Mechanism Of Low Silicon Rice Gene 1 (Lsi1) In Regulating Rice (Oryza Sativa L.) UV-B Resistance

Silicon (Si) is the second most abundant element in soil and plays an important role in plant growth and development; it has beneficial function in enhancing plant resistance to biotic and abiotic stresses. Rice is a typical Si-accumulating plant; Si contributes to enable the high and stable yield of rice and it is also able to protect rice from diseases, pest, lodging, drought condition etc. According to this paper, we found that rice cultured in Si-deficiency solution had lower gene transcript levels of phenylalanine ammonia lyase (PAL), photolyase, and lower contents of total phenolics and flavonoids in leaves than that in Si-containing solution. The same tendency was found in the case that the rice accession in the two hydroponic treatments was exposed to UV-B radiation. The results suggested that Si could positively regulate rice UV-B resistance. Further study has shown that the accumulation of Si in rice is controlled by low silicon rice gene 1(Lsi1), which encodes an aquaporin that belongs to a member of Nod26-like major intrinsic protein (NIP) subfamily. It suggests that Si uptake ability in rice is correlative to the gene expression level of Lsi1 in root.In order to further elucidate the regulatory mechanism of Lsi1 in the defense to enhanced UV-B radiation stress, we suppressed and overexpressed Lsi1 in UV-B resistance rice accession Lemont respectively. The results showed that transcript level of photolyase and PAL was increased in Lsi1-overexpressed transgenic lines of Lemont, but down-regulated in Lsi1-RNAi transgenic line of Lemont in the compared with their wild types (WT) under normal light condition. The expression level of the two genes in all entries was enhanced after UV-B radiation treatment, and it was the highest in Lsi1-overexpressed lines of Lemont, followed by their WT, and lowest in Lsi1-RNAi line of Lemont. The same tendency was found in the content of total phenolics and flavonoids. Further study by suppression subtractive hybridization (SSH) found that Lsi1 not only could regulate the expression of PAL and photolyase, but also could regulate detoxification-, resistance-, and photosynthesis-related genes etc through its positive feedback effect. The results were further confirmed in the overexpression of Lsi1 in Dular. The findings suggested that the regulation of silicon nutrient by enhancing/inhibiting expression of Lsi1 could effectively regulate UV-B tolerance in rice.