Characterization of rhizospheric fungi and their in vitro antagonistic potential against myco-phytopathogens invading Macrotyloma uniflorum plants.

Microorganisms have become more resistant to pesticides, which increases their ability to invade and infect crops resulting in decreased crop productivity. The rhizosphere plays a crucial role in protecting plants from harmful invaders. The purpose of the study was to investigate the antagonistic efficiency of indigenous rhizospheric fungal isolates against phytopathogens of M. uniflorum plants so that they could be further used as potent Biocontrol agents. Thirty rhizospheric fungal isolates were collected from the roots of the Macrotyloma uniflorum plant and initially described morphologically for the present study. Further, in vitro tests were conducted to evaluate the antifungal activity of these strains against four myco-phytopathogens namely Macrophamina phaseolina, Phomopsis sp. PhSFX-1, Nigrospora oryzae, and Boeremia exigua. These pathogens are known to infect the same crop plant, M. uniflorum, and cause declines in crop productivity. Fifteen fungal strains out of the thirty fungal isolates showed some partial antagonistic activity against the myco-phytopathogens. The potent fungal isolates were further identified using molecular techniques, specifically based on the internal transcribed spacer (ITS) region sequencing. Penicillium mallochii, Cladosporium pseudocladosporioides, Aspergillus chevalieri, Epicoccum nigrum, Metarhizium anisopliae, and Mucor irregularis were among the strains that were identified. These potent fungal strains showed effective antagonistic activity against harmful phytopathogens. Current findings suggest that these strains may be taken into consideration as synthetic fungicides which are frequently employed to manage plant diseases alternatives.

Elucidating the unknown transcriptional responses and PHR1-mediated biotic and abiotic stress tolerance during phosphorus limitation.

Phosphorus (P) limitation in the majority of world soils is a major constraint for plant growth and crop productivity. RNA sequencing was used to discover novel P-responsive gene transcripts (PRGTs) in leaves and roots of Arabidopsis. Hisat StringTie and the Cufflinks TopHat transcript assembler were used to analyze reads and identify 1074 PRGTs with a >5-fold altered abundance during P limitation. Interestingly, 60% of these transcripts were not previously reported. Among the novel PRGTs, 106 were from unannotated genes, and some were among the most P-responsive, including At2g36727 which encodes a novel miRNA. Annotated novel PRGTs encode transcription factors, miRNAs, small signaling peptides, long non-coding RNAs, defense-related proteins, and transporters, along with proteins involved in many biological processes. We identified several genes that undergo alternative splicing during P limitation, including a novel miR399-resistant splice variant of PHOSPHATE2 (PHO2.2). Several novel P-responsive genes were regulated by PHOSPHATE STARVATION RESPONSE1 (PHR1), PHR1-LIKE 1 (PHL1), and PHO2. We discovered that P-limited plants show increased resistance to pathogens and drought stress mediated by PHR1-PHL1. Identification of novel P-responsive transcripts and the discovery of the influence of P limitation on biotic and abiotic stress adds a significant component to our understanding of plant P signaling.

Overexpression of Arabidopsis nucleolar GTP-binding 1 (NOG1) proteins confers drought tolerance in rice.

As a major adverse environmental factor in most parts of the world, drought causes substantial crop yield losses. Rice (Oryza sativa) is one of the staple foods for more than one-half of the world's population. Rice plants are sensitive to even mild drought stress and need almost twice the amount of water compared to wheat (Triticum aestivum) or maize (Zea mays). Arabidopsis (Arabidopsis thaliana) small GTPase Nucleolar GTP-binding protein 1 (AtNOG1) plays a role in biotic stress tolerance. Here, we created transgenic rice lines constitutively overexpressing AtNOG1-1 or AtNOG1-2. We also developed rice RNA interference (RNAi) lines that show downregulation of OsNOG1. AtNOG1-1 and AtNOG1-2 overexpressors showed enhanced drought tolerance without compromising grain yield, whereas OsNOG1-RNAi was more susceptible to drought when compared to wild-type plants. Analysis of physiological parameters showed increased cell sap osmolality, relative water content, and abscisic acid (ABA) level, but decreased leaf water loss in AtNOG1-1 or AtNOG1-2 overexpressor lines compared to the control. We found upregulation of several genes involved in ABA and jasmonic acid (JA) signaling, stomata regulation, osmotic potential maintenance, stress protection, and disease resistance in AtNOG1-1 and AtNOG1-2 overexpressor lines compared to the control. We elucidated the role of NOG1-2 and NOG1-1 in regulation of silica body formation around stomata to prevent transpirational water loss. These results provide an avenue to confer drought tolerance in rice.

Genome-Wide Identification of Medicago Peptides Involved in Macronutrient Responses and Nodulation.

Growing evidence indicates that small, secreted peptides (SSPs) play critical roles in legume growth and development, yet the annotation of SSP-coding genes is far from complete. Systematic reannotation of the Medicago truncatula genome identified 1,970 homologs of established SSP gene families and an additional 2,455 genes that are potentially novel SSPs, previously unreported in the literature. The expression patterns of known and putative SSP genes based on 144 RNA sequencing data sets covering various stages of macronutrient deficiencies and symbiotic interactions with rhizobia and mycorrhiza were investigated. Focusing on those known or suspected to act via receptor-mediated signaling, 240 nutrient-responsive and 365 nodulation-responsive Signaling-SSPs were identified, greatly expanding the number of SSP gene families potentially involved in acclimation to nutrient deficiencies and nodulation. Synthetic peptide applications were shown to alter root growth and nodulation phenotypes, revealing additional regulators of legume nutrient acquisition. Our results constitute a powerful resource enabling further investigations of specific SSP functions via peptide treatment and reverse genetics.

The transcription factor PHR1 regulates lipid remodeling and triacylglycerol accumulation in Arabidopsis thaliana during phosphorus starvation.

Lipid remodeling is one of the most dramatic metabolic responses to phosphorus (P) starvation. It consists of the degradation of phospholipids to release the phosphate needed by the cell and the accumulation of glycolipids to replace phospholipids in the membranes. It is shown that PHR1, a well-described transcriptional regulator of P starvation of the MYB family, largely controls this response. Glycerolipid composition and the expression of most lipid-remodeling gene transcripts analysed were altered in the phr1 mutant under phosphate starvation in comparison to wild-type plants. In addition to these results, the lipidomic characterization of wild-type plants showed two novel features of the lipid response to P starvation for Arabidopsis. Triacylglycerol (TAG) accumulates dramatically under P starvation (by as much as ~20-fold in shoots and ~13-fold in roots), a response known to occur in green algae but hardly known in plants. Surprisingly, there was an increase in phosphatidylglycerol (PG) in P-starved roots, a response that may be adaptive as it was suppressed in the phr1 mutant.

Identification of primary and secondary metabolites with phosphorus status-dependent abundance in Arabidopsis, and of the transcription factor PHR1 as a major regulator of metabolic changes during phosphorus limitation.

Massive changes in gene expression occur when plants are subjected to phosphorus (P) limitation, but the breadth of metabolic changes in these conditions and their regulation is barely investigated. Nearly 350 primary and secondary metabolites were profiled in shoots and roots of P-replete and P-deprived Arabidopsis thaliana wild type and mutants of the central P-signalling components PHR1 and PHO2, and microRNA399 overexpresser. In the wild type, the levels of 87 primary metabolites, including phosphorylated metabolites but not 3-phosphoglycerate, decreased, whereas the concentrations of most organic acids, amino acids, nitrogenous compounds, polyhydroxy acids and sugars increased. Furthermore, the levels of 35 secondary metabolites, including glucosinolates, benzoides, phenylpropanoids and flavonoids, were altered during P limitation. Observed changes indicated P-saving strategies, increased photorespiration and crosstalk between P limitation and sulphur and nitrogen metabolism. The phr1 mutation had a remarkably pronounced effect on the metabolic P-limitation response, providing evidence that PHR1 is a key factor for metabolic reprogramming during P limitation. The effects of pho2 or microRNA399 overexpression were comparatively minor. In addition, positive correlations between metabolites and gene transcripts encoding pathway enzymes were revealed. This study provides an unprecedented metabolic phenotype during P limitation in Arabidopsis.