Yulin Hu

Identification and evaluation of two diagnostic markers linked to Fusarium wilt resistance (race 4) in banana (Musa spp.).

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cubense race 4 (FOC4) results in vascular tissue damage and ultimately death of banana (Musa spp.) plants. Somaclonal variants of in vitro micropropagated banana can hamper success in propagation of genotypes resistant to FOC4. Early identification of FOC4 resistance in micropropagated banana plantlets is difficult, however. In this study, we identified sequence-characterized amplified region (SCAR) markers of banana associated with resistance to FOC4. Using pooled DNA from resistant or susceptible genotypes and 500 arbitrary 10-mer oligonucleotide primers, 24 random amplified polymorphic DNA (RAPD) products were identified. Two of these RAPD markers were successfully converted to SCAR markers, called ScaU1001 (GenBank accession number HQ613949) and ScaS0901 (GenBank accession number HQ613950). ScaS0901 and ScaU1001 could be amplified in FOC4-resistant banana genotypes (“Williams 8818-1” and Goldfinger), but not in five tested banana cultivars susceptible to FOC4. The two SCAR markers were then used to identify a somaclonal variant of the genotype “Williams 8818-1”, which lost resistance to FOC4. Hence, the identified SCAR markers can be applied for a rapid quality control of FOC4-resistant banana plantlets immediately after the in vitro micropropagation stage. Furthermore, ScaU1001 and ScaS0901 will facilitate marker-assisted selection of new banana cultivars resistant to FOC4.

Metabolism of Flavonoids in Novel Banana Germplasm during Fruit Development

Banana is a commercially important fruit, but its flavonoid composition and characteristics has not been well studied in detail. In the present study, the metabolism of flavonoids was investigated in banana pulp during the entire developmental period of fruit. ‘Xiangfen 1,’ a novel flavonoid-rich banana germplasm, was studied with ‘Brazil’ serving as a control. In both varieties, flavonoids were found to exist mainly in free soluble form and quercetin was the predominant flavonoid. The most abundant free soluble flavonoid was cyanidin-3-O-glucoside chloride, and quercetin was the major conjugated soluble and bound flavonoid. Higher content of soluble flavonoids was associated with stronger antioxidant activity compared with the bound flavonoids. Strong correlation was observed between antioxidant activity and cyanidin-3-O-glucoside chloride content, suggesting that cyanidin-3-O-glucoside chloride is one of the major antioxidants in banana. In addition, compared with ‘Brazil,’ ‘Xiangfen 1’ fruit exhibited higher antioxidant activity and had more total flavonoids. These results indicate that soluble flavonoids play a key role in the antioxidant activity of banana, and ‘Xiangfen 1’ banana can be a rich source of natural antioxidants in human diets.

Genome-wide identification and expression profiling reveal tissue-specific expression and differentially-regulated genes involved in gibberellin metabolism between Williams banana and its dwarf mutant

BackgroundDwarfism is one of the most valuable traits in banana breeding because semi-dwarf cultivars show good resistance to damage by wind and rain. Moreover, these cultivars present advantages of convenient cultivation, management, and so on. We obtained a dwarf mutant ‘8818-1’ through EMS (ethyl methane sulphonate) mutagenesis of Williams banana 8818 (Musa spp. AAA group). Our research have shown that gibberellins (GAs) content in 8818-1 false stems was significantly lower than that in its parent 8818 and the dwarf type of 8818-1 could be restored by application of exogenous GA3. Although GA exerts important impacts on the 8818-1 dwarf type, our understanding of the regulation of GA metabolism during banana dwarf mutant development remains limited.ResultsGenome-wide screening revealed 36 candidate GA metabolism genes were systematically identified for the first time; these genes included 3 MaCPS, 2 MaKS, 1 MaKO, 2 MaKAO, 10 MaGA20ox, 4 MaGA3ox, and 14 MaGA2ox genes. Phylogenetic tree and conserved protein domain analyses showed sequence conservation and divergence. GA metabolism genes exhibited tissue-specific expression patterns. Early GA biosynthesis genes were constitutively expressed but presented differential regulation in different tissues in Williams banana. GA oxidase family genes were mainly transcribed in young fruits, thus suggesting that young fruits were the most active tissue involved in GA metabolism, followed by leaves, bracts, and finally approximately mature fruits. Expression patterns between 8818 and 8818-1 revealed that MaGA20ox4, MaGA20ox5, and MaGA20ox7 of the MaGA20ox gene family and MaGA2ox7, MaGA2ox12, and MaGA2ox14 of the MaGA2ox gene family exhibited significant differential expression and high-expression levels in false stems. These genes are likely to be responsible for the regulation of GAs content in 8818-1 false stems.ConclusionOverall, phylogenetic evolution, tissue specificity and differential expression analyses of GA metabolism genes can provide a better understanding of GA-regulated development in banana. The present results revealed that MaGA20ox4, MaGA20ox5, MaGA20ox7, MaGA2ox7, MaGA2ox12, and MaGA2ox14 were the main genes regulating GA content difference between 8818 and 8818-1. All of these genes may perform important functions in the developmental processes of banana, but each gene may perform different functions in different tissues or during different developmental stages.