SUMMARY
Drought stress induces anthocyanin biosynthesis in many plant species, but the underlying molecular mechanism remains unclear. Ethylene response factors (ERFs) play key roles in plant growth and various stress responses, including affecting anthocyanin biosynthesis. Here, we characterized an ERF protein, MdERF38, which is involved in drought stress‐induced anthocyanin biosynthesis. Biochemical and molecular analyses showed that MdERF38 interacted with MdMYB1, a positive modulator of anthocyanin biosynthesis, and facilitated the binding of MdMYB1 to its target genes. Therefore, MdERF38 promoted anthocyanin biosynthesis in response to drought stress. Furthermore, we found that MdBT2, a negative modulator of anthocyanin biosynthesis, decreased MdERF38‐promoted anthocyanin biosynthesis by accelerating the degradation of the MdERF38 protein. In summary, our data provide a mechanism for drought stress‐induced anthocyanin biosynthesis that involves dynamic modulation of MdERF38 at both transcriptional and post‐translational levels.
Summary
Wounding stress leads to anthocyanin accumulation. However, the underlying molecular mechanism remains elusive. In this study, MdWRKY40 was found to promote wounding‐induced anthocyanin biosynthesis in association with MdMYB1 and undergo MdBT2‐mediated degradation in apple.
We found that MdMYB1, a positive regulator of anthocyanin biosynthesis, was essential for the wounding‐induced anthocyanin biosynthesis in apple. MdWRKY40 was identified as an MdMYB1‐interacting protein, and enhanced the binding of MdMYB1 to its target genes in response to wounding.
We found that MdBT2 interacted physically with MdWRKY40 and was involved in its degradation through the 26S proteasome pathway.
Our results demonstrate that MdWRKY40 is a key modulator in the wounding‐induced anthocyanin biosynthesis, which provides new insights into the regulation of wounding‐induced anthocyanin biosynthesis at both the transcriptional and post‐translational levels in apple.
As an important environment factor, light affects plant growth and development throughout life. B-BOX (BBX) proteins play key roles in the regulation of light signaling. Although the multiple roles of BBX proteins have been extensively studied in Arabidopsis, the research in apple is much less extensive. In this study, we systematically characterized the negative role of an apple BBX protein MdBBX37 in light signaling, including inhibiting anthocyanin biosynthesis and promoting hypocotyl elongation. We found that MdBBX37 interacted with MdMYB1 and MdMYB9, two key positive regulators of anthocyanin biosynthesis, and inhibited the binding of those two proteins to their target genes and, therefore, negatively regulated anthocyanin biosynthesis. In addition, MdBBX37 directly bound to the promoter of MdHY5, a positive regulator of light signaling, and suppressed its expression, and thus relieved MdHY5-mediated hypocotyl inhibition. Taken together, our investigations suggest that MdBBX37 is a negative regulator of light signaling in apple. Our study will provide reference for further study on the functions of BBX proteins in apple.
Summary
The molecular mechanism of leaf senescence in apple (Malus domestica) is still not fully understood. We used gene expression analysis and protein–protein interactions to decipher the relationships of abscisic acid (ABA) and two proteins, MdbHLH93 and MdBT2, in the senescence process.
We found that MdbHLH93 promoted leaf senescence and the expression of senescence‐related genes, which exhibited similar effects to ABA on leaf senescence. MdbHLH93 activated directly the transcription of MdSAG18.
We also found that an ABA‐responsive protein, MdBT2, interacted directly with MdbHLH93, and induced the ubiquitination and degradation of the MdbHLH93 protein, and thus delayed leaf senescence.
Our findings provide new insights into the regulatory network of leaf senescence through the functional interactions among ABA, MdbHLH93 and MdBT2.
Teosinte branched1/cycloidea/proliferating (TCP) transcription factors play a broad role in plant growth and development, but their involvement in the regulation of anthocyanin biosynthesis is currently unclear. In this study, anthocyanin biosynthesis induced by different light intensities in apple (Malus domestica) was found to be largely dependent on the functions of the MdMYB1 and MdTCP46 transcription factors. The expression of MdTCP46 was responsive to high light intensity, and under these conditions it promoted anthocyanin biosynthesis by direct interactions with MdMYB1 that enhanced the binding of the latter to its target genes. MdTCP46 also interacted with a bric-a-brac/tramtrack/broad (BTB) protein, MdBT2, that is responsive to high light intensity, which ubiquitinated MdTCP46 and mediated its degradation via the 26S proteasome pathway. Our results demonstrate that the dynamic regulatory module MdBT2-MdTCP46-MdMYB1 plays a key role in modulating anthocyanin biosynthesis at different light intensities in apple, and provides new insights into the post-transcriptional regulation of TCP proteins.
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