Abstract
The brassinosteroid (BR) signaling module is a central regulator of plant morphogenesis, as indicated by the large number of BR-responsive cell wall-related genes and the severe growth defects of BR mutants. Despite a detailed knowledge of the signaling components, the logic of this auto-/paracrine signaling module in growth control remains poorly understood. Recently, extensive cross-talk with other signaling pathways has been shown, suggesting that the outputs of BR signaling, such as gene-expression changes, are subject to complex control mechanisms. We previously provided evidence for a role of BR signaling in a feedback loop controlling the integrity of the cell wall. Here, we identify the first dedicated component of this feedback loop: a receptor-like protein (RLP44), which is essential for the compensatory triggering of BR signaling upon inhibition of pectin de-methylesterification in the cell wall. RLP44 is required for normal growth and stress responses and connects with the BR signaling pathway, presumably through a direct interaction with the regulatory receptor-like kinase BAK1. These findings corroborate a role for BR in controlling the sensitivity of a feedback signaling module involved in maintaining the physico-chemical homeostasis of the cell wall during cell expansion.
Highlights
The brassinosteroid (BR) signaling module is a central regulator of plant morphogenesis, as indicated by the large number of BRresponsive cell wall-related genes and the severe growth defects of BR mutants
To facilitate the identification of putative components involved in this pathway, we made use of plants that showed a strong BRmediated compensatory response to cell wall perturbation induced by the ectopic expression of a pectin methylesterase inhibitor (PMEIox) [14]
Using map-based cloning, we identified a mutation associated with the cnu2 phenotype causing a premature stop codon in RLP44 [18], which encodes a receptor-like protein with a predicted signal peptide, a leucine-rich repeat (LRR)-type extracellular domain, a transmembrane region, and a short cytoplasmic domain (Fig. 1B)
Summary
The brassinosteroid (BR) signaling module is a central regulator of plant morphogenesis, as indicated by the large number of BRresponsive cell wall-related genes and the severe growth defects of BR mutants. RLP44 is required for normal growth and stress responses and connects with the BR signaling pathway, presumably through a direct interaction with the regulatory receptor-like kinase BAK1 These findings corroborate a role for BR in controlling the sensitivity of a feedback signaling module involved in maintaining the physicochemical homeostasis of the cell wall during cell expansion. The abiotic and biotic environment can potentially change the cross-linking pattern of cell wall polymers and influence the extensibility of the cell wall In this context, the state of the wall has to be constantly monitored and information has to be relayed to the cytosol to regulate cell wall biosynthesis and remodeling in response to developmental and environmental cues [2].
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