Proteomic Analysis Reveals The Effect Of Chlorophyll Metabolism On The Color Change Of Wucai Leaves

Wucai(Brassica campestris L.)is a subspecies of Chinese cabbage(Brassica pekinensis).In this study,two species of Wucai(Brassica campestris L.)were used as experimental materials,and their names were W7-2 and W7-1.During the growth and development of W7-2,the color of the inner leaves will gradually develop from green to yellow,but the outer leaves are still green.The non-color-changing green leaf phenotype W7-1 was used as a control.Under the condition of cold domestication,the color difference,pigment content,chloroplast ultrastructure,proteomic comparison,chlorophyll biosynthesis and photosynthetic products of W7-2 and W7-1 during the whole color transition period were studied and analyzed.The main results are as follows:1.Compared with the color values of W7-1,the color L*(brightness)and color b*(yellow)of W7-2 leaves are significantly higher than that of W7-1.Moreover,in the whole growth process of W7-2,the color b* and color L* increased significantly with the increase of the days after planting(d).2.Compared with W7-1,the contents of chlorophyll a and chlorophyll b in W7-2were significantly reduced in five developmental stages(13,21,29,37 and 45 d).However,during the whole period of W7-1,there was no significant difference in the contents of Chlorophyll a and Chlorophyll b.3.At 29 days after planting(after discoloration),the chloroplast ultrastructure of W7-2 was irregular,the particle accumulation density was low,and there were more starch grains and osmiophilic particles,and the thylakoid layer structure became thinner and distorted.4.According to the changes in leaf color of the two genotypes,iTRAQ-based proteomic comparative analysis was conducted on 21 and 29 d,respectively.A total of1409 proteins were identified,and 218 differentially expressed proteins(DEPs)were identified by comparing W7-2 and W7-1 at the two developmental stages.Differentially expressed proteins are mainly involved in chlorophyll biosynthesis,photosynthesis,carbohydrate metabolism,ribosome metabolism and post-translational modification.NADPH-protochlorophyllide oxidoreductase(PORB)and Mgprotoporphyrin IX chelatase 1(CHLI1)are key enzymes involved in chlorophyll biosynthetic.These proteins are involved in leaf color changes of W7-2,and they help to reduce chlorophyll content and chlorophyll metabolism intermediates.5.At 45 d,the levels of ALA,PBG,Proto IX,Mg-Proto IX and Pchlide in W7-2significantly decreased,while the contents of these intermediate metabolites in W7-1increased slightly or did not change significantly after different days after planting.6.During the whole color transition period,the soluble sugar contents of the two varieties showed a trend of gradually accumulating,while the starch content showed a characteristic of first rising and falling.The contents of soluble sugar and starch in W7-2 were significantly higher than that in W7-1.