Proteomic analysis of positive influence of alternate wetting and moderate soil drying on the process of rice grain filling

Rice ( Oryza sativa L.) is one of the most important crops in the world to feed ever increasing world population. An increase in output of rice crop per unit is imminent. Alternate wetting and moderate soil drying (AWD) irrigation technology has been recommended as a good practice method to improve grain filling of rice crop at late growing stages. Physiological, molecular and agronomic parameters were adopted to elucidate the role of rice stem and sheath under AWD treatment as compared to the conventional irrigation during the grain filling stage. AWD treatment significantly increased stem and sheath dry weight, carbohydrate reserves and their remobilization to the grain, especially inferior spikelet grains. The results showed that the transport and conversion rate of the stem and sheath photoassimilates increased by 9.87 and 8.37%, respectively. Furthermore, protein expression profiles of the stem and sheath at 10, 20 and 30 days after flowering were analyzed. We examined 220 differentially expressed proteins, and successfully identified 166 proteins, including 71 proteins in the stem and 95 proteins in the sheath involved in thirteen important functional groups. Our results suggest that the AWD treatment at the rice grain filling stage is highly conducive to trigger the mobilization of the N assimilates from leave and root to the stem and sheath, and then promotes to remobilize the reserves to the grain through coordinately expressed proteins involved in photosynthesis, systematic senescence, oxidative stress defense, signal transduction and other metabolisms. This study reveals the metabolic mechanism of the stem and sheath in response to AWD at grain filling stage, and provides theoretical evidence for better quality control and scientific improvement of rice in practice.