A SHORTROOT-Mediated Transcriptional Regulatory Network for Vascular Development in the Arabidopsis Shoot

In plants, vascular development is a dynamic process that integrates extrinsic and intrinsic factors. In Arabidopsis (Arabidopsis thaliana), SHORTROOT (SHR) has been known to play key roles in regulating cell division and differentiation in root vascular development. However, the role of SHR in the shoot vasculature remains unknown. Here, we employed various experimental approaches to unravel SHR's role in shoot vascular development. In hypocotyls and inflorescence stems, shr exhibited reduced cell numbers in the (pro)cambium. As a result, the daughter cells that would be incorporated into the phloem and xylem would become a shortage of supply, thereby causing precocious differentiation. By expression profiling, we identified a putative SHR-mediated transcriptional regulatory network (TRN), which includes a subset of the ETHYLENE RESPONSE FACTOR (ERF) family. Among these, we found that SHR directly regulated expression of ERF018, whose expression domains were largely overlapped with those of SHR. Additionally, we found that ERF018 overexpressors (ERF018-OXs) showed a reduction in cambium cell division in hypocotyls. Interestingly, the level of SHR transcripts was elevated in ERF018-OX hypocotyls. Taken together, our results provide insights into the previously uncharacterized role of SHR, implying that maintaining homeostasis of key regulators' levels plays an important role in shoot vascular development.