Molecular mechanisms regulating mesophyll conductance under severe water stress for water-saving drought-resistant rice in wetting-drying alternate irrigation

Abstract

Water-saving and drought-resistant rice (WDR) is a new type of rice variety. Maintenance of high mesophyll conductance ( g m ) is one of the main factors promoting high photosynthetic production in WDR in water stress. We hypothesized that suitable irrigation regimes before water stress could further improve g m of WDR by activating some key genes in water stress. Therefore, WDR cultivar (HY73) and drought-sensitive cultivar (HLY898) were used for comparative studies. Three irrigation regimes were set before heading stage. Severe water stress was applied at heading for both cultivars in the three water treatments. RNA-seq, weighted gene co-expression network analysis, and protein interaction analysis were adopted to screen key genes maintaining high g m of WDR in water stress. It was found that when subjected to mild wetting-drying alternate irrigation, cultivar HY73 plants showed the highest net photosynthesis rate ( P n ), g m , and SPAD value, as compared with the P n , g m, and SPAD exhibited by all other combinations in severe water stress. A total of 3071 differentially expressed genes (DEGs) were clustered in 3 modules named midnightblue (734 DEGs), blue (921 DEGs), and turquoise (1416 DEGs) in severe water stress. Weighted gene co-expression network analysis revealed that the three modules (midnightblue, blue, and turquoise) were significantly correlated with g m ( p <0.05). Genes in the midnightblue module were the only enriched genes and positively regulated g m in the photosynthesis process ( p <0.05). In the midnightblue module, 11 hub genes were screened using the co-expression networks method. It was found that OsCSP41B , OsPGLP1A , OsLHCA5 , and OsGSTU6 genes had similar variation trends with g m among the 11 hub genes in the three water treatments for both cultivars. Results of the present study showed that OsLHCA5 and OsCSP41B genes were significantly up-regulated in cultivar HY73, as compared with cultivar HLY898 in water stress conditions, especially in mild wetting-drying alternate irrigation ( p <0.05). Therefore, it was evident that high expressions of OsLHCA5 and OsCSP41B genes are important mechanisms for maintaining great g m and improving drought-resistance abilities in WDR in water stress. Mild wetting-drying alternate irrigation has positive effects to increasing expression level of OsLHCA5 and OsCSP41B genes in WDR in severe water stress. • High drought-resistance ability in WDR could be related to greater endurance by activating more differential genes. • The formation of high photosynthetic production potential may be the result of the synergistic effects of g m and energy distribution in thylakoid membrane for WDR in severe drought. • OsLHCA5 and OsCSP41B genes could be candidate genes for the synergistic regulation of g m and energy allocation in thylakoid membrane to obtain high photosynthetic production potential in drought.