Background
The MYB transcription factor family is one of the largest transcriptional factor families in plants and plays a multifaceted role in plant growth and development. However, MYB transcription factors involved in pathogen resistance in apple remain poorly understood.
Results
We identified a new MYB family member from apple, and named it
MdMYB30. MdMYB30
was localized to the nucleus, and was highly expressed in young apple leaves. Transcription of
MdMYB30
was induced by abiotic stressors, such as polyethylene glycol and abscisic acid. Scanning electron microscopy and gas chromatograph–mass spectrometry analyses demonstrated that ectopically expressing
MdMYB30
in Arabidopsis changed the wax content, the number of wax crystals, and the transcription of wax-related genes.
MdMYB30
bound to the
MdKCS1
promoter to activate its expression and regulate wax biosynthesis.
MdMYB30
also contributed to plant surface properties and increased resistance to the bacterial strain
Pst
DC3000. Furthermore, a virus-based transformation in apple fruits and transgenic apple calli demonstrated that
MdMYB30
increased resistance to
Botryosphaeria dothidea
. Our findings suggest that
MdMYB30
plays a vital role in the accumulation of cuticular wax and enhances disease resistance in apple.
Conclusions
MdMYB30
bound to the
MdKCS1
gene promoter to activate its transcription and regulate cuticular wax content and composition, which influenced the surface properties and expression of pathogenesis-related genes to resistance against pathogens. MdMYB30 appears to be a crucial element in the formation of the plant cuticle and confers apple with a tolerance to pathogens.
Electronic supplementary material
The online version of this article (10.1186/s12870-019-1918-4) contains supplementary material, which is available to authorized users.
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.
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. MdICS1 was induced by B. dothidea and enhanced the resistance to B. dothidea. MdICS1 promoter analysis indicated that the W‐box was vital for the response to B. dothidea treatment. MdWRKY15 was found to interact with the W‐box using yeast one‐hybrid screening. Subsequently, the interaction was confirmed by EMSA, yeast one‐hybrid, ChIP‐PCR, and quantitative PCR assays. Moreover, luciferase and GUS analysis further indicated that MdICS1 was transcriptionally activated by MdWRKY15. Finally, we found the function of MdWRKY15 in the resistance to B. dothidea was partially dependent on MdICS1 from the phenotype of transgenic apples and calli. In summary, we revealed that MdWRKY15 activated the transcription of MdICS1 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.
Salicylic acid (SA) is closely related to disease resistance of plants. WRKY transcription factors have been linked to the growth and development of plants, especially under stress conditions. However, the regulatory mechanism of WRKY proteins involved in SA production and disease resistance in apple is not clear. In this study, MdPBS3.1 responded to Botryosphaeria dothidea and enhanced resistance to B. dothidea. Electrophoretic mobility shift assays, yeast one-hybrid assays, and chromatin immunoprecipitation and quantitative PCR demonstrated that MdWRKY46 can directly bind to a W-box motif in the promoter of MdPBS3.1. Glucuronidase transactivation and luciferase analysis further showed that MdWRKY46 can activate the expression of MdPBS3.1. Finally, B. dothidea inoculation in transgenic apple calli and fruits revealed that MdWRKY46 improved resistance to B. dothidea by the transcriptional activation of MdPBS3.1. Viral vector-based transformation assays indicated that MdWRKY46 elevates SA content and transcription of SA-related genes, including MdPR1, MdPR5, and MdNPR1 in an MdPBS3.1-dependent way. These findings provide new insights into how MdWRKY46 regulates plant resistance to B. dothidea through the SA signaling pathway.
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