Banana (Musa spp.) is susceptible to low-temperature stress and other environmental stresses, which can hinder the growth and development. Succinic semialdehyde dehydrogenase (SSADH) is critical for GABA biosynthesis and plays a crucial role in plants. However, the SSADH genes of bananas have not been studied. This study found 19 MaSSADHs, 18 MbSSADHs, and 18 MiSSADHs from the banana genome. According to the phylogenetic tree, these genes can be categorized into five branches. This study cloned the MaSSADH1-14 from banana. The subcellular localization assays of MaSSADH1-14 in tobacco leaves confirmed that the presence of SSADH was not only localized mitochondrion but also localized chloroplast. The cis-elements of the SSADH gene family are related to the potential regulation of the banana SSADH gene family; their involvement in diverse stress responses. Transcriptomic data was utilized to examine the effect of MaSSADH genes under cold stress in bananas. The results of RT-qPCR were consistent with transcriptome data. These results showed that most MaSSADHs are passively responsive to low-temperature treatment. In addition, transient overexpression of MaSSADH1-14 in Nicotiana benthamiana leaves resulted in the content of GABA increasing, indicating that MaSSADH1-14 may be involved in the accumulation of GABA of banana. Collectively, these results improve knowledge of the SSADH gene family in banana and establish a basis for comprehending its biological roles in response to low temperatures.

Banana (Musa spp.) is a typical climacteric fruit. Xyloglucan endotransglucosylase/hydrolase (XTH) 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 (Musa 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 MaXTH32.5 was significantly up-regulated during banana ripening and the result of RT-qPCR is consistent with the transcriptome data. A total of 989 XTH members across 16 Musa varieties of the XTH gene family were further identified. Among them, MaXTH32.5 localized at the chloroplast, and transient overexpression of MaXTH32.5 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 MaXTH32.5 as a key candidate, providing insights into banana ripening mechanisms and a foundation for subsequent Musa XTH research.

Banana productivity is severely limited by drought, yet the molecular basis of drought adaptation and endophyte-mediated stress alleviation remains poorly understood. Here, we performed a genome-wide analysis of the SQUAMOSA promoter-binding protein-like (SPL) transcription factor family in Musa acuminata and examined their transcriptional responses to drought stress and Serendipita indica inoculation. We identified 38 MaSPL genes, all encoding proteins with the conserved SBP domain and predicted nuclear localization. Phylogenetic, motif, gene structure, and collinearity analyses indicated that MaSPL genes are evolutionarily conserved, unevenly distributed across chromosomes, and expanded primarily through segmental duplication under purifying selection. Promoter analysis showed several cis-acting elements and transcription factor binding sites related to light, phytohormone, and stress signaling. Ten MaSPL genes were predicted as putative targets of miR156. qRT-PCR analysis showed that drought stress markedly downregulated the tested MaSPL genes, whereas miR156a expression increased, supporting an inverse regulatory relationship. Under drought, S. indica inoculation enhanced expression of most tested MaSPLs, restoring transcript accumulation while reducing miR156a to near-basal levels. Notable responses were observed in members of the MaSPL2, MaSPL9, and MaSPL13, respectively. S. indica improves drought tolerance by enhancing antioxidant defenses, reducing oxidative stress, and preserving photosynthetic and osmotic stability. Taken together, our results demonstrate that S. indica confers drought resilience in banana by counteracting drought-induced repression of MaSPL genes via the miR156–SPL module and by strengthening key physiological defense mechanisms.