Modulating ABA-dependent growth and development by overexpressing cytochrome P450 ABA 8′-hydroxylase in Medicago truncatula

Abstract

Abscisic acid (ABA) is a pivotal phytohormone involved in regulating various aspects of plant growth, development, and responses to environmental stress. The Cytochrome P450 family member ABA 8′-hydroxylase (8′OH-ABA) is proposed to play a central role in the catabolic degradation of ABA. In the present study, the 8'OH-ABA gene from Medicago truncatula was isolated and functionally characterized using transgenic overexpression approaches. Under non-stress conditions, plants overexpressing 8'-OH-ABA displayed notable phenotypic variations compared to wild-type plants, including altered leaf morphology, an extended lifespan, and delayed flowering. Scanning electron microscopy (SEM) analysis revealed a reduction in cell spacing and curvature at the leaf margins, which was attributed to the smaller size of epidermal cells in the stem, ultimately contributing to a slower growth rate. Furthermore, these overexpressing plants exhibited heightened sensitivity to drought stress, an effect closely associated with 8′OH-ABA expression. Transcriptome analysis revealed 3814 differentially expressed genes (DEGs), with 13 genes enriched in the "abscisic acid-activated signaling pathway" and 29 in the "carotenoid biosynthesis" pathway. Notably, we identified genes directly linked to ABA responses, including the ABA 8′-hydroxylase CYP707A2, the transcription factor gene MYC2, and the cytochrome P450 enzyme CYP78A5, which regulates organ size and leaf development. Collectively, these findings indicated the regulatory role of 8’OH-ABA in plant development and drought stress response, thereby highlighting the importance of ABA signaling in these biological processes.