Transcriptomics and Gene Family Identification of Cell Wall-Related Differentially Expressed Genes Reveal MaXTH32.5 Involved in Fruit Firmness During Banana Ripening

Banana (<i>Musa</i> spp.) is a typical climacteric fruit. <i>Xyloglucan endotransglucosylase/hydrolase</i> (<i>XTH</i>) is a key factor regulating plant cell wall dynamic remodeling and participates in fruit ripening. To clarify the core physiological traits of banana ripening, four ripening stages of banana cultivar (<i>Musa</i> AAA 'Minai No. 1') fruits in the fully green stage (S1), green-yellow stage (S2), fully yellow stage (S3), and yellow with brown spots stage (S4) were used in this study's experimental materials, to examine dynamic changes in key physiological-biochemical properties. The results showed that fruit firmness decreased continuously, starch content first increased then decreased, and soluble protein and total soluble solids (TSS) accumulated gradually during the ripening stages of banana fruits. Transcriptome analysis of the four stages found that there were 14,315 differentially expressed genes (DEGs) in S1 versus S4, the GO enrichment pathway is enriched in "protein dephosphorylation", and the KEGG enrichment pathway is enriched in the "Protein processing in endoplasmic reticulum" and "Ubiquitin mediated proteolysis" pathways. The fruit ripening process involves the processing of numerous proteins. The heatmap revealed that <i>MaXTH32.5</i> was significantly up-regulated during banana ripening and the result of RT-qPCR is consistent with the transcriptome data. A total of 989 <i>XTH</i> members across 16 <i>Musa</i> varieties of the XTH gene family were further identified. Among them, MaXTH32.5 localized at the chloroplast, and transient overexpression of <i>MaXTH32.5</i> significantly reduced banana fruit firmness and may be involved in regulating ripening in banana fruits. This study indicated that the differential expression of XTH gene family members may regulate ripening-related processes in banana and <i>MaXTH32.5</i> as a key candidate, providing insights into banana ripening mechanisms and a foundation for subsequent <i>Musa XTH</i> research.