Banana (Musa acuminata, AAA group) is a representative climacteric fruit with essential nutrients and pleasant flavors. Control of its ripening determines both the fruit quality and the shelf life. NAC (NAM, ATAF, CUC2) proteins, as one of the largest superfamilies of transcription factors, play crucial roles in various functions, especially developmental processes. Thus, it is important to conduct a comprehensive identification and characterization of the NAC transcription factor family at the genomic level in M. acuminata. In this article, a total of 181 banana NAC genes were identified. Phylogenetic analysis indicated that NAC genes in M. acuminata, Arabidopsis, and rice were clustered into 18 groups (S1–S18), and MCScanX analysis disclosed that the evolution of MaNAC genes was promoted by segmental duplication events. Expression patterns of NAC genes during banana fruit ripening induced by ethylene were investigated using RNA-Seq data, and 10 MaNAC genes were identified as related to fruit ripening. A subcellular localization assay of selected MaNACs revealed that they were all localized to the nucleus. These results lay a good foundation for the investigation of NAC genes in banana toward the biological functions and evolution.

Fruit ripening is the last phase of fruit growth and development. The initiation and progression of fruit ripening are highly modulated by a plethora of key genes, such as transcription factor (TF) genes. The WRKY gene family is a large group of TFs that play important roles in various cellular processes; nevertheless, the role of WRKY TF on fruit ripening remains enigmatic. Here, we report that a banana WRKY TF, MaWRKY49 functions in ethylene-induced fruit ripening by modulating the expression of fruit softening-related genes. We found that the expression of MaWRKY49 is highly induced by ethephon and inhibited by 1-methylcyclopropene, which is synchronous with the ripening process. Moreover, based on transcriptome data on fruit ripening, two pectate lyase (PL) genes that are involved in fruit softening were determined, and their expression pattern is also consistent with the fruit ripening process. Yeast one-hybrid and dual-luciferase assay confirmed that MaWRKY49 activated the transcription of two PL genes. In addition, transient overexpression of MaWRKY49 in banana fruits can apparently accelerate fruit ripening processs. Taken together, our findings indicate that MaWRKY49 acts as a potential modulator of fruit ripening by direct regulation of PL expression. This work contributes to developing the technology for improving the shelf-life of banana fruit.

Background: Banana plant height is an important trait for horticultural practices and semi-dwarf cultivars show better resistance to damages by wind and rain. However, the molecular mechanisms controlling the pseudostem height remain poorly understood. Herein, we studied the molecular changes in the pseudostem of a semi-dwarf banana mutant Aifen No. 1 (Musa spp. Pisang Awak sub-group ABB) as compared to its wild-type dwarf cultivar using a combined transcriptome and metabolome approach. Results: A total of 127 differentially expressed genes and 48 differentially accumulated metabolites were detected between the mutant and its wild type. Metabolites belonging to amino acid and its derivatives, flavonoids, lignans, coumarins, organic acids, and phenolic acids were up-regulated in the mutant. The transcriptome analysis showed the differential regulation of genes related to the gibberellin pathway, auxin transport, cell elongation, and cell wall modification. Based on the regulation of gibberellin and associated pathway-related genes, we discussed the involvement of gibberellins in pseudostem elongation in the mutant banana. Genes and metabolites associated with cell wall were explored and their involvement in cell extension is discussed. Conclusions: The results suggest that gibberellins and associated pathways are possibly developing the observed semi-dwarf pseudostem phenotype together with cell elongation and cell wall modification. The findings increase the understanding of the mechanisms underlying banana stem height and provide new clues for further dissection of specific gene functions.

Banana cultivars with the AAB genome group comprise diverse subgroups, such as Plantain, Silk, Iholena, and Pisang Raja, among others, which play an important role in food security in many developing countries. Some of these cultivars are susceptible to Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), the most destructive pathogen threatening banana production worldwide, and some of them are still largely unknown. We evaluated the resistance of 37 banana genotypes, including Plantain, Silk, Iholena, Maia Maoli/Popoulu, Pisang Raja, Pome, and Mysore, to Foc TR4 under both greenhouse and field conditions. Genotypes from the Silk and Iholena subgroups were highly susceptible to Foc TR4. Pome and Mysore showed resistance and intermediate resistance, respectively. However, Pisang Raja ranged from susceptible to intermediate resistance. One cultivar from the Maia Maoli/Popoulu subgroup was highly susceptible, while the other displayed significant resistance. Most Plantain cultivars exhibited high resistance to Foc TR4, except two French types of cultivar, ‘Uganda Plantain’ and ‘Njombe N°2’, which were susceptible. The susceptibility to Foc TR4 of some of the AAB genotypes evaluated, especially Plantain and other cooking bananas, indicates that growers dependent on these varieties need to be included as part of the prevention and integrated Foc TR4 management strategies, as these genotypes play a crucial role in food security and livelihoods.

Trait tagging through molecular markers is an important molecular breeding tool for crop improvement. SSR markers encoded by functionally relevant parts of a genome are well suited for this task because they may be directly related to traits. However, a limited number of these markers are known for Musa spp. Here, we report 35136 novel functionally relevant SSR markers (FRSMs). Among these, 17,561, 15,373 and 16,286 FRSMs were mapped in-silico to the genomes of Musa acuminata, M. balbisiana and M. schizocarpa, respectively. A set of 273 markers was validated using eight accessions of Musa spp., from which 259 markers (95%) produced a PCR product of the expected size and 203 (74%) were polymorphic. In-silico comparative mapping of FRSMs onto Musa and related species indicated sequence-based orthology and synteny relationships among the chromosomes of Musa and other plant species. Fifteen FRSMs were used to estimate the phylogenetic relationships among 50 banana accessions, and the results revealed that all banana accessions group into two major clusters according to their genomic background. Here, we report the first large-scale development and characterization of functionally relevant Musa SSR markers. We demonstrate their utility for germplasm characterization, genetic diversity studies, and comparative mapping in Musa spp. and other monocot species. The sequences for these novel markers are freely available via a searchable web interface called Musa Marker Database.

Recently, many control methods have been tried and applied in the Fusarium wilt disease control of banana and have achieved definite progresses. In this study, by using ‘Zhongjiao No.3’ and ‘Zhongjiao No.4’ banana seedlings as materials, the effects of Serendipita indica and bamboo fungus (Dictyophorae echinovolvata) culture substrates on the growth and Fusarium wilt disease resistance of banana were investigated. Results showed that the plant height, leaf length, leaf width, root length and root thickness, aboveground part fresh weight, root fresh weight, and relative chlorophyll content and nitrogen content in leaves of banana seedlings colonized with S. indica were all greater than those of non-colonized controls, while these parameters of banana seedlings grown in nutrient soil containing D. echinovolvata culture substrates were significantly suppressed. Both S. indica non-colonized and colonized seedlings cultivated in nutrient containing 1/4 D. echinovolvata culture substrates showed much milder symptoms compared with those cultivated in normal nutrient soil, indicating that the addition of bamboo fungus substrates to the soil can enhance the Fusarium wilt resistance of banana. The results obtained in this study can provide a basis for the application of S. indica and bamboo fungus in the prevention and control of banana Fusarium wilt disease.