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The plant hormone abscisic acid (ABA) triggers cellular tolerance responses to osmotic stress caused by drought and salinity. ABA controls the turgor pressure of guard cells in the plant epidermis, leading to stomatal closure to minimize water loss. However, stomatal apertures open to uptake CO 2 for photosynthesis even under stress conditions. ABA modulates its signaling pathway via negative feedback regulation to maintain plant homeostasis. In the nuclei of guard cells, the clade A type 2C protein phosphatases (PP2Cs) counteract SnRK2 kinases by physical interaction, and thereby inhibit activation of the transcription factors that mediate ABA-responsive gene expression. Under osmotic stress conditions, PP2Cs bind to soluble ABA receptors to capture ABA and release active SnRK2s. Thus, PP2Cs function as a switch at the center of the ABA signaling network. ABA induces the expression of genes encoding repressors or activators of PP2C gene transcription. These regulators mediate the conversion of PP2C chromatins from a repressive to an active state for gene transcription. The stress-induced chromatin remodeling states of ABA-responsive genes could be memorized and transmitted to plant progeny; i.e., transgenerational epigenetic inheritance. This review focuses on the mechanism by which PP2C gene transcription modulates ABA signaling.

The Arabidopsis thaliana transcription factor gene AtMYB44 was induced within 10 min by treatment with methyl jasmonate (MeJA). Wound-induced expression of the gene was observed in local leaves, but not in distal leaves, illustrating jasmonate-independent induction at wound sites. AtMYB44 expression was not abolished in Arabidopsis mutants insensitive to jasmonate (coi1), ethylene (etr1), or abscisic acid (abi3-1) when treated with the corresponding hormones. Moreover, various growth hormones and sugars also induced rapid AtMYB44 transcript accumulation. Thus, AtMYB44 gene activation appears to not be induced by any specific hormone. MeJA-induced activation of jasmonate-responsive genes such as JR2, VSP, LOXII, and AOS was attenuated in transgenic Arabidopsis plants overexpressing the gene (35S:AtMYB44), but significantly enhanced in atmyb44 knockout mutants. The 35S:MYB44 and atmyb44 plants did not show defectiveness in MeJA-induced primary root growth inhibition, indicating that the differences in jasmonate-responsive gene expression observed was not due to alterations in the jasmonate signaling pathway. 35S:AtMYB44 seedlings exhibited slightly elevated chlorophyll levels and less jasmonate- induced anthocyanin accumulation, demonstrating suppression of jasmonate-mediated responses and enhancement of ABA-mediated responses. These observations support the hypothesis of mutual antagonistic actions between jasmonate- and abscisic acid-mediated signaling pathways.

Summary: Alternative splicing (AS) is a critical means by which plants respond to changes in the environment, but few splicing factors contributing to AS have been reported and functionally characterized in rice (Oryza sativa L.). Here, we explored the function and molecular mechanism of the spliceosome‐associated protein OsFKBP20‐1b during AS.We determined the AS landscape of wild‐type and osfkbp20‐1b knockout plants upon abscisic acid (ABA) treatment by transcriptome deep sequencing. To capture the dynamics of translating intron‐containing mRNAs, we blocked transcription with cordycepin and performed polysome profiling. We also analyzed whether OsFKBP20‐1b and the splicing factors OsSR34 and OsSR45 function together in AS using protoplast transfection assays.We show that OsFKBP20‐1b interacts with OsSR34 and regulates its stability, suggesting a role as a chaperone‐like protein in the spliceosome. OsFKBP20‐1b facilitates the splicing of mRNAs with retained introns after ABA treatment; some of these mRNAs are translatable and encode functional transcriptional regulators of stress‐responsive genes. In addition, interacting proteins, OsSR34 and OsSR45, regulate the splicing of the same retained introns as OsFKBP20‐1b after ABA treatment.Our findings reveal that spliceosome‐associated immunophilin functions in alternative RNA splicing in rice by positively regulating the splicing of retained introns to limit ABA response. [ABSTRACT FROM AUTHOR]