Multifaceted roles of rice ABA/stress-induced intrinsically disordered proteins in augmenting drought resistance.

Water deficit stress causes devastating loss of crop yield worldwide. Improving crop drought resistance has become an urgent issue. Here we report that a group of abscisic acid (ABA)/drought stress-induced monocot-specific, intrinsically disordered, and highly proline-rich proteins, REPETITIVE PROLINE-RICH PROTEINS (RePRPs), play pivotal roles in drought resistance in rice seedlings. Rice ectopically expressing RePRPs outlive wild-type rice under extreme drought conditions primarily due to two underlying mechanisms. First, RePRP reduces water loss by decreasing stomata conductance in shoot and enhances levels of extracellular water barriers such as lignin and suberin, primarily in the root vascular bundle. Genes involved in lignin biosynthesis, especially the wall-bound peroxidase responsible for the final assembly of the lignin network, were induced by RePRP. Second, overexpression of RePRP leads to lowered root osmotic potential. Root cell osmotic pressure is more negative in rice plants overexpressing RePRP2 than wild-type plants, and the concentration of a key osmolyte, proline, is enhanced. Hence, ABA/stress-induced RePRP expression leads to several beneficial traits of drought resistance, including lower water loss upon dehydration and higher root water use efficiency under drought conditions. These unique stress proteins may be an important target for technology development in enhancing drought stress resistance in cereals.