[Analysis of the response of the OsLFNR2 gene in rice to shading treatment].

In a previous study, quantitative trait locus (QTL) mapping identified the gene LOC_Os06g01850, which is associated with oxidative damage resistance in rice, and it was further confirmed to encode a chloroplast-localized ferredoxin-NADP+ oxidoreductase, namely OsLFNR2. To gain deeper insight into the function of OsLFNR2, bioinformatics approaches were employed in the present study to determine its evolutionary conservation and to predict cis-acting elements related to stress and light responses in its promoter region. Using the japonica rice cultivar Nipponbare (Oryza sativa L. ssp. japonica) as the experimental material, quantitative real-time polymerase chain reaction (qRT-PCR) was performed to determine the expression differences of OsLFNR2 in various tissues of Nipponbare and its expression dynamics under shading treatment. Furthermore, two knockout mutants with different mutation types were generated for this gene and subjected to shading treatment. The data showed that OsLFNR2 was most highly expressed in the leaf sheath and was barely expressed in non-photosynthetic tissues, and it was confirmed that its expression was significantly down-regulated under shading conditions. Compared with the wild type, the two knockout mutants with different mutation types exhibited lower seedling height but higher ribulose-1,5-bisphosphate carboxylase (Rubisco) activity and chlorophyll content. After shading treatment, the mutants displayed stronger stress adaptability relative to the wild type, suggesting that OsLFNR2 may function as a negative regulator in the response of rice to shading treatment. The results of physiological index detection indicated thatthe mutants maintained lower Rubisco activity but markedly enhanced antioxidant enzyme activities. The qRT-PCR results showed that OsLFNR2 was involved in the maintenance of chloroplast homeostasis under shading stress; compared with the wild type, the expression levels of most genes related to chloroplast development and chlorophyll biosynthesis were up-regulated to varying degrees in the mutants. The loss of OsLFNR2 may enhance the efficiency of reactive oxygen species scavenging in the mutants under shading treatment while maintaining chloroplast protein homeostasis by down-regulating photosynthetic efficiency, ultimately enhancing the adaptability of the mutants to shading environments.