Beyond the phloem: A general role of the Arabidopsis OCTOPUS gene family in controlling plant growth vigour

OCTOPUS (OPS) and OCTOPUS-LIKE 2 (OPL2), two homologous genes, were previously identified as important regulators of phloem differentiation in Arabidopsis roots, impacting root growth when their function is lost. Here, we investigated the roles of the other three OPS homologs in Arabidopsis, OPL1, OPL3, and OPL4. We employed promoter activity analyses, protein localisation studies, functional complementation assays, analysis of single and multiple mutant combinations, and growth assays, including exposure to CLE45 and brassinosteroid pathway modulators. The OPS/OPL genes exhibit overlapping expression patterns and functions. Multiple mutant combinations revealed a high degree of redundancy, with OPS and the phloem domain playing a major role in controlling plant growth. While phloem phenotypes are not exacerbated in higher-order mutants, plant growth vigour is nevertheless more severely impacted than in ops opl2. Our results suggest a novel role of the OPS/OPL genes in broadly controlling plant growth and development, potentially through the modulation of meristematic activity via brassinosteroid pathways.