Department of Biological Sciences
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Item Constitutively photomorphogenic1 promotes ABA-mediated inhibition of post-germination seedling establishment(Wiley, 2020-05) Yadukrishnan, PremachandranUnder acute stress conditions, precocious seedling development may result in the premature death of young seedlings, before they switch to autotrophic growth. The phytohormone abscisic acid (ABA) inhibits seed germination and post-germination seedling establishment under unfavorable conditions. Various environmental signals interact with the ABA pathway to optimize these early developmental events under stress. Here, we show that light availability critically influences ABA sensitivity during early seedling development. In dark conditions, the ABA-mediated inhibition of post-germination seedling establishment is strongly enhanced. COP1, a central regulator of seedling development in the dark, is necessary for this enhanced post-germination ABA sensitivity in darkness. Despite their slower germination, cop1 seedlings establish faster than wild type in the presence of ABA in both light and dark. PHY and CRY photoreceptors that inhibit COP1 activity in light modulate ABA-mediated inhibition of seedling establishment in light. Genetically, COP1 acts downstream to ABI5, a key transcriptional regulator of ABA signaling, and does not influence the transcriptional and protein levels of ABI5 during the early post-germination stages. COP1 promotes post-germination growth arrest independent of the antagonistic interaction between ABA and cytokinin signaling pathways. COP1 facilitates the binding of ABI5 on its target promoters and the ABA-mediated upregulation of these target genes is reduced in cop1-4. Together, our results suggest that COP1 positively regulates ABA signaling to inhibit post-germination seedling establishment under stress.Item Triggered in distress: a miRNA-controlled switch for drought-induced ABA biosynthesis in rice(OUP, 2022-06) Yadukrishnan, PremachandranAbiotic stress conditions such as drought, salinity, and flood challenge agricultural production worldwide by adversely affecting crop growth and yield. Plants inherently possess sophisticated response mechanisms for adjusting their physiology to improve survival under stress conditions. Understanding these mechanisms and enhancing them through breeding and biotechnological means are important steps toward developing crop varieties that can perform well under unpredictable climatic extremities of the future. Abscisic acid (ABA) is a key phytohormone that mediates stress responses in all land plants. Stress conditions induce ABA biosynthesis through a series of steps that occur in plastids and cytosol, and the rate-limiting step in this process is catalyzed by enzymes known as 9-cis-epoxycarotenoid dioxygenases (NCEDs) (Nambara and Marion-Poll, 2005). ABA activates a signaling cascade featuring a set of receptors that function redundantly, type 2C protein phosphatases (PP2Cs) that act as co-receptors, sucrose non-fermenting 1-related protein kinase 2 subfamily proteins (SnRK2s) that channel the signal from cytosol to nucleus, and an array of transcription factors that mediate stress-responsive gene expression (Chen et al., 2020). Since elevated levels of ABA can often impart negative effects on growth, a tight modulation of ABA biosynthesis and signaling is necessary to balance growth and stress responses (Chen et al., 2020). In addition to transcriptional regulation, the levels and activities of ABA signaling components are optimized at the post-transcriptional level by miRNAs and at the protein level through post-translational modifications (Nadarajah and Kumar, 2019; Zhang et al., 2019; Chen et al., 2020). However, the precise mechanisms by which ABA biosynthesis is rapidly induced under stress conditions and turned off immediately when the normal growth conditions are restored remain poorly understood.Item A COP1-HY5-ABI5 module regulates ABA-mediated post-germination developmental arrest(Frontiers Media, 2025-11) Yadukrishnan, PremachandranAbscisic Acid (ABA) is a key phytohormone that regulates plant development under stress. ABA induces dormancy in seeds during maturation, whereas its levels and activity gradually decrease as germination and seedling growth progress. Under abiotic stress conditions, elevated levels of ABA inhibit seed germination and/or impose post-germination growth arrest. The transcription factor ABSCISIC ACID INSENSITIVE 5 (ABI5) regulates the interplay between ABA and light signaling to modulate this process. The light-regulated transcription factor ELONGATED HYPOCOTYL 5 (HY5) modulates ABA-mediated inhibition of post-germination development. However, the interrelation between HY5 and ABI5 in regulating post-germination development remains poorly understood. Here, using molecular, genetic, and biochemical approaches, we show that ABI5 and HY5 proteins reciprocally influence each other’s accumulation during early plant development. We further find that ABA induces nuclear accumulation of COP1, which correlates with reduced HY5 levels and enhanced ABI5 accumulation under stress conditions. Together, our results support a model in which a double-negative feedback loop between HY5 and ABI5 contributes to ABA-mediated post-germination growth arrest.