OsEXPB2, a β-expansin gene, is involved in rice root system architecture

Abstract

Expansins are cell wall loosening proteins which generally play important roles as endogenous regulators in plants. Here we report a rice (Oryza sativa L.) β-expansin gene, OsEXPB2, which encodes a 28.6-kDa protein of 261 amino acids. Sequence alignment revealed that the N-terminal and C-terminal of OsEXPB2 share six discontinuous cysteine residues and four intermittent tryptophan residues, respectively. The OsEXPB2 promoter contains conserved root hair-specific elements. Subcellular localization assay revealed that OsEXPB2 was localized in the cell wall. Analysis of spatial and temporal expression patterns demonstrated that OsEXPB2 was predominantly expressed in root of rice. OsEXPB2 expression levels were up-regulated by abiotic stresses, such as phosphate or iron deficiency, and also suppressed by abscisic acid. A clear difference was observed between RNA interference (RNAi) lines and wild-type in root system architecture and plant height, and the suppression of OsEXPB2 resulted in a visible alteration of the width of the leaf blade. Anatomical analysis found that the cell size of root cortical cells in OsEXPB2-suppressed lines was significantly smaller than that of their counterparts in wild-type plants. Furthermore, cryo-scanning electron microscopy analysis showed that the development of root hair was suppressed in RNAi lines. All these results suggest that OsEXPB2 is a root-predominant gene with a key role in root-hair formation and has the potential to be utilized in transgenic root breeding to improve abiotic stress tolerance.