytic yeast-like fungus that emits fruity scented antifungal volatiles, primarily comprising of acetate esters. After PCR-based cloning of the GcAAT gene, the encoded enzyme was characterized structurally through in silico methods and functionally via heterologous expression in Saccharomyces cerevisiae. In native host, the single copy GcAAT gene exhibited induced expression upon supplementation with metabolic precursors, like L-leucine (Leu) or α-ketoisocaproate (α-KIC). Docking studies using the modelled structure of GcAAT revealed differential but favourable binding interactions for three alcohol substrates (i.e., isoamyl alcohol, isobutyl alcohol and 2-phenylethanol) and the co-substrate acetyl-CoA. Binding sites for both substrate and co-substrate are found to be located inside a tunnel identified in the structure, wherein the H208 of the acetyltransferase conserved motif HXXXD was found at a hydrogen bond distance from the substrate. Functional complementation of GcAAT in S. cerevisiae AAT knockout strain caused 32% decrease in dry biomass weight of the test phytopathogenic fungus, Rhizoctonia solani as compared to the control (AAT knockout strain with empty plasmid) after 72 h of incubation due to the emitted volatiles. When the transformed yeast cells were fed with Leu and α-KIC, the relative abundance of the isoamyl acetate ester increased by 21% and 48%, respectively as compared to the control (without precursor). Further analysis documented that volatiles from α-KIC fed GcAAT transformant exhibited 58% higher antifungal activity against the test fungus R. solani than the control, engendered by increased oxidative stress that led to distorted mycelial morphology and increased hyphal branching. Together, the augmented antifungal effect displayed by the GcAAT expressing S. cerevisiae AAT knockout strain is clearly attributable to the acetate esters, especially isoamyl acetate, which are inherently produced in endophytic G. candidum PF005 as antifungal volatiles.

TypiCal but DeliCate Ca++re: Dissecting the Essence of Calcium Signaling Network as a Robust Response Coordinator of Versatile Abiotic and Biotic Stimuli in Plants.

Plant growth, development, and ultimately crop productivity are largely impacted by the interaction of plants with different abiotic and biotic factors throughout their life cycle. Perception of different abiotic stresses, such as salt, cold, drought, heat, and heavy metals, and interaction with beneficial and harmful biotic agents by plants lead to transient, sustained, or oscillatory changes of [calcium ion, Ca2+]cyt within the cell. Significant progress has been made in the decoding of Ca2+ signatures into downstream responses to modulate differential developmental and physiological responses in the whole plant. Ca2+ sensor proteins, mainly calmodulins (CaMs), calmodulin-like proteins (CMLs), and others, such as Ca2+-dependent protein kinases (CDPKs), calcineurin B-like proteins (CBLs), and calmodulin-binding transcription activators (CAMTAs) have played critical roles in coupling the specific stress stimulus with an appropriate response. This review summarizes the current understanding of the Ca2+ influx and efflux system in plant cells and various Ca2+ binding protein-mediated signal transduction pathways that are delicately orchestrated to mitigate abiotic and biotic stresses. The probable interactions of different components of Ca2+ sensor relays and Ca2+ sensor responders in response to various external stimuli have been described diagrammatically focusing on established pathways and latest developments. Present comprehensive insight into key components of the Ca2+ signaling toolkit in plants can provide an innovative framework for biotechnological manipulations toward crop improvability in near future.

Lipid production by oleaginous yeasts.

Microbial lipid production has been studied extensively for years; however, lipid metabolic engineering in many of the extraordinarily high lipid-accumulating yeasts was impeded by inadequate understanding of the metabolic pathways including regulatory mechanisms defining their oleaginicity and the limited genetic tools available. The aim of this review is to highlight the prominent oleaginous yeast genera, emphasizing their oleaginous characteristics, in conjunction with diverse other features such as cheap carbon source utilization, withstanding the effect of inhibitory compounds, commercially favorable fatty acid composition-all supporting their future development as economically viable lipid feedstock. The unique aspects of metabolism attributing to their oleaginicity are accentuated in the pretext of outlining the various strategies successfully implemented to improve the production of lipid and lipid-derived metabolites. A large number of in silico data generated on the lipid accumulation in certain oleaginous yeasts have been carefully curated, as suggestive evidences in line with the exceptional oleaginicity of these organisms. The different genetic elements developed in these yeasts to execute such strategies have been scrupulously inspected, underlining the major types of newly-found and synthetically constructed promoters, transcription terminators, and selection markers. Additionally, there is a plethora of advanced genetic toolboxes and techniques described, which have been successfully used in oleaginous yeasts in the recent years, promoting homologous recombination, genome editing, DNA assembly, and transformation at remarkable efficiencies. They can accelerate and effectively guide the rational designing of system-wide metabolic engineering approaches pinpointing the key targets for developing industrially suitable yeast strains.

Yeasts of the Blastobotrys genus are promising platform for lipid-based fuels and oleochemicals production.

Strains of the yeast genus Blastobotrys (subphylum Saccharomycotina) represent a valuable biotechnological resource for basic biochemistry research, single-cell protein, and heterologous protein production processes. Species of this genus are dimorphic, non-pathogenic, thermotolerant, and can assimilate a variety of hydrophilic and hydrophobic substrates. These can constitute a single-cell oil platform in an emerging bio-based economy as oleaginous traits have been discovered recently. However, the regulatory network of lipogenesis in these yeasts is poorly understood. To keep pace with the growing market demands for lipid-derived products, it is critical to understand the lipid biosynthesis in these unconventional yeasts to pinpoint what governs the preferential channelling of carbon flux into lipids instead of the competing pathways. This review summarizes information relevant to the regulation of lipid metabolic pathways and prospects of metabolic engineering in Blastobotrys yeasts for their application in food, feed, and beyond, particularly for fatty acid-based fuels and oleochemicals. KEY POINTS: • The production of biolipids by heterotrophic yeasts is reviewed. • Summary of information concerning lipid metabolism regulation is highlighted. • Special focus on the importance of diacylglycerol acyltransferases encoding genes in improving lipid production is made.

Metagenomics of two gnotobiotically grown aromatic rice cultivars reveals genotype-dependent and tissue-specific colonization of endophytic bacterial communities attributing multiple plant growth promoting traits.

Exploration of community structures, habitations, and potential plant growth promoting (PGP) attributes of endophytic bacteria through next generation sequencing (NGS) is a prerequisite to culturing PGP endophytic bacteria for their application in sustainable agriculture. The present study unravels the taxonomic abundance and diversity of endophytic bacteria inhabiting in vitro grown root, shoot and callus tissues of two aromatic rice cultivars through 16S rRNA gene-based Illumina NGS. Wide variability in the number of bacterial operational taxonomic units (OTUs) and genera was observed between the two samples of the root (55, 14 vs. 310, 76) and shoot (26, 12 vs. 276, 73) but not between the two callus samples (251, 61 vs. 259, 51), indicating tissue-specific and genotype-dependent bacterial community distribution in rice plant, even under similar gnotobiotic growth conditions. Sizes of core bacteriomes of the selected two rice genotypes varied from 1 to 15 genera, with Sphingomonas being the only genus detected in all six samples. Functional annotation, based upon the abundance of bacterial OTUs, revealed the presence of several PGP trait-related genes having variable relative abundance in tissue-specific and genotype-dependent manners. In silico study also documented a higher abundance of certain genes in the same biochemical pathway, such as nitrogen fixation, phosphate solubilization and indole acetic acid production; implying their crucial roles in the biosynthesis of metabolites leading to PGP. New insights on utilizing callus cultures for isolation of PGP endophytes aiming to improve rice crop productivity are presented, owing to constancy in bacterial OTUs and genera in callus tissues of both the rice genotypes.

Recent advances in lipid metabolic engineering of oleaginous yeasts.

With the increasing demand to develop a renewable and sustainable biolipid feedstock, several species of non-conventional oleaginous yeasts are being explored. Apart from the platform oleaginous yeast Yarrowia lipolytica, the understanding of metabolic pathway and, therefore, exploiting the engineering prospects of most of the oleaginous species are still in infancy. However, in the past few years, enormous efforts have been invested in Rhodotorula, Rhodosporidium, Lipomyces, Trichosporon, and Candida genera of yeasts among others, with the rapid advancement of engineering strategies, significant improvement in genetic tools and techniques, generation of extensive bioinformatics and omics data. In this review, we have collated these recent progresses to make a detailed and insightful summary of the major developments in metabolic engineering of the prominent oleaginous yeast species. Such a comprehensive overview would be a useful resource for future strain improvement and metabolic engineering studies for enhanced production of lipid and lipid-derived chemicals in oleaginous yeasts.

Characterization of two sugar transporters responsible for efficient xylose uptake in an oleaginous yeast Candida tropicalis SY005.

Microbial conversion of lignocellulosic feedstock to the target bioproduct requires efficient assimilation of its constituent sugars, a large part of which comprises of glucose and xylose. This study aims to identify and characterize sugar transporters capable of xylose uptake in an oleaginous strain of the industrially relevant yeast Candida tropicalis. In silico database mining resulted in two sugar transporter proteins- CtStp1 and CtStp2, containing conserved amino acid residues and motifs that have been previously reported to be involved in xylose transport in other organisms. Several softwares predicted the likelihood of 10-12 transmembrane (TM) helices to be present in both the Stps, while molecular modelling showed 12 TM helices that were organized into a typical structure found in the major facilitator superfamily of transporters. Docking with different sugars also predicted favorable interactions. Heterologous expression in a Saccharomyces cerevisiae strain harboring functional xylose metabolic genes validated the broad substrate specificity of the two Stps. Each transporter supported prominent growth of recombinant S. cerevisiae strains on six sugars including xylose at various concentrations. Expression of CtSTP1 and CtSTP2 along with the xylose metabolic genes in yeast transformants grown in presence of xylose was confirmed by transcript detection. Growth curve and sugar consumption profiles revealed uptake of both glucose and xylose simultaneously by the recombinant yeast strains, though CtStp1 showed relatively less effect of glucose repression in mixed sugars and was a better transporter of xylose than CtStp2. Such glucose-xylose utilizing efficient transporters can be effective tools for developing co-fermenting yeasts through genetic engineering in future, with noteworthy applications in renewable biomass utilization.

Impact of seed-transmitted endophytic bacteria on intra- and inter-cultivar plant growth promotion modulated by certain sets of metabolites in rice crop.

Exploring the beneficial interactions between plant and endophytes could be an effective strategy in the implementation of sustainable agricultural practices to enhance crop productivity. In this study, we aimed to evaluate holistically the plant growth promoting (PGP) abilities rendered by seed-transmitted endophytic bacteria isolated from in vitro grown calli of two rice cultivars. Nine bacterial endophytes, designated as PB001-PB009, were isolated and identified at the genus level through 16S rRNA gene sequence analysis. Biochemical investigations disclosed that they possess several PGP traits, such as phosphate solubilization, indole acetic acid biosynthesis, ammonia production, nitrogen fixation, amylase production and siderophore production. Results in gnotobiotic conditions revealed an increase in fresh weight, dry weight, root length and shoot length of seedlings germinated from endophyte-primed seeds than the control (uninoculated) set in a non-host and two host rice cultivars. In net house experiments, plants germinated from Micrococcus sp. PB001, Pseudomonas sp. PB002, Methylobacterium sp. PB005 and Methylorubrum sp. PB009 primed seeds showed an increase of upto 34.06 %, 38.77 %, 182.87 %, 16.59 % and 33.52 % in chlorophyll content, number of tillers/plant, number of grains/plant, grain size and grain weight, respectively than control plant sets in the non-host rice cultivar, further validating inter-cultivar PGP abilities of these endophytes. Metabolite profiling unfolded the abundance of few metabolites that are involved in pathways associated with PGP traits, in seedlings germinated from the endophyte-primed seeds. Together, the study documents the effect of seed-transmitted endophytic bacteria on intra- and inter-cultivar PGP by modulating certain sets of metabolites in rice plant, and is promising in developing bioinoculant formulations employing these selected endophytes for enhancement of rice productivity.

Engineering an oleaginous yeast Candida tropicalis SY005 for enhanced lipid production.

Candida tropicalis has recently emerged as a valuable yeast species with respect to lipid metabolism, not only for its oleaginous characteristics but also for its ability to utilize diverse range of substrates. Hence, it can be explored as an ideal host for lipid metabolic engineering, although inadequate genetic transformation system for developing the stable transformant has limited this scope. To resolve this existing constraint, we have come up with a novel strategy of a genomic integrating system in the oleaginous strain SY005 of C. tropicalis. Employing this system, comprising of host-specific regulatable promoter, transcription terminator, and integration locus, we have first examined the expression of a reporter gene, and then ectopically expressed a transcription factor CtRAP1 encoding the repressor activator protein 1 of C. tropicalis SY005. A maximum lipid content of 0.37 g/g dry cell weight was achieved in the engineered strain upon galactose induction, leading to 60% (w/w) increase relative to the wild type strain SY005. This work demonstrates the use of a markerless integrative transformation system to promote lipid accumulation in the diploid yeast without applying nutrient stress and hampering cell growth. The findings of this study will augment the research on lipid metabolic engineering and exploit the enormous potential of C. tropicalis as an industrial lipid feedstock. Key points •A transformation system was established in oleaginous yeast Candida tropicalis SY005 •Activity of host-specific molecular elements was verified by reporter gene expression •SY005 was engineered to ectopically express a transcriptional regulator gene CtRAP1 •The engineered strain exhibited 60% increase in lipid content on galactose induction •The increase in lipid content was correlated with the induced expression of CtRAP1.

Identification and functional characterization of a lipid droplet protein CtLDP1 from an oleaginous yeast Candida tropicalis SY005.

Proteins residing in lipid droplets (LDs) of organisms exhibit diverse physiological roles. Since the LD proteins of yeasts are largely unexplored, we have identified a putative LD protein gene, CtLDP1 in the oleaginous yeast Candida tropicalis SY005 and characterized its function. The increased lipid accumulation in SY005 could be correlated with enhanced (~2.67-fold) expression of the CtLDP1 after low-nitrogen stress. The N-terminal transmembrane domain similar to perilipin proteins and the amphipathic α-helices predicted in silico, presumably aid in targeting the CtLDP1 to LD membranes. Heterologous expression of CtLDP1-mCherry fusion in Saccharomyces cerevisiae revealed localization in LDs, yet the expression of CtLDP1 did not show significant effect on LD formation in transformed cells. Molecular docking showed favourable interactions of the protein with sterol class of molecules, but not with triacylglycerol (TAG); and this was further experimentally verified by co-localization of the mCherry-tagged protein in TAG-deficient (but steryl ester containing) LDs. While oleic acid supplementation caused coalescence of LDs into supersized ones (average diameter = 1.19 ± 0.12 µm; n = 160), this effect was suppressed due to CtLDP1 expression, and the cells mostly exhibited numerous smaller LDs (average diameter = 0.46 ± 0.05 µm; n = 160). Moreover, CtLDP1 expression in pet10Δ knockout strain of S. cerevisiae restored multiple LD formation, indicating functional complementation of the protein. Overall, this study documents functional characterization of an LD-stabilizing protein from an oleaginous strain of Candida genus for the first time, and provides insights on the characteristics of LD proteins in oleaginous yeasts for future metabolic engineering.

Efficient xylose utilization leads to highest lipid productivity in Candida tropicalis SY005 among six yeast strains grown in mixed sugar medium.

Six local isolates of yeasts were screened for cell mass and lipid production in mixed glucose and xylose medium. Candida tropicalis SY005 and Trichosporon (Apiotrichum) loubieri SY006 showed significant lipid accumulation of 24.6% and 32% (dry cell weight), respectively when grown in medium containing equal mass of both the sugars. SY005 produced relatively higher cell mass of 9.66 gL-1 due to higher rate of sugar consumption, which raised the lipid productivity of the organism to 0.792 gL-1day-1 as compared to 0.446 gL-1day-1 in SY006. When grown with each sugar separately, the xylose consumption rate of SY005 was found to be 0.55 gL-1 h-1 after 4 days as compared to 0.52 gL-1 h-1 for SY006. Transcript expression of the high affinity xylose transporter (Cthaxt), xylose reductase (Ctxyl1), and xylitol dehydrogenase (Ctxyl2) of SY005 was monitored to unravel such high rate of sugar consumption. Expression of all the three genes was observed to vary in mixed sugars with Cthaxt exhibiting the highest expression in presence of only xylose. Expression levels of both Ctxyl1 and Ctxyl2, involved in xylose catabolism, were maximum during 24-48 h of growth, indicating that xylose utilization started in the presence of glucose, which was depleted in the medium after 96 h. Together, the present study documents that C. tropicalis SY005 consumes xylose concomitant to glucose during early period of growth, and it is a promising yeast strain for viable production of storage lipid or other high-value oleochemicals utilizing lignocellulose hydrolysate.

Expression of rice MATE family transporter OsMATE2 modulates arsenic accumulation in tobacco and rice.

KEY MESSAGE: The OsMATE2 upon constitutive expression in tobacco decreases root-to-shoot As transfer coefficient and its endosperm-specific silencing in rice reduces grain As content, broadening the role of MATE proteins in planta. Rice (Oryza sativa) is capable of accumulating significant amount of arsenic (As) in grains, causing serious health hazard for rice consuming population. The multidrug and toxic compound extrusion (MATE) protein family comprises a large group of secondary transporters present universally in living organisms, and transports metabolites and/or xenobiotic compounds. OsMATE2, one of the MATE family members of rice was found to be transcriptionally up-regulated (sixfolds) in the developing seeds during As stress, and showed positive correlation with the As content in mature grains. Therefore, to understand the role of OsMATE2 in As accumulation, constitutive expression in tobacco was carried out. Transgenic tobacco plants exhibited decreased root-to-shoot As transfer coefficient (33.3-39.6%) along with augmented As sensitivity by increasing oxidative stress compared to untransformed control plants, indicating the involvement of OsMATE2 in As accumulation. Consequently, RNAi strategy was utilized for endosperm-specific silencing of endogenous OsMATE2 to mitigate As accumulation in rice grains. Transgenic rice lines demonstrated significant reduction of both OsMATE2 transcript (~ 38-87%) and grain As content (36.9-47.8%) compared to the control plants without undesirable effects on agronomical traits. Together, the present findings indicate the connection of OsMATE2 in As accumulation, and could expand the functional role of MATE proteins in planta.

Effect of elevated [CO2 ] on yield, intra-plant nutrient dynamics, and grain quality of rice cultivars in eastern India.

BACKGROUND: Climate models predict an increase in global temperature in response to a doubling of atmospheric [CO2 ]. This may affect future rice production and quality. In this study, the effect of elevated [CO2 ] on yield, nutrient acquisition and utilization, and grain quality of rice genotypes was investigated in the subtropical climate of eastern India (Kharagpur). Three environments (open field, ambient, and elevated [CO2 ]) were tested using four rice cultivars of eastern India. RESULTS: Under elevated [CO2 ] (25% higher), the yield of high-yielding cultivars (HYCs) viz IR 36, Swarna, and Swarna sub1 was significantly reduced (by 11-13%), whereas the yield increased (by 6-9%) for Badshabhog, a low-yielding aromatic cultivar. Elevated [CO2 ] significantly enhanced K uptake (by 14-21%), but did not influence the uptake of total N and P. The nutrient harvest index and use efficiency values in HYCs were reduced under elevated [CO2 ] indicating that nutrient translocation from source to sink (grain) was significantly reduced. An increase in alkali spreading value (10%) and reduction in grain protein (2-3%) and iron (5-6%) was also observed upon [CO2 ] elevation. CONCLUSION: The study highlights the importance of nutrient management (increasing N rate for HYCs) and selective breeding of tolerant cultivars in minimizing the adverse effects of elevated [CO2 ] on rice yield and quality. © 2018 Society of Chemical Industry.

Rice matrix metalloproteinase OsMMP1 plays pleiotropic roles in plant development and symplastic-apoplastic transport by modulating cellulose and callose depositions.

Matrix metalloproteinases (MMPs) are well-known proteolytic enzymes in animal systems and play roles in tissue differentiation, growth, and defence. Although a few plant MMPs have been reported, their exact functions in development and growth remain elusive. In this study, we characterized the promoter and coding sequence of OsMMP1, one of the putative MMP genes in rice (Oryza sativa). The OsMMP1 catalytic domain is structurally similar to human MMPs with respect to cofactor orientation as predicted by homology modeling. Bacterially expressed recombinant OsMMP1 showed protease activity with bovine serum albumin and gelatin as substrates. Analyses of transcript accumulation and promoter-reporter gene expression revealed that OsMMP1 is spatio-temporally expressed in vegetative and reproductive parts of plants. The plasma membrane-localized OsMMP1 protease affected plant development upon heterologous expression in tobacco and endogenous gene silencing in rice. Transgenic tobacco plants expressing OsMMP1 showed enhanced deposition of cellulose and callose, leading to impairment of symplastic and apoplastic translocations. Moreover, transgenic tobacco tissues exhibited tolerance to oxidative stress-inducing agent by confining the area of tissue death owing to callose lining. Collectively, these findings demonstrate the involvement of a plant MMP in growth, organ differentiation, and development in relation to cell wall modification.

Quorum sensing inhibitors: can endophytes be prospective sources?

Endophytes are microbes which reside inside the plant tissues asymptomatically or causing pathogenicity to the host plant for a brief period. Owing to their presence in a specialized niche, endophytes are capable of synthesizing diverse types of bioactive molecules. Continuous development of resistance mechanism by pathogens to the currently available health treatments and pharmaceuticals has led researchers to explore new therapeutic agents. Quorum sensing has a role in the development of microbial pathogenic traits including biofilm formation. Utilization of quorum sensing (QS) inhibitors in antivirulence approach against pathogenesis is one of the innovative strategies. Endophytic microbes provide a plethora of such required bioactive molecules. This review summarizes the bioprospecting of endophytic microbes for production of novel QS inhibitors. At the outset, an overview is presented about the QS and QS inhibition followed by a summary on the endophytes as a treasure trove of bioactive metabolites, particularly the QS inhibitors. Next, we have outlined screening, purification, production, and application of QS inhibitors starting from the isolation of endophytic microbes. There is huge prospect for endophytes in the domain of human healthcare and food industry, provided that we develop a comprehensive understanding of the biology of endophyte and its ecosystem.

Characterization and Synergistic Effect of Antifungal Volatile Organic Compounds Emitted by the Geotrichum candidum PF005, an Endophytic Fungus from the Eggplant.

Plant-associated endophytes are recognized as sources of novel bioactive molecules having diverse applications. In this study, an endophytic yeast-like fungal strain was isolated from the fruit of eggplant (Solanum melongena) and identified as Geotrichum candidum through phenotypic and genotypic characterizations. This endophytic G. candidum isolate PF005 was found to emit fruity scented volatiles. The compositional profiling of volatile organic compounds (VOCs) revealed the presence of 3-methyl-1-butanol, ethyl 3-methylbutanoate, 2-phenylethanol, isopentyl acetate, naphthalene, and isobutyl acetate in significant proportion when analyzed on a time-course basis. The VOCs from G. candidum exhibited significant mycelial growth inhibition (54%) of phytopathogen Rhizoctonia solani, besides having mild antifungal activity against a few other fungi. The source of carbon as a nutrient was found to be an important factor for the enhanced biosynthesis of antifungal VOCs. The antifungal activity against phytopathogen R. solani was improved up to 91% by feeding the G. candidum with selective precursors of alcohol and ester volatiles. Furthermore, the antifungal activity of VOCs was enhanced synergistically up to 92% upon the exogenous addition of naphthalene (1.0 mg/plate). This is the first report of G. candidum as an endophyte emitting antifungal VOCs, wherein 2-penylethanol, isopentyl acetate, and naphthalene were identified as important contributors to its antifungal activity. Possible utilization of G. candidum PF005 as a mycofumigant has been discussed based upon its antifungal activity and the qualified presumption of safety status.