A banana R2R3‐MYB transcription factor MaMYB3 is involved in fruit ripening through modulation of starch degradation by repressing starch degradation‐related genes and MabHLH6

Abstract

Starch degradation is a necessary process determining banana fruit quality during ripening. Many starch degradation-related genes are well studied. However, the transcriptional regulation of starch degradation during banana fruit ripening remains poorly understood. In this study, we identified a MYB transcription factor (TF) termed MaMYB3, as a putative protein binding the promoter of MaGWD1, a member of glucan water dikinase (GWD) family which has been demonstrated as an important enzyme of starch degradation.MaMYB3 was ripening-and ethylene-repressible, and its expression was negatively correlated with starch degradation. Acting as a nucleus-localized transcriptional repressor, MaMYB3 repressed the transcription of 10 starch degradation-related genes, including MaGWD1, MaSEX4, MaBAM7-MaBAM8, MaAMY2B, MaAMY3, MaAMY3A, MaAMY3C, MaMEX1, and MapGlcT2-1, by directly binding to their promoters. Interestingly, a previously identified activator of starch degradation-related genes, MabHLH6, was also suppressed by MaMYB3. The ectopic overexpression of MaMYB3 in tomato down-regulated the expression of starch degradation-related genes, inhibited starch degradation and delayed fruit ripening. Based on these findings, we conclude that MaMYB3 negatively impacts starch degradation by directly repressing starch degradation-related genes and MabHLH6, and thereby delays banana fruit ripening. Collectively, our study expands our understanding of the complex transcriptional regulatory hierarchy modulating starch degradation during fruit ripening.

Genome-Wide Identification and Comparative Analysis of MYB Transcription Factor Family in Musa acuminata and Musa balbisiana

“…the ripening of banana fruit by obstructing starch degradation [55]. A progressive downregulation of MYB6 transcripts correlates with a conserved repressive role of this gene.…”

“…The expression of MaMYB6 decreased from day 0 to 7 (Figure 6a). The MYB6 is a transcriptional repressor that negatively regulates the ripening of banana fruit by obstructing starch degradation [55]. A progressive downregulation of MYB6 transcripts correlates with a conserved repressive role of this gene.…”

Transcriptome profiling of ‘Kyoho’ grape at different stages of berry development following 5-azaC treatment

“…Fruit softening involves the dissolution of the cell wall due to polymer depolymerization [34]. The degradation of cell wall starch was shown to be the main cause of banana fruit softening/ripening [35,36]. 'Kyoho' grape berry has a very hard texture at the very early stage of development, reaching peak hardness at 45 dpa before softening, which reflects the breakdown of the cell wall [32].…”

“…Two treatments were administered. Grape berries of uniform size and without mechanical damages were collected at five developmental stages-i.e., 25,35,45,55, and 65 dpa. The berries were labeled as shown in Table 3 in order to facilitate subsequent analysis.…”

MYB Transcription Repressors Regulate Plant Secondary Metabolism

“…Overexpression of TaMYB1D in tobacco (Nicotiana tabacum) resulted in the accumulation of lignin in stems and the enhanced expression of ROS-and stress-related genes in response to drought stress, however, the flavonoid content in leaves decreased (Wei et al, 2017). Ectopic expression of banana (Musa acuminata) MYB repressor MaMYB3 in tomato decreased degradation of starch and delayed fruit ripening by inhibiting starch metabolism genes and a positive regulator of starch degradation MabHLH6 (Fan et al, 2018).…”