ABA-induced MYB transcriptional module regulates the differentiation trajectory of chickpea exodermis

Abscisic acid (ABA) regulates plant responses to stress and influences the differentiation of root barrier cell types, such as the endodermis and exodermis. Despite the importance of the exodermis in limiting water and solute fluxes, its regulation remains poorly understood in legumes. Here, we characterize the ABA-induced suberization and lignification of root tissues across eight galegoid legumes to identify exodermis-forming species in the clade. Chickpea deposited suberin lamella specifically in the outermost cortex and formed a functional apoplastic barrier, i.e. an exodermis. Transcriptomics of chickpea roots revealed ABA-induced programs that were temporally separated, specifically, a rapid program with the general ABA response, and a delayed programs of suberin and lignin biosynthesis. We identified WRKY and MYB transcription factors that putatively link the ABA response to the suberin biosynthesis, and using single-cell RNA-seq of chickpea roots we inferred an exodermis-expressed WRKY-MYB regulatory unit upstream of the suberin biosynthetic genes. Transactivation assays supported an ABA-dependent transcription factor activity upstream of suberin biosynthesis pathway in chickpea. Our results reveal a cell-type specific transcription factor hierarchy that coordinates hormone perception into an important mechanism of root plasticity in legumes.