Cuticle Composition Analysis And Transcriptome Study Of Pepper Keratin Deficiency Mutant "Pcd1"

The cuticle acts as a barrier to protect the aerial organs of plants and is located on the outer surface of the outermost cell wall of epidermal cells.The cuticle covering the surface of the pepper fruit can limit the water loss of the fruit,thereby maintaining the quality of the fruit after harvest.In order to clarify the structure,chemical composition and biosynthetic pathways of the cuticle in pepper,many researchers have carried out research related to the cuticle,but the genes and biological pathways related to the synthesis of pepper cuticle are still unclear.This study mainly introduces the research progress of the cuticles,including the composition of cuticles,the synthetic pathway and genes related to its synthesis.The post-harvest microstructure observation and physiological analysis of pepper "8214" and "Pcd1" were performed by paraffin section,scanning electron microscope,post-harvest moisture loss and toluidine blue staining;Qualitative and quantitative determination of wax components and cutin monomers in fruits of "8214" and "Pcd1" at different periods by GC-MS method;With the help of transcriptome technology,the differentially expressed genes and their functions between "8214" and "Pcd1" fruits at different periods were explored,so as to lay the foundation for the selection of excellent pepper varieties.The main research results are as follows:(1)The microstructure of the fruit epidermis shows that the thickness of the cuticle of "8214" was higher than that of "Pcd1";the surface of the peel of "8214" was smooth and the cell structure was full and tangible,the thickness of the cuticle and the gap between the outermost cells of the fruit epidermis increase with the development period.While the "Pcd1" peel surface shrinks and the cell structure is irregular,showing a water shortage state,the growth during the development period does not have much effect on the structure of the epidermal cells and the thickness of the stratum corneum.The post-harvest water loss measurement results show that the water loss rate of the "Pcd1" fruit after harvest is about twice that of the "8214".The permeability analysis of the cuticle found that the penetration of "Pcd1" fruit was greater than that of "8214".(2)The analysis of cuticle composition found that there were 6 more wax components on the epidermis of "8214" fruit than "Pcd1",the total wax content was 3 times higher,4 more types of keratin monomer components,and the total keratin content was 3 times higher;the total content of wax and keratin of the same material increases with the growth of fruit development period.(3)Using transcriptome sequencing technology,3781 differentially expressed genes(DEGs)were identified in the three developmental stages of "8214" and "Pcd1" pepper fruits,and about 40% of the DEGs were down-regulated in the cuticles deficiency mutant "Pcd1".These DEGs involve biological processes such as lipid metabolism,fatty acid extension,sucrose and starch metabolism,and linoleic acid metabolism,etc.Although the cuticle is prevalent in land plants and there is a clear connection between its structure and the resistance of plants to the pressure of the terrestrial environment,the mechanism of its biosynthesis remains unclear.This study provides a reference for further exploring the metabolic pathways or specific functions of a gene related to adversity and cuticle synthesis,and also lays the foundation for breeding excellent pepper varieties.