Photosynthetic Physiological Regulation Mechanism of VIRESCENT-ALBINO LEAF 1 in Rice (Oryza sativa L.)

Improving photosynthetic potential and light use efficiency is a crucial way to increase rice yield. The virescent-albino leaf 1 ( val1 ) mutant, wild-type ‘Jinhui 10’ (WT), and VAL1 gene overexpression plants ( VAL1 -OE) were used to determine the physiological mechanisms of survival strategy in val1 mutant and improvement of photosynthetic potential in VAL1 -OE through investigating leaf photosynthetic characteristics, photoprotection processes and yield. The results showed that, compared with WT, the expressions of key genes in photosynthetic pathway and chlorophyll contents in val1 mutant were both significantly lower at the early growth stage and higher at the late growth stage. Besides, the photosynthetic electron transport rate, the quantum yield of photosystem II and I, and carboxylation efficiency in val1 mutant were significantly lower than those in WT at the early growth stage, but significantly higher at the late growth stage. Furthermore, the non-photochemical quenching (NPQ) of val1 mutant was significantly higher than WT, thereby optimizing the heat dissipation pathway on the basis of reducing the chlorophyll contents and light absorption at the early growth stage. The NPQ and cyclic electron flow (CEF) were significantly higher in val1 mutant than WT at the late growth stage, resulting in the improvements of light use efficiency and photosynthetic acclimation under both low and high light conditions. Compared with WT, the expressions of key genes in photosynthetic pathway and chlorophyll contents were significantly higher in VAL1 -OE. The photosynthetic electron transport rate, quantum yield of photosystem II and I, and the carboxylation efficiency in VAL1 -OE were significantly higher than those in WT, improving light use efficiency and carboxylation efficiency of VAL1 -OE. Overall, the val1 mutant survived by the optimal plant phenotype and leaf photoprotection pathway at the early growth stage, and improved photosynthetic potential and light use efficiency at the late growth stage. VAL1 -OE improved light absorption by optimizing the dissipation pathway of excess light energy so as to increase light use efficiency and carboxylation efficiency. Cultivating phenotypic materials with high leaf area on the basis of high photosynthesis rate in VAL1 -OE could be a breakthrough in high photosynthetic efficiency rice breeding.