Abstract
The plant cell wall is a highly dynamic structure that changes in response to both environmental and developmental cues. It plays important roles throughout plant growth and development in determining the orientation and extent of cell expansion, providing structural support and acting as a barrier to pathogens. Despite the importance of the cell wall, the signaling pathways regulating its function are not well understood. Two partially redundant leucine-rich-repeat receptor-like kinases (LRR-RLKs), FEI1 and FEI2, regulate cell wall function in Arabidopsis thaliana roots; disruption of the FEIs results in short, swollen roots as a result of decreased cellulose synthesis. We screened for suppressors of this swollen root phenotype and identified two mutations in the putative mitochondrial pyruvate dehydrogenase E1α homolog, IAA-Alanine Resistant 4 (IAR4). Mutations in IAR4 were shown previously to disrupt auxin homeostasis and lead to reduced auxin function. We show that mutations in IAR4 suppress a subset of the fei1 fei2 phenotypes. Consistent with the hypothesis that the suppression of fei1 fei2 by iar4 is the result of reduced auxin function, disruption of the WEI8 and TAR2 genes, which decreases auxin biosynthesis, also suppresses fei1 fei2. In addition, iar4 suppresses the root swelling and accumulation of ectopic lignin phenotypes of other cell wall mutants, including procuste and cobra. Further, iar4 mutants display decreased sensitivity to the cellulose biosynthesis inhibitor isoxaben. These results establish a role for IAR4 in the regulation of cell wall function and provide evidence of crosstalk between the cell wall and auxin during cell expansion in the root.
Highlights
Cell expansion plays a critical role in plant growth and development
We show that mutations in the previously characterized IAA-Alanine Resistant 4 (IAR4) gene, encoding a putative mitochondrial E1a pyruvate dehydrogenase subunit, suppress the defects in root anisotropic cell expansion exhibited by fei1 fei2
The F1 of a backcross to the parental fei1 fei2 line displayed a non-suppressed phenotype, and the suppressor phenotype segregated consistent with 3 non-suppressed: 1 suppressed ratio in the F2 progeny of this backcross, consistent with shou2 acting as a single locus, recessive mutation
Summary
Cell expansion plays a critical role in plant growth and development. The direction and extent to which cells expand is controlled by the rigid, yet highly dynamic cell wall. The architecture of the cell wall permits longitudinal cell elongation while restricting radial expansion, which leads to highly asymmetric, anisotropic growth [1,2,3,4]. Together with a relatively small number of structural proteins, this matrix of polysaccharides lends the wall the strength and rigidity that is required for structural support and plant defense, while simultaneously allowing cells to expand as plants grow and develop [5]. Wall polymers are actively remodeled and rearranged and their synthesis is altered in response to both developmental and environmental cues [6]. Despite a crucial role in the maintenance of plant cell wall function, our current understanding of the components and mechanisms involved in the perception of and response to regulatory input from the wall remains poorly understood
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