Arm-repeat proteins function during diverse aspects of plant development and morphogenesis, processes controlled by multiple intracellular signalling pathways. Plant Arm proteins function in gibberellin (GA) and abscisic acid (ABA) signalling, in addition to signalling through receptor kinases with as-yet unknown ligands. Interestingly, all plant Arm proteins so far implicated in developmental signal transduction are putative ubiquitin ligases, highlighting the key importance of regulated protein degradation during development. It is tempting to speculate that many hormones use plant Arm proteins for aspects of their signal transduction, to allow diverse cell type-specific responses.
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