Chemical composition and morphology of apple cuticular wax during fruit growth and development

Abstract Cuticular wax covers the surface of the apple epidermis and plays an important role in water loss and pathogen resistance.However,little is known about wax biosynthesis during apple fruit development.In this study,the morphological structure and chemical composition of wax and the transcription patterns of wax-related genes were investigated in the'Red Delicious'and'Golden Delicious'cultivars.The results showed that accumulation of the waxy layer was synchronized with enlargement and maturation of fruit.The crystal structure,major chemical components(very long chain fatty acids and triterpenes)of wax and the expression levels of wax-related genes varied significantly 90 days after flowering(DAF),indicating that the critical period for biosynthesis of cuticular wax was about 90 DAF.This finding is valuable for further study of the regulatory mechanism of wax biosynthesis at both the molecular and physiological levels.

MdWRKY15 improves resistance of apple to Botryosphaeria dothidea via the salicylic acid-mediated pathway by directly binding the MdICS1 promoter^FA

Isochorismate synthase(ICS) plays an essential role in the accumulation of salicylic acid(SA) and plant disease resistance. Diseases caused by Botryosphaeria dothidea affect apple yields. Thus, it is important to understand the role of ICS1 in disease resistance to B. dothidea in apple. In this study, SA treatment enhanced the resistance to B. dothidea. Md ICS1 was induced by B. dothidea and enhanced the resistance to B. dothidea. Md ICS1 promoter analysis indicated that the W-box was vital for the response to B. dothidea treatment. Md WRKY15 was found to interact with the W-box using yeast one-hybrid screening. Subsequently, the interaction was confirmed by EMSA, yeast one-hybrid, Ch IP-PCR, and quantitative PCR assays. Moreover, luciferase and GUS analysis further indicated thatMd ICS1 was transcriptionally activated by Md WRKY15. Finally, we found the function of Md WRKY15 in the resistance to B. dothidea was partially dependent on Md ICS1 from the phenotype of transgenic apples and calli. In summary, we revealed that Md WRKY15 activated the transcription of Md ICS1 by directly binding to its promoter to increase the accumulation of SA and the expression of disease-related genes, thereby resulting in the enhanced resistance to B.dothidea in the SA biosynthesis pathway.