Preliminary Studies About The Reasons Of Specific Expression Of Cell Wall Loosening Genes In Lettuce Endosperm Cap

Among the cellwall looseing process,enzymatic degradation mechanisms（Cellulase,Hemicellulase,Pectin-degrading enzyme,etc.）and non-enzymatic degradation mechanisms（Expansion and Reactive Oxygen Species,ROS）play an important role in the process of endosperm cell wall loosening.In the genes encoding the degradation of endosperm cap cell wall,some are expressed specifically in the endosperm cap of germinating seeds,so they are called Endosperm cap-specific genes.About the tissue specific expression gene,researcher proposed two hypotheses:the fixed-point mechanical contact（Touch）of endosperm cap caused by the elongation growth of radicle,and the fixed-point secretion of gibberellin（GA）in endosperm cap.Lettuce（Lactuca sativa）is a widely cultivated vegetable crop and a model plant to study the mechanism of seed germination.The germination of lettuce seeds requires both radicle elongation and endosperm weakening.Based on the tissue-specificity expression hypothesis of cell wall loosening,the endosperm cap of lettuce seed was used as the experimental material,and the experimental conditions were designed to investigate the expression characteristics of enzyme and non-enzyme factors in the endosperm cap of lettuce.Some promoters of cell wall loosening genes were cloned,and GUS reporter gene was connected to construct the expression vector to preliminarily explore the expression characteristics of cell wall loosening genes in the endosperm cap of lettuce.The main conclusions of this paper are as follow:1)The results showed that“Touch”and GA increased the activities of mannanase,superoxide radical and hydrogen peroxide in endosperm cap of lettuce seeds;2)The expression level of LsMan6、LsRbohE、LsPOD63-like1 genes in the isolated endosperm cap after coculture with GA₃ or isolated embryo was higher than that of coculture in water;3)The expression vector:LsMan6,LsRbohE,LsPOD63-like1,LsPOD42 was constructed and the transgenic plants were obtained.Through the above experiments,it is concluded that:The specific expression of LsMan6、LsRbohE、LsPOD63-like1 in endosperm cap of lettuce is related to the fixed Touch and secretion of GA in endosperm cap.