Calcium binding by arabinogalactan polysaccharides is important for normal plant development (Plant Cell)

Arabinogalactan proteins (AGPs) are a class of apoplastic carbohydrate-binding proteins with a carbohydrate portion that can also bind to calcium (Ca²⁺) ions in a pH-dependent manner. Here, Lopez-Hernandez and colleagues have probed the role of AGPs and the functional significance of their Ca²⁺-binding using mutants deficient in enzymes required for the assembly of carbohydrate moieties. Analysis of the mutants revealed a compromise in the composition of carbohydrates bound to AGPs, a reduction in Ca²⁺ binding, and severe growth defects in higher-order mutants. Interestingly, the growth defects, including trichome branching and de-etiolation, seemed to be dependent on external Ca²⁺ concentration. Further, hydrogen peroxide-induced Ca²⁺ signals were also attenuated in the mutant plants, which showed altered cell-to-cell movement of the Ca²⁺ signal. Thus, the ability of AGPs to bind Ca²⁺ may underlie several development aspects of plants and may also contribute to stress-induced cytosolic Ca²⁺ signaling. The authors suggest that AGPs act as extracellular reservoirs of Ca²⁺, which can accumulate Ca²⁺ and release it into the cytosol in case of stress conditions depending on changes in apoplastic pH. (Summary by Pavithran Narayanan @pavi_narayanan) Plant Cell 10.1105/tpc.20.00027