Multi-Population Analysis for Leaf and Neck Blast Reveals Novel Source of Neck Blast Resistance in Rice.

Rice blast is one of the most devastating biotic stresses that limits rice productivity. The North Eastern Hill (NEH) region of India is considered to be one of the primary centres of diversity for both rice and pathotypes of Magnaporthe grisea. Therefore, the present study was carried out to elucidate the genetic basis of leaf and neck blast resistance under Meghalaya conditions. A set of 80 diverse genotypes (natural population) and 2 F2 populations involving resistant parent, a wildtype landrace, LR 5 (Lal Jangali) and susceptible genotypes Sambha Mahsuri SUB 1 (SMS) and LR 26 (Chakhao Poireiton) were used for association analysis of reported major gene-linked markers with leaf and neck blast resistance to identify major effective genes under local conditions. Genotyping using twenty-five gene-specific markers across diverse genotypes and F2 progenies revealed genes Pi5 and Pi54 to be associated with leaf blast resistance in all three populations. Genes Pib and qPbm showed an association with neck blast resistance in both natural and LR 5 × SMS populations. Additionally, a set of 184 genome-wide polymorphic markers (SSRs and SNPs), when applied to F2-resistant and F2-susceptible DNA bulks derived from LR 5 × LR 26, suggested that Pi20(t) on chromosome 12 is one of the major genes imparting disease resistance. Markers snpOS318, RM1337 and RM7102 and RM247 and snpOS316 were associated with leaf blast and neck blast resistance, respectively. The genotypes, markers and genes will help in marker-assisted selection and development of varieties with durable resistance.

Genome-wide identification and expression profiling of growth­regulating factor (GRF) and GRF­interacting factor (GIF) gene families in chickpea and pigeonpea.

The growth-regulating factor (GRF) and GRF-interacting factor (GIF) families encode plant-specific transcription factors and play vital roles in plant development and stress response processes. Although GRF and GIF genes have been identified in various plant species, there have been no reports of the analysis and identification of the GRF and GIF transcription factor families in chickpea (Cicer arietinum) and pigeonpea (Cajanus cajan). The present study identified seven CaGRFs, eleven CcGRFs, four CaGIFs, and four CcGIFs. The identified proteins were grouped into eight and three clades for GRFs and GIFs, respectively based on their phylogenetic relationships. A comprehensive in-silico analysis was performed to determine chromosomal location, sub-cellular localization, and types of regulatory elements present in the putative promoter region. Synteny analysis revealed that GRF and GIF genes showed diploid-polyploid topology in pigeonpea, but not in chickpea. Tissue-specific expression data at the vegetative and reproductive stages of the plant showed that GRFs and GIFs were strongly expressed in tissues like embryos, pods, and seeds, indicating that GRFs and GIFs play vital roles in plant growth and development. This research characterized GRF and GIF families and hints at their primary roles in the chickpea and pigeonpea growth and developmental process. Our findings provide potential gene resources and vital information on GRF and GIF gene families in chickpea and pigeonpea, which will help further understand the regulatory role of these gene families in plant growth and development.

Exploration of the pearl millet phospholipase gene family to identify potential candidates for grain quality traits.

BACKGROUND: Phospholipases constitute a diverse category of enzymes responsible for the breakdown of phospholipids. Their involvement in signal transduction with a pivotal role in plant development and stress responses is well documented. RESULTS: In the present investigation, a thorough genome-wide analysis revealed that the pearl millet genome contains at least 44 phospholipase genes distributed across its 7 chromosomes, with chromosome one harbouring the highest number of these genes. The synteny analysis suggested a close genetic relationship of pearl millet phospholipases with that of foxtail millet and sorghum. All identified genes were examined to unravel their gene structures, protein attributes, cis-regulatory elements, and expression patterns in two pearl millet genotypes contrasting for rancidity. All the phospholipases have a high alpha-helix content and distorted regions within the predicted secondary structures. Moreover, many of these enzymes possess binding sites for both metal and non-metal ligands. Additionally, the putative promoter regions associated with these genes exhibit multiple copies of cis-elements specifically responsive to biotic and abiotic stress factors and signaling molecules. The transcriptional profiling of 44 phospholipase genes in two genotypes contrasting for rancidity across six key tissues during pearl millet growth revealed a predominant expression in grains, followed by seed coat and endosperm. Specifically, the genes PgPLD-alpha1-1, PgPLD-alpha1-5, PgPLD-delta1-7a, PgPLA1-II-1a, and PgPLD-delta1-2a exhibited notable expression in grains of both the genotypes while showing negligible expression in the other five tissues. The sequence alignment of putative promoters revealed several variations including SNPs and InDels. These variations resulted in modifications to the corresponding cis-acting elements, forming distinct transcription factor binding sites suggesting the transcriptional-level regulation for these five genes in pearl millet. CONCLUSIONS: The current study utilized a genome-wide computational analysis to characterize the phospholipase gene family in pearl millet. A comprehensive expression profile of 44 phospholipases led to the identification of five grain-specific candidates. This underscores a potential role for at least these five genes in grain quality traits including the regulation of rancidity in pearl millet. Therefore, this study marks the first exploration highlighting the possible impact of phospholipases towards enhancing agronomic traits in pearl millet.

CRISPR/Cas9-mediated mutagenesis of phytoene desaturase in pigeonpea and groundnut.

The CRISPR/Cas9 technology, renowned for its ability to induce precise genetic alterations in various crop species, has encountered challenges in its application to grain legume crops such as pigeonpea and groundnut. Despite attempts at gene editing in groundnut, the low rates of transformation and editing have impeded its widespread adoption in producing genetically modified plants. This study seeks to establish an effective CRISPR/Cas9 system in pigeonpea and groundnut through Agrobacterium-mediated transformation, with a focus on targeting the phytoene desaturase (PDS) gene. The PDS gene is pivotal in carotenoid biosynthesis, and its disruption leads to albino phenotypes and dwarfism. Two constructs (one each for pigeonpea and groundnut) were developed for the PDS gene, and transformation was carried out using different explants (leaf petiolar tissue for pigeonpea and cotyledonary nodes for groundnut). By adjusting the composition of the growth media and refining Agrobacterium infection techniques, transformation efficiencies of 15.2% in pigeonpea and 20% in groundnut were achieved. Mutation in PDS resulted in albino phenotype, with editing efficiencies ranging from 4 to 6%. Sequence analysis uncovered a nucleotide deletion (A) in pigeonpea and an A insertion in groundnut, leading to a premature stop codon and, thereby, an albino phenotype. This research offers a significant foundation for the swift assessment and enhancement of CRISPR/Cas9-based genome editing technologies in legume crops.

Genetic analysis of purple pigmentation in rice seed and vegetative parts - implications on developing high-yielding purple rice (Oryza sativa L.).

Pigmentation in rice grains is an important quality parameter. Purple-coloured rice (Oryza sativa L.) indicates the presence of high anthocyanin with benefits of antioxidant properties. However, the genetic mechanism of grain colour is not fully understood. Therefore, the study focused on understanding pigmentation in grain pericarp and vegetative parts, and its relationship with blast resistance and enhanced grain yield. Three local cultivars from the northeastern region (NER) of India - Chakhao Poireiton (purple), Mang Meikri (light brown), and Kala Joha (white) - along with high-yielding varieties (HYVs) Shasharang (light brown) and Sahbhagi dhan (white) were used to develop biparental populations. The findings suggested that pigmentation in vegetative tissue was governed by the inter-allelic interaction of several genes. Haplotype analysis revealed that Kala3 complemented Kala4 in enhancing purple pigmentation and that Kala4 is not the only gene responsible for purple colour as evident by the presence of a desired allele for markers RID3 and RID4 (Kala4 locus) in Chakhao Poireiton and Kala Joha irrespective of their pericarp colour, implying the involvement of some other additional, unidentified genes/loci. RID3 and RID4 together with RM15191 (Kala3 locus) could be employed as a reliable marker set for marker-assisted selection (MAS). Pericarp colour was strongly correlated with colour in different vegetative parts, but showed a negative correlation with grain yield. Pb1, reported to be associated with panicle blast resistance, contributed to leaf blast resistance. Transgressive segregants for improved pigmentation and high yield were identified. The selection of lines exhibiting coloured pericarp, high anthocyanin content, aroma, blast resistance, and increased yield compared to their respective HYV parents will be valuable resources in the rice breeding programme.

Pyramiding of qDTY1.1 and qDTY3.1 into rice mega-variety Samba Mahsuri-Sub1: physiological performance under water deficit conditions.

Water deficit is a crucial factor causing huge loss to rice productivity. The present study aimed to develop a multiple stress tolerant genotype by pyramiding drought tolerant yield QTLs qDTY1.1 and qDTY3.1 into high yielding rice variety Samba Mahsuri Sub-1(SMS) through marker assisted pyramiding. To achieve this six introgression lines of SMS carrying qDTY1.1 (SAB) were crossed with DRR-50, an Essentially Derived Variety of SMS carrying qDTY3.1. The SAB lines are taller than SMS due to tight linkage between qDTY1.1 and wild type SD-1. Therefore, F2 generation of crosses were screened for recombinants between SD-1 and qDTY1.1. Phenotyping of 1530 F2 plants representing three F2 populations from 35 F1 hybrids, identified 305 dwarf plants. Three dwarf F2 plants along with three others carrying qDTY1.1 and qDTY3.1 were forwarded to F3 generation. From the six F3 (SABD) lines fourteen pyramided progenies were selected and forward to F4 generation. The six SABD F3 lines SABD-7, SABD-8, SABD-9, SABD-76, SABD-79 and SABD-80 along with parents were evaluated under moisture stress (MS) for various physiological parameters. Chlorophyll and relative water content were more, while canopy temperature and malonaldehyde (MDA) content were lesser in SABD lines compared to parents indicating tolerance under MS. Variance due to genotypes was highly significant for all the yield related traits except test weight. Based on seed morphology, agronomic characters and physiological parameters six superior lines SABD-9-3, SABD-9-2, SABD-9-6, SABD-9-7, SABD-76-2 and SABD-76-6 performing better under MS were identified, which could be released after multi-location evaluation. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01387-5.

Playing with colours: genetics and regulatory mechanisms for anthocyanin pathway in cereals.

Cereals form the most important source of energy in our food. Currently, demand for coloured food grains is significantly increasing globally because of their antioxidant properties and enhanced nutritional value. Coloured grains of major and minor cereals are due to accumulation of secondary metabolites like carotenoids and flavonoids such as anthocyanin, proanthocyanin, phlobaphenes in pericarp, aleurone, lemma, testa or seed coat of grains. Differential accumulation of colour in grains is regulated by several regulatory proteins and enzymes involved in flavonoid and caroteniod biosynthesis. MYB and bHLH gene family members are the major regulators of these pathways. Genes for colour across various cereals have been extensively studied; however, only a few functional and allele-specific markers to be utilized directly in breeding programmes are reported so far. In this review, while briefly discussing the well studied and explored carotenoid pathway, we focus on a much more complex anthocyanin pathway that is found across cereals. The genes and their orthologs that are responsible for encoding key regulators of anthocyanin biosynthesis are discussed. This review also focuses on the genetic factors that influence colour change in different cereal crops, and the available/reported markers that can be used in breeding programs for utilizing this pathway for enhancing food and nutritional security.

A 1.84-Mb region on rice chromosome 2 carrying SPL4, SPL5 and MLO8 genes is associated with higher yield under phosphorus-deficient acidic soil.

Phosphorus (P) deficiency is one of the major limiting factors for rice productivity with only one locus (PSTOL1) available for field based application. A biparental mapping population (F6) derived from two P deficiency tolerant genotypes (Sahbhagi Dhan (SD) (PSTOL1+) and Chakhao Poreiton (CP) (PSTOL1-)), in which, transcriptome data generated from our lab had previously shown existence of diverse mechanisms was used to identify novel regions for better yield under lowland acidic soils. Phenotyping at F4, F5 and F6 generations revealed significant correlation between traits like tiller number at 30 days (TN 30), tiller number at 60 days (TN 60), filled grains (FG), percent spikelet fertility (SF%), panicle number (PN) and grain yield per panicle (GYPP) and also association with better yield/performance under low P acidic soil conditions. Through selected genotyping on a set of forty superior and inferior lines using SSR, candidate gene-based and SNP polymorphic markers, 5 genomic regions associated with various yield-related traits were identified. Marker trait association studies revealed 13 markers significantly associated with yield attributing traits and PUE under lowland acidic field conditions. Chi-square and regression analyses of markers run on the entire population identified seven and six markers for SF% and GYPP, respectively, and two for biological yield with positive allele derived from SD which constitute a novel 1.847-Mb region on chromosome 2 flanked by two markers RM12550 and PR9-2. Expression analysis of 7 candidate genes lying within this region across SD, CP and two low P susceptible rice genotypes has revealed that expression of four genes including SPL4, SPL5, ACA9 and MLO8 is significantly upregulated only in SD under low P conditions. In CP, there is low expression of MLO8 under low P conditions, whereas SPL4, SPL5 and Os02g08120 are downregulated. In the case of the two susceptible genotypes, there is no expression of Os02g08120 either in optimum or limiting conditions. Sequence data across a panel of 3024 rice genotypes also suggests that there is polymorphism for these differentially expressed genes. The genes and underlying markers identified on chromosome 2 will be key to imparting tolerance to low P in diverse genetic backgrounds and for marker-assisted selection for higher yield under lowland acidic conditions.

Root transcriptome reveals efficient cell signaling and energy conservation key to aluminum toxicity tolerance in acidic soil adapted rice genotype.

Aluminium (Al) toxicity is the single most important contributing factor constraining crop productivity in acidic soils. Hydroponics based screening of three rice genotypes, a tolerant (ARR09, AR), a susceptible (IR 1552, IR) and an acid soil adapted landrace (Theruvii, TH) revealed that AR accumulates less Al and shows minimum decrease in shoot and root biomass under Al toxicity conditions when compared with IR. Transcriptome data generated on roots (grown in presence or absence of Al) led to identification of ~1500 transcripts per genotype with percentage annotation ranging from 21.94% (AR) to 29.94% (TH). A total of 511, 804 and 912 DEGs were identified in genotypes AR, IR and TH, respectively. IR showed upregulation of transcripts involved in exergonic processes. AR appears to conserve energy by downregulating key genes of glycolysis pathway and maintaining transcript levels of key exergonic step enzymes under Al stress. The tolerance in AR appears to be as a result of novel mechanism as none of the reported Al toxicity genes or QTLs overlap with significant DEGs. Components of signal transduction and regulatory machinery like transcripts encoding zinc finger protein, calcieurin binding protein and cell wall associated transcripts are among the highly upregulated DEGs in AR, suggesting increased and better signal transduction in response to Al stress in tolerant rice. Sequencing of NRAT1 and glycine-rich protein A3 revealed distinct haplotype for indica type AR. The newly identified components of Al tolerance will help in designing molecular breeding tools to enhance rice productivity in acidic soils.

In silico characterization, and expression analysis of rice golden 2-like (OsGLK) members in response to low phosphorous.

The availability of phosphorus (P) affects productivity of rice. Under acidic soil conditions (pH < 5.5), P is rapidly immobilized in the soil. Several transcription factors play an important role in low Pi tolerance response, including MYB family members but their role in acidic soil is yet unknown. In this study, genome wide identification and characterization of golden 2-like (GLK) members belonging to GARP superfamily from rice (OsGLK) led to identification of 46 members distributed over 12 chromosomes. We assigned gene nomenclature, analyzed gene structure and identified mutant orthologs and phenotypes in maize and rice, respectively. On the basis of biological functions three categories viz., (a) two-component response regulator (five members), (b) putative transcription factor (21 members) and (c) phosphate starvation response (8 members) were identified. Phylogenetic analysis revealed a total of nine subgroups with MYB homeodomain-like and MYB CC-type domains conserved across members. Expression profiling of OsGLKs in response to 24 and 48 h of low Pi in four contrasting rice genotypes, revealed significantly higher expression of OsGLK10, OsGLK15, OsGLK22 and OsGLK30 in tolerant genotypes as compared to susceptible genotypes, suggesting their role in Pi starvation tolerance. Meta analyses and cis-regulatory elements (CREs) profiling of OsGLK showed diverse expression pattern in various tissues and organs and also modulation in response to various abiotic and biotic stresses. Our results highlight the versatile role of this diverse and complex GLK family, in particular to abiotic stress. These genes will form the basis of future studies on low Pi tolerance in acidic soils.

Marker-trait association for low-light intensity tolerance in rice genotypes from Eastern India.

Light intensity is a crucial environmental factor that affects photosynthesis and ultimately, grain yield in rice. However, no gene or marker directly associated with improved performance under low-light intensity under field conditions has been identified till date. With an aim of identifying genes and markers associated with improved performance (measured in terms of better yields) under low-light intensity, an integrated field screening, in silico and wet lab validation analysis was performed. Field-based screening of a diverse set of 110 genotypes led to the identification of two physiological and three morphological parameters critical for low-light tolerance in rice. In silico analysis using information available in public databases led to the identification of a set of 90 potential candidate genes which were narrowed to thirteen genic targets for possible marker-trait association. Marker-trait association on the panel of 48 diverse rice genotypes varying in their response to low-light intensity led to the identification of six markers [HvSSR02-44 (biological yield), HvSSR02-52 (spikelet fertility), HvSSR02-54 (grain yield), HvSSR06-56 (spikelet fertility), HvSSR06-69 (spikelet fertility; biological yield), HvSSR09-45 (spikelet fertility)] lying on chromosomes 2, 6 and 9 showing significant association (R2 > 0.1) for traits like grain yield/plant, biological yield and spikelet fertility under low light. Eight rice genes [including member of BBX (B-box) family] lying within 10 kb distance of these identified markers already reported for their role in response to stress or change in plant architecture in rice were also identified. The eight rice genotypes, five traits, eight genes and six markers identified in the current study will help in devising strategies to increase yield under low light intensity and pave way for future application in marker-assisted breeding.

In silico characterisation of novel rice transcripts differentially expressed in phosphorus dificient conditions suggests a role of these transcripts in multiple abiotic stresses.

Phosphorus deficiency adversely affects crop productivity. The mechanism of tolerance in plants is not well understood. The current study successfully annotated a set of highly significant (Log2 RPKM ≥3) nine novel sequences up-regulated in P deficient condition identified from a low P tolerant rice genotype. Sequence annotation identified two transcripts (Os01g37260 and Os02g11060) carrying known domains, F-box and WD, respectively. Multiple Expectation maximization for Motif Elicitation (MEME) revealed presence of conserved domains like D[LP][HY][CL]D[CM][DT]C[AP][DQ][IQ]C, [EH][DN]HN[HS] [ER][FY][EP]I[HN]H which might play a role in phosphorus deficiency tolerance. Analysis of the upstream regions indicated presence of stress responsive elements like E Box, ABRE, and MYBCORE suggesting regulation of the novel transcripts by DNA binding. Protein localization prediction tool suggests that these novel proteins might be targeted to nucleus, chloroplast and cell wall. Transcripts Os02g03640 and Os02g10250 revealed potential target sites for microRNA binding suggesting role of novel miRNAs in low phosphorus response. Our analysis suggests that an F-box protein, Os01g37260 (OSFBx14) might be a promising candidate gene playing a role in multiple abiotic stresses including P deficiency.

Understanding Fe2+ toxicity and P deficiency tolerance in rice for enhancing productivity under acidic soils.

Plants experience low phosphorus (P) and high iron (Fe) levels in acidic lowland soils that lead to reduced crop productivity. A better understanding of the relationship between these two stresses at molecular and physiological level will lead to development of suitable strategies to increase crop productivity in such poor soils. Tolerance for most abiotic stresses including P deficiency and Fe toxicity is a quantitative trait in rice. Recent studies in the areas of physiology, genetics, and overall metabolic pathways in response to P deficiency of rice plants have improved our understanding of low P tolerance. Phosphorous uptake and P use efficiency are the two key traits for improving P deficiency tolerance. In the case of Fe toxicity tolerance, QTLs have been reported but the identity and role played by underlying genes is just emerging. Details pertaining to Fe deficiency tolerance in rice are well worked out including genes involved in Fe sensing and uptake. But, how rice copes with Fe toxicity is not clearly understood. This review focuses on the progress made in understanding these key environmental stresses. Finally, an opinion on the key genes which can be targeted for this stress is provided.

Functional properties of an alternative, tissue-specific promoter for rice NADPH-dependent dihydroflavonol reductase.

NADPH-dependent dihydroflavonol reductase (DFR) plays an important role in both anthocyanin biosynthesis and proanthocyanidin synthesis in plants. A specific and quantitative RT-PCR assay for transcription from the DFR promoter detected high expression with limited variability in rice tissues. A 440 bp minimal promoter region was identified by transfection of ß-glucuronidase (GUS) reporter constructs into Jeokjinju variety. Alignment of the region with orthologous promoters revealed three conserved segments containing both bHLH (-386 to -381) and Myb (-368 to -362) binding sites. Transfection of ß-glucuronidase constructs with targeted point mutations in the minimal promoter defined two sites important for promoter function to the transcription factor binding consensus sequences. The expression study showed that the bHLH binding domain (-386 to -381) is essential for DFR expression, and that a Myb binding domain (-368 to -362) is also required for full expression of the DFR gene, while the two bHLH binding domains (-104 to -99 and -27 to -22) nearest to the transcriptional start site are not necessary for DFR expression.

Root transcriptomes of two acidic soil adapted Indica rice genotypes suggest diverse and complex mechanism of low phosphorus tolerance.

Low phosphorus (P) tolerance in rice is a biologically and agronomically important character. Low P tolerant Indica-type rice genotypes, Sahbhagi Dhan (SD) and Chakhao Poreiton (CP), are adapted to acidic soils and show variable response to low P levels. Using RNAseq approach, transcriptome data was generated from roots of SD and CP after 15 days of low P treatment to understand differences and similarities at molecular level. In response to low P, number of genes up-regulated (1318) was more when compared with down-regulated genes (761). Eight hundred twenty-one genes found to be significantly regulated between SD and CP in response to low P. De novo assembly using plant database led to further identification of 1535 novel transcripts. Functional annotation of significantly expressed genes suggests two distinct methods of low P tolerance. While root system architecture in SD works through serine-threonine kinase PSTOL1, suberin-mediated cell wall modification seems to be key in CP. The transcription data indicated that CP relies more on releasing its internally bound Pi and coping with low P levels by transcriptional and translational modifications and using dehydration response-based signals. Role of P transporters seems to be vital in response to low P in CP while sugar- and auxin-mediated pathway seems to be preferred in SD. At least six small RNA clusters overlap with transcripts highly expressed under low P, suggesting role of RNA super clusters in nutrient response in plants. These results help us to understand and thereby devise better strategy to enhance low P tolerance in Indica-type rice.

Population Dynamics Among six Major Groups of the Oryza rufipogon Species Complex, Wild Relative of Cultivated Asian Rice.

BACKGROUND: Understanding population structure of the wild progenitor of Asian cultivated rice (O. sativa), the Oryza rufipogon species complex (ORSC), is of interest to plant breeders and contributes to our understanding of rice domestication. A collection of 286 diverse ORSC accessions was evaluated for nuclear variation using genotyping-by-sequencing (113,739 SNPs) and for chloroplast variation using Sanger sequencing (25 polymorphic sites). RESULTS: Six wild subpopulations were identified, with 25 % of accessions classified as admixed. Three of the wild groups were genetically and geographically closely related to the O. sativa subpopulations, indica, aus and japonica, and carried O. sativa introgressions; the other three wild groups were genetically divergent, had unique chloroplast haplotypes, and were located at the geographical extremes of the species range. The genetic subpopulations were significantly correlated (r 2 = 0.562) with traditional species designations, O. rufipogon (perennial) and O. nivara (annual), differentiated based on morphology and life history. A wild diversity panel of 95 purified (inbred) accessions was developed for future genetic studies. CONCLUSIONS: Our results suggest that the cultivated aus subpopulation is most closely related to an annual wild relative, japonica to a perennial wild relative, and indica to an admixed population of diverse annual and perennial wild ancestors. Gene flow between ORSC and O. sativa is common in regions where rice is cultivated, threatening the identity and diversity of wild ORSC populations. The three geographically isolated ORSC populations harbor variation rarely seen in cultivated rice and provide a unique window into the genetic composition of ancient rice subpopulations.

Seedling stage low temperature response in tolerant and susceptible rice genotypes suggests role of relative water content and members of OsSNAC gene family.

Low temperature (LT) severely affects rice growth and grain yield. Recently, we reported contrasting genotypes including ARR 09 and Takyer for seedling stage long duration low temperature response. Here we show that susceptible rice genotypes show an increase in lipid peroxide levels and decrease in relative water content (RWC) to a higher extent in comparison to tolerant genotypes in response to 3 h LT. Stress induced NAC family members (OsNAC1, OsNAC2, OsNAC3, and OsNAC5) showed a higher transcript accumulation in tolerant genotypes than in sensitive genotypes after LT treatment suggesting stress tolerance might be due to higher expression of stress-responsive transcription factors. Furthermore, ARR 09 can be used as an important genetic resource to better understand LT tolerance mechanism.

Allele mining across DREB1A and DREB1B in diverse rice genotypes suggest a highly conserved pathway inducible by low temperature.

Low temperature stress is one of the major limiting factors affecting rice productivity in higher altitudes. DREB1A and DREB1B, are two transcription factors that have been reported to play key regulatory role in low temperature tolerance. In order to understand whether natural genetic variation in these two loci leads to cold tolerance or susceptibility, OsDREB1A and OsDREB1B were targeted across several rice genotypes showing differential response to low temperature. Expression data suggests induction of gene expression in shoots in response to low temperature in both tolerant and susceptible genotypes. Upon sequence analysis of 20 rice genotypes, eight nucleotide changes were identified including two in the coding region and six in the 5'UTR. None of the discovered novel variations lie in the conserved region of the genes under study, thereby causing little or no changes in putative function of the corresponding proteins. In silico analysis using a diverse set of 400 O. sativa revealed much lower nucleotide diversity estimates across two DREB loci and one other gene (MYB2) involved in DREB pathway than those observed for other rice genes. None of the changes showed association with seedling stage cold tolerance, suggesting that nucleotide changes in DREB loci are unlikely to contribute to low temperature tolerance. So far, data concerning the physiological role and regulation of DREB1 in different genetic background are very limited; it is to be expected that they will be studied extensively in the near future.