Study On The Mechanism Of S1MYB4 Regulating Tomato Lignin Synthesis

Tomato(Solanum lycopersicum L.)is an important vegetable crop that is widely grown in China.Lignin is the main component of xylem cells,and has important biological functions such as support,protection and transport,and plays an important role in the development of tomato stems.The hydrophobic properties of lignin prevent water loss,and optimize the absorption and transfer of water and mineral elements through vascular tissue,affect plant growth and development,and thus have an important impact on tomato yield.Lignin biosynthesis has been reported to be regulated by the R2R3-MYB transcription factor.This study explored the function of Sl MYB4 in the regulation of lignin synthesis,and carried out a preliminary analysis of its regulation mechanism,and obtained the following research results:1.Tissue expression profiling showed that Sl MYB4 was expressed in all tissues of tomato,and the highest expression was found in roots and stalks.The expression of Sl MYB4 decreased gradually during fruit ripening,and it was hardly expressed in mature fruits.2.The identification of transgenic function showed that over-expression of Sl MYB4 resulted in thicker stems,and paraffin sections showed that the xylem cells of Sl MYB4 over-expressing plants were significantly larger.3.The determination of lignin content showed that the lignin content in the stem of Sl MYB4 over-expressing plants was significantly decreased,indicating that Sl MYB4 negatively regulated the synthesis of tomato lignin.4.The gene expression analysis showed that the expression levels of lignin synthesis related genes such as CCR,PAL,4CL and C4 H were significantly decreased in the stems of Sl MYB4 over-expressing plants,indicating that their expression was negatively regulated by Sl MYB4.5.Promoter analysis showed that the promoters of PAL1,4CL4,CCR2,COMT and other lignin synthesis related genes contained Sl MYB4 binding AC-II elements,yeast one-hybrid assay proved that Sl MYB4 could bind to PAL2,4CL4 promoter,indicating that Sl MYB4 negatively regulated the expression of these genes and then regulated the synthesis of lignin.6.Yeast one-hybrid and dual luciferase experiments showed that Sl MYB4 could not directly bind to the promoter of flavonoid-synthesizing key gene Sl CHS1.In Sl MYB4over-expressing lines,there was no significant change in the expression of Sl MYB12,and the expression of Sl CHS1 was decreased.There was no significant difference in flavonoid content,indicating that Sl MYB4 could not affect the accumulation of flavonoids in tomato leaves.7.Yeast two-hybrid experiments demonstrated that there was an interaction between Sl MYB4-p GADT7 and truncated Sl MYB12-BD4-p GADT7,and Sl MYB4 as well as Sl MYB12 may function in the form of complex.