Efficient regeneration and genetic transformation platform applicable to five Musa varieties

Background: Banana (Musa spp.) is an important staple food, economic crop, and nutritional fruit worldwide. Conventional breeding has been seriously hampered by their long generation time, polyploidy, and sterility of most cultivated varieties. Establishment of an efficient regeneration and transformation system for banana is critical to its genetic improvement and functional genomics. Results: In this study, a vigorous and repeatable transformation system for banana using direct organogenesis was developed. The greatest number of shoots per explant for all five Musa varieties was obtained using Murashige and Skoog medium supplemented with 8.9 µM benzylaminopurine and 9.1 µM thidiazuron. One immature male flower could regenerate 380­456, 310­372, 200­240, 130­156, and 100­130 well-developed shoots in only 240­270 d for Gongjiao, Red banana, Rose banana, Baxi, and Xinglongnaijiao, respectively. Longitudinal sections of buds were transformed through particle bombardment combined with Agrobacterium-mediated transformation using a promoterless ß-glucuronidase (GUS) reporter gene; the highest transformation efficiency was 9.81% in regenerated Gongjiao plantlets in an optimized selection medium. Transgenic plants were confirmed by a histochemical assay of GUS, polymerase chain reaction, and Southern blot. Conclusions: Our robust transformation platform successfully generated hundreds of transgenic plants. Such a platform will facilitate molecular breeding and functional genomics of banana.

Molecular cloning and expression analysis of the MaASR1 gene in banana and functional characterization under salt stress

Background Abscisic acid (ABA)-, stress- and ripening-induced protein (ASR) is plant-specific hydrophilic transcriptional regulators involved in sucrose stress and wounding in banana. However, it is not known whether banana ASR genes confer salt stress tolerance. The contexts of the study was to analysis the sequence characterization of banana ASR1, and identify its expression patterns and function under salt stress using quantitative real-time PCR (qPCR) and overexpression in Arabidopsis. The purpose was to evaluate the role of banana ASR1 to salt stress tolerance employed by plants. Results A full-length cDNA isolated from banana fruit was named MaASR1, and it had a 432 bp open reading frame (ORF) encoding 143 amino acids. MaASR1 was preferential expression in roots and leaves compared to low expression in fruits, rhizomes and flowers. Under salt stress, the expression of MaASR1 quickly increased and highest expression level was detected in roots and leaves at 4 h, and then gradually decreased. These results suggested that MaASR1 expression was induced under salt stress. MaASR1 protein was localized in the nucleus and plasma membrane. MaASR1 was transformed to Arabidopsis and verified by southern and northern analysis, transgenic lines L14 and L38 integrated one and two copies of MaASR1, respectively, while overexpression in transgenic lines provided evidence for the role of MaASR1 to salt stress tolerance. Conclusions This study demonstrated that overexpression of MaASR1 in Arabidopsis confers salt stress tolerance by reducing the expression of ABA/stress-responsive genes, but does not affect the expression of the ABA-independent pathway and biosynthesis pathway genes.