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The use of beneficial microbes to mitigate drought stress tolerance of plants is of great potential albeit little understood. We show here that a root endophytic desert bacterium, Pseudomonas argentinensis strain SA190, enhances drought stress tolerance in Arabidopsis. Transcriptome and genetic analysis demonstrate that SA190-induced root morphogenesis and gene expression is mediated via the plant abscisic acid (ABA) pathway. Moreover, we demonstrate that SA190 primes the promoters of target genes in an epigenetic ABA-dependent manner. Application of SA190 priming on crops is demonstrated for alfalfa, showing enhanced performance under drought conditions. In summary, a single beneficial root bacterial strain can help plants to resist drought conditions.

Post-transcriptional regulation of mRNA mediated by methylation at the N⁶ position of adenine (N⁶-methyladenosine (m⁶A)) has profound effects on transcriptome regulation in plants. Focused studies across eukaryotes offer glimpses into the processes governed by m⁶A throughout developmental and disease states. However, we lack an understanding of the dynamics and the regulatory potential of m⁶A during biotic stress in plants. Here, we provide a comprehensive look into the effects of m⁶A on both the short-term and long-term response to pathogen signaling in Arabidopsis (Arabidopsis thaliana). We demonstrate that m⁶A-deficient plants are more resistant to bacterial and fungal pathogen infections and have altered immune responses. Furthermore, m⁶A deposition is specifically coordinated on transcripts involved in defense and immunity prior to and proceeding the pathogen signal flagellin. Consequently, the dynamic modulation of m⁶A on specific stress-responsive transcripts is correlated with changes in abundance and cleavage of these transcripts. Overall, we show that the m⁶A methylome is regulated prior to and during simulated and active pathogen stress and functions in the coordination and balancing of normal growth and pathogen responses.

Senescence is an important physiological process which directly affects many agronomic traits in plants. Senescence induces chlorophyll degradation, phytohormone changes, cellular structure damage, and altered gene regulation. Although these physiological outputs are well defined, the molecular mechanisms employed are not known. Using dark-induced leaf senescence (DILS) as the experimental system, we investigated the role of N⁶-methyladenosine (m⁶A) mRNA methylation during senescence in Arabidopsis (Arabidopsis thaliana). Plants compromised in m⁶A machinery components like METHYLTRANSFERASE A (mta mutant) and VIRILIZER1 (vir-1 mutant) showed an enhanced DILS phenotype. This was accompanied by compromised chloroplast and photosynthesis performance in mta as well as accumulation of senescence-promoting camalexin and phytohormone jasmonic acid after dark treatment. m⁶A levels increased during DILS and destabilized senescence-related transcripts thereby preventing premature aging. Due to inefficient decay, senescence-related transcripts like ORESARA1 (ORE1), SENESCENCE-ASSOCIATED GENE 21 (SAG21), NAC-like, activated by AP3/PI (NAP), and NONYELLOWING 1 (NYE1) over-accumulated in mta thereby causing accelerated senescence during DILS. Overall, our data propose that m⁶A modification is involved in regulating the biological response to senescence in plants, providing targets for engineering stress tolerance of crops.

Linker H1 histones play an important role in animal and human pathogenesis, but their function in plant immunity is poorly understood. Here, we analyzed mutants of the three canonical variants of Arabidopsis H1 histones, namely H1.1, H1.2 and H1.3. We observed that double h1.1h1.2 and triple h1.1h1.2h1.3 (3h1) mutants were resistant to Pseudomonas syringae and Botrytis cinerea infections. Transcriptome analysis of 3h1 mutant plants showed H1s play a key role in regulating the expression of early and late defense genes upon pathogen challenge. Moreover, 3h1 mutant plants showed enhanced production of reactive oxygen species and activation of mitogen activated protein kinases upon pathogen-associated molecular pattern (PAMP) treatment. However, 3h1 mutant plants were insensitive to priming with flg22, a well-known bacterial PAMP which induces enhanced resistance in WT plants. The defective defense response in 3h1 upon priming was correlated with altered DNA methylation and reduced global H3K56ac levels. Our data place H1 as a molecular gatekeeper in governing dynamic changes in the chromatin landscape of defense genes during plant pathogen interaction.