Alternative splicing of MaMYB16L regulates starch degradation in banana fruit during ripening

Abstract

The alternative splicing of select genes is an important mechanism to regulate responses to endogenous and environmental signals in plants. However, the role of alternative splicing in regulating fruit ripening remains unclear. Here, we discovered that MaMYB16L, an R1‐type MYB transcription factor, undergoes alternative splicing and generates two transcripts, the full‐length isoform MaMYB16L and a truncated form MaMYB16S, in banana fruit. During banana fruit ripening, the alternative splicing process intensifies with downregulated MaMYB16L and upregulated MaMYB16S. Moreover, MaMYB16L is a transcriptional repressor that directly binds with the promoters of many genes associated with starch degradation and MaDREB2, a positive ripening regulator, and represses their expression. In contrast, MaMBY16S lacks a DNA‐binding domain but competitively combines and forms non‐functional heterodimers with functional MaMYB16L. MaMYB16L‐MaMYB16S heterodimers decrease the binding capacity and transrepression activity of MaMYB16L. The downregulation of MaMYB16L and the upregulation of MaMYB16S, that is, a decreased ratio of active to non‐active isoforms, facilitates the activation of ripening‐related genes and thereby promotes fruit ripening. Furthermore, the transient overexpression of MaMYB16S promotes banana fruit ripening, whereas the overexpression of MaMYB16L delays this process. Therefore, the alternative splicing of MaMYB16L might generate a self‐controlled regulatory loop to regulate banana fruit ripening.

Alternative splicing during fruit development among fleshy fruits

“…AS has been proven to play important roles in a variety of plant processes, including fruit ripening [ 11 – 15 ]. In maize ( Zea mays L.), researchers have found that missplicing of U12-type introns in rgh3 can cause aberrant endosperm cell differentiation and proliferation [ 16 ].…”

Quantitative Transcriptomic and Proteomic Analysis of Fruit Development and Ripening in Watermelon (Citrullus lanatus)

“…Indeed, we found that at least 6,266 genes underwent AS during watermelon fruit ripening (data not shown). Most recently, MaMYB16L was reported to regulate starch degradation by alternative splicing in banana fruit during ripening ( Jiang et al, 2021 ). These results support the potential post-transcriptional and post-translational mechanisms in regulation of fruit ripening, which have also been described in other fruits, such as tomato, sweet orange and citrus ( Osorio et al, 2011 ; Pan et al, 2012 ; Wu et al, 2014b ; Belouah et al, 2019 ).…”

A Wheat TaTOE1-B1 Transcript TaTOE1-B1-3 Can Delay the Flowering Time of Transgenic Arabidopsis

“…The expression characteristics of different transcripts produced by the same gene, the functional positions of proteins coding by these transcripts, and the biological functions of these proteins may be different [ 37 , 38 ]. Previous studies have shown that MaMYB16 produces two transcripts, MaMYB16L and MaMYB16S , with opposite functions in controlling fruit ripening through alternative splicing [ 39 ]. MaMYB16L is a transcription inhibitor that inhibits fruit ripening by directly downregulating the expression of MaDREB2 ; MaMYB16S loses the ability to bind to DNA, but can bind to MaMYB16L competitively, and then form inactive dimers that ultimately promote fruit ripeness.…”