The involvement of expansins in responses to phosphorus availability in wheat, and its potentials in improving phosphorus efficiency of plants

Phosphorus (P) is a critical macronutrient required for numerous functions in plants and is one of the limiting factors for plant growth. Phosphate availability has a strong effect on root system architecture. Expansins are encoded by a superfamily of genes that are organized into four families, and growing evidence has demonstrated that expansins are involved in almost all aspects of plant development, especially root development. In the current study, we demonstrate that expansins may be involved in increasing phosphorus availability by regulating the growth and development of plant roots. Multiple expansins (five α- and nine β-expansin genes) were up- or down-regulated in response to phosphorus and showed different expression patterns in wheat. Meanwhile, the expression level of TaEXPB23 was up-regulated at excess-P condition, suggesting the involvement of TaEXPB23 in phosphorus adaptability. Overexpression of the TaEXPB23 resulted in improved phenotypes, particularly improved root system architecture, as indicated by the increased number of lateral roots in transgenic tobacco plants under excess-P and low-P conditions. Thus, these transgenic plants maintained better photosynthetic gas exchange ability than the control under both P-sufficient and P-deficient conditions.