Gene silencing of barley P23k involved in secondary wall formation causes abnormal tiller formation and intercalary elongation

Abstract

P23k is a monocot-unique protein that is highly expressed in barley. Our previous loss-of-function studies in barley leaves indicated that P23k, localized to tissues where cell wall polysaccharides accumulate, might contribute to secondary wall formation in the leaf. However, the P23k loss-of-function analysis was limited to the leaf, which is a vegetative organ. Considering the involvement of P23k in secondary wall formation, a dramatically altered phenotype is expected in the stem of P23k gene-silenced barley, where marked secondary wall deposition occurs during the reproductive growth stage. To test this hypothesis, barley striped mosaic virus-based virus-induced gene silencing of P23k was performed. Abnormal tiller formation and arrested intercalary elongation were observed in P23k-silenced barley. From these results, we speculated that cell wall architecture was altered by P23k gene silencing. Consistent with this idea, we observed a marked decrease in the amount of cell wall polysaccharides stained with calcofluor and down-regulation of the cellulose synthase-like CslF6 gene involved in (1,3;1,4)-β-D-glucan synthesis. Taken together, these results suggest that P23k is possibly involved in determining secondary wall architecture and contributes to tiller formation and intercalary elongation in barley.