Abstract
Fruit ripening is regulated by epigenetic modifications and transcription factors, which may function independently or as protein complexes. Our previous study showed that the apple histone deacetylase19 (MdHDA19) suppresses fruit ripening through the deacetylation of histones in related genes. Here, a MADS-box transcription factor (MdMADS6) was identified using a yeast two-hybrid (Y2H) assay as a candidate protein that interacts with MdHDA19 during apple fruit ripening. Furthermore, Y2H, bimolecular fluorescence complementation (BiFC) and pull-down assays were used to confirm the interaction between MdHDA19 and MdMADS6. Agrobacterium-mediated transient transformation and yeast one-hybrid assays showed that MdMADS6 promoted carotenoid accumulation in apple fruit by acting on the downstream target genes related to carotenoid biosynthesis. In summary, we conclude that, in the early stages of fruit development, the expression of MdMADS6 was maintained at lower levels, where it interacted with MdHDA19 to form a protein complex that inhibited the expression of the downstream genes. At the late stages of fruit development, active expression of MdMADS6 dissociated the protein complex of MdMADS6 and MdHDA19 and consequently promoted the expression of carotenoid biosynthesis genes as well as carotenoid accumulation.
Highlights
Numerous physiological and biochemical processes occur during apple fruit ripening and affect its quality, post-harvest life and value [1]
We demonstrate that MdMADS6 and MdHDA19 may form a protein complex to regulate the ripening of apple fruits
The results showed that the expression levels of MdCCD1 and MdPDS were lower at the early than at the late stage of fruit development, especially the expression level of MdCCD1 was significantly increased at the later stage (Figure 4B)
Summary
Numerous physiological and biochemical processes occur during apple fruit ripening and affect its quality, post-harvest life and value [1]. Fruits undergo changes in texture, color and aroma during the ripening process. Previous studies revealed that epigenetic modifications, such as DNA methylation, histone acetylation, phosphorylation and ubiquitination, constitute a major factor in regulating fruit ripening [2]. Histone modification is a dynamic process where acetylation is catalyzed by histone acetyltransferases (HATs) and is related to transcriptional activation, whereas deacetylation is catalyzed by histone deacetylases (HDACs) and is involved in transcriptional inhibition [3]. Many studies have showed that histone deacetylation plays an important role in regulating fruit ripening. The expression of genes involved in carotenoid and ethylene biosynthesis has been reported to decrease after silencing histone deacetylases
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