The MdWRKY31 transcription factor binds to the MdRAV1 promoter to mediate ABA sensitivity

The phytohormone abscisic acid(ABA)is a major element involved in apple(Malus domestica)production because of its role in seed germination and early seedling development.The WRKY family,which is one of the largest families of transcription factors,plays an important role in ABA signaling in plants.However,the underlying molecular mechanisms of WRKY-mediated ABA sensitivity in apple are poorly understood.A genome-wide transcriptome analysis indicated that MdWRKY31 is a key factor induced by ABA.Quantitative real-time PCR showed that MdWRKY31 is induced by ABA in response to PEG4000,which is used to simulate drought.As a transcription factor,MdWRKY31 is localized in the nucleus.Ectopic expression of MdWRKY31 in Arabidopsis and Nicotiana benthamiana enhanced plant sensitivity to ABA.Overexpression of MdWRKY31 in apple roots and apple calli increased sensitivity to ABA,whereas repression of MdWRKY31 reduced sensitivity to ABA in the roots of‘Royal Gala’.Electrophoretic mobility shift assays,chromatin immunoprecipitation PCR,and yeast one-hybrid assays indicated that MdWRKY31 directly binds to the promoter of MdRAV1.Expression analyses of transgenic apple calli containing MdWRKY31 and pMdRAV1::GUS implied that MdWRKY31 represses the expression of MdRAV1.We also found that MdRAV1 binds directly to the promoters of MdABI3 and MdABI4 and repressed their expression.Our findings reveal a new important regulatory mechanism of MdWRKY31-MdRAV1-MdABIs in the ABA signaling pathway in apple.

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.