Response Regulator 6 (ARR6) Modulates Plant Cell-Wall Composition and Disease Resistance.

The cytokinin signaling pathway, which is mediated by response regulator (ARR) proteins, has been involved in the modulation of some disease-resistance responses. Here, we describe novel functions of ARR6 in the control of plant disease-resistance and cell-wall composition. Plants impaired in function () were more resistant and susceptible, respectively, to the necrotrophic fungus and to the vascular bacterium , whereas plants that overexpress showed the opposite phenotypes, which further support a role of in the modulation of disease-resistance responses against these pathogens. Transcriptomics and metabolomics analyses revealed that, in plants, canonical disease-resistance pathways, like those activated by defensive phytohormones, were not altered, whereas immune responses triggered by microbe-associated molecular patterns were slightly enhanced. Cell-wall composition of plants was found to be severely altered compared with that of wild-type plants. Remarkably, pectin-enriched cell-wall fractions extracted from walls triggered more intense immune responses than those activated by similar wall fractions from wild-type plants, suggesting that pectin fraction is enriched in wall-related damage-associated molecular patterns, which trigger immune responses. This work supports a novel function of in the control of cell-wall composition and disease resistance and reinforces the role of the plant cell wall in the modulation of specific immune responses.