| Plant morphology is based on the coordination of growth and development with endogenous and exogenous cues. Significant progress has been made in identification of endogenous cues regulating plant development and characterizing plant response to environmental cues. However, how these two processes are integrated into establishment of a plant's final form remains largely unknown. To gain insight into the molecular mechanisms regulating leaf development, a genetic screen was carried out in Arabidopsis. We identified mutants with defects in the BYPASS1 (BPS1) gene in this screen. To characterize the function of BPS1 in leaf development, a combination of physiological, genetic, biochemical, and molecular approaches was employed.; Mutation of the BPS1 gene results in seedlings with defects in both leaf and root development. We linked bps1 leaf development defects to a signal emanating from the bps1 root, and showed that the signal is sufficient to arrest development in wild type leaves. BPS1 encodes a plant-specific protein of unknown function; however, we propose that BPS1 functions to negatively regulate production of the root-derived signal. We determined that postembryonic root development is required for signal production. We also showed the BPS1-regulated signal is not one of the previously characterized plant hormones, but its production requires the carotenoid biosynthetic pathway, and it appears to be a novel compound derived from zeaxanthin. Root-to-shoot transport of the BPS1-regulated signal does not require functional xylem or phloem.; Examination of two BPS1 related genes in Arabidopsis, BYPASS2 (BPS2) and BYPASS3 ( BPS3) revealed that neither of these genes has a unique role in plant development. However, plants carrying mutations in both BPS1 and BPS2 showed defects in embryo development. These results indicate that BPS1 and BPS2 may have partially redundant functions and suggest that repression of the BPS1-regulated signal may be important for normal embryogenesis.; How the root-derived signal affects shoot development is not currently known. However, based on data from bps1 and bps1 bps2 mutants, the target of the BPS1-regulated signal may be auxin perception or response. Together, our data indicate that BPS1 regulates a novel root-to-shoot signaling pathway and the BPS1-regulated signal is a novel plant hormone. |
