Repression of OsEXPA3 Expression Leads to Root System Growth Suppression in Rice

摘要

Expansins are cell-wall-loosening proteins known to be involved in a wide range of physical processes during plant development. OsEXPA3, a rice a-expansin gene, was found to be preferentially expressed in the root and highly induced by NaCl, while suppressed by nitrate (N) and phosphate (Pi) starvation. Repression of OsEXPA3 expression by RNA interference (RNAi) in rice (Oryza sativa L.) severely impaired the growth of the root system. A significant reduction in the primary root length and lateral root density was observed in 1-wk-old OsEXPA3-RNAi lines at seedling stage, and the total size and density of the root system was clearly decreased in 1-mo-old plants. Besides, the root hair of RNAi seedlings was clearly shorter than that of wildtype plants. Moreover, RNAi plants exhibited clearly inhibited growth, which is mostly attributed to the poorer root system architecture. Further study indicated that the cell length of root vascular bundles and cell growth in suspension cultures in OsEXPA3-RNAi lines decreased significantly, which revealed the cellular basis for OsEXPA3-mediated rice root growth. Further, the cell-wall mechanical properties of suspension cells probed by atomic force microscopy (AFM) showed that repression of OsEXPA3 led to a significant increase in cell-wall stiffness, and cell-wall polymer compositions revealed by Fourier transform infrared (FTIR) spectra were also strongly changed. Taken together, the results suggest that OsEXPA3 is required for root system development in rice and involved in mediating root growth by mediating cell-wall loosening.