Journal
PLANT PHYSIOLOGY
Volume 186, Issue 1, Pages 549-568Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/plphys/kiab098
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Funding
- National Natural Science Foundation of China [32001993, 31972362]
- Project of the Shandong Natural Science Foundation [ZR2020QC143]
- Breeding Plan of the Shandong Provincial Qingchuang Research Team [2019]
- High-Level Scientific Research Foundation of Qingdao Agricultural University [663/1119045]
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This study revealed that MdMYB44 transcription factor negatively regulates fruit malate accumulation by repressing the promoter activity of malate-associated genes. Two single-nucleotide polymorphisms in the MdMYB44 promoter were shown to affect fruit malate content, providing a valuable tool for the selection of fruit acidity in apple breeding. The research is crucial for understanding the complex molecular mechanisms of fruit malate accumulation and for accelerating germplasm innovation in apple species and cultivars.
Deciphering the mechanism of malate accumulation in apple (Malus domestica Borkh.) fruits can help to improve their flavor quality and enhance their benefits for human health. Here, we analyzed malate content as a quantitative trait that is determined mainly by genetic effects. In a previous study, we identified an R2R3-MYB transcription factor named MdMYB44 that was a candidate gene in qtl08.1 (quantitative trait locus mapped to chromosome 8) of fruit malate content. In the present study, we established that MdMYB44 negatively regulates fruit malate accumulation by repressing the promoter activity of the malate-associated genes Ma1 (Al-Activated Malate Transporter 9), Ma10 (P-type ATPase 10), MdVHA-A3 (V-type ATPase A3), and MdVHA-D2 (V-type ATPase D2). Two single-nucleotide polymorphisms (SNPs) in the MdMYB44 promoter, SNP A/G and SNP T/-, were experimentally shown to associate with fruit malate content. The TATA-box in the MdMYB44 promoter in the presence of SNP A enhances the basal activity of the MdMYB44 promoter. The binding of a basic-helix-loop-helix transcription factor MdbHLH49 to the MdMYB44 promoter was enhanced by the presence of SNP T, leading to increased MdMYB44 transcript levels and reduced malate accumulation. Furthermore, MdbHLH49 interacts with MdMYB44 and enhances MdMYB44 activity. The two SNPs could be used in combination to select for sour or non-sour apples, providing a valuable tool for the selection of fruit acidity by the apple breeding industry. This research is important for understanding the complex molecular mechanisms of fruit malate accumulation and accelerating the development of germplasm innovation in apple species and cultivars.
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