Transcriptome analysis provides insight into the regulatory mechanisms underlying pollen germination recovery at normal high ambient temperature in wild banana (Musa itinerans)

Introduction

Cultivated banana are polyploid, with low pollen fertility, and most cultivars are male sterile, which leads to difficulties in banana breeding research. The selection of male parent with excellent resistance and pollen fertility is therefore essential for banana breeding. Wild banana (Musa itinerans) have developed many good characteristics during natural selection and constitute an excellent gene pool for breeding. Therefore, research on wild banana breeding is very important for banana breeding.

Results

In the current analysis, we examined the changes in viability of wild banana pollens at different temperatures by in vitro germination, and found that the germination ability of wild banana pollens cultured at 28°C for 2 days was higher than that of pollens cultured at 23°C (pollens that could not germinate normally under low temperature stress), 24°C (cultured at a constant temperature for 2 days) and 32°C (cultured at a constant temperature for 2 days). To elucidate the molecular mechanisms underlying the germination restoration process in wild banana pollens, we selected the wild banana pollens that had lost its germination ability under low temperature stress (23°C) as the control group (CK) and the wild banana pollens that had recovered its germination ability under constant temperature incubation of 28°C for 2 days as the treatment group (T) for transcriptome sequencing. A total of 921 differentially expressed genes (DEGs) were detected in CK vs T, of which 265 were up-regulated and 656 were down-regulated. The combined analysis of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed that the activation, metabolism of various substances (lipids, sugars, amino acids) play a major role in restoring pollen germination capacity. TCA cycle and the sesquiterpenoid and triterpenoid biosynthetic pathways were also significantly enriched in the KEGG pathway. And we found that some DEGs may be associated with pollen wall formation, DNA methylation and DNA repair. The cysteine content, free fatty acid (FFA) content, H2O2 content, fructose content, and sucrose content of pollen were increased at treatment of 28°C, while D-Golactose content was decreased. Finally, the GO pathway was enriched for a total of 24 DEGs related to pollen germination, of which 16 DEGs received targeted regulation by 14 MYBs.

Discussions

Our study suggests that the balance between various metabolic processes, pollen wall remodelling, DNA methylation, DNA repairs and regulation of MYBs are essential for germination of wild banana pollens.

A Perspective Review on Understanding Drought Stress Tolerance in Wild Banana Genetic Resources of Northeast India

The enormous perennial monocotyledonous herb banana (Musa spp.), which includes dessert and cooking varieties, is found in more than 120 countries and is a member of the order Zingiberales and family Musaceae. The production of bananas requires a certain amount of precipitation throughout the year, and its scarcity reduces productivity in rain-fed banana-growing areas due to drought stress. To increase the tolerance of banana crops to drought stress, it is necessary to explore crop wild relatives (CWRs) of banana. Although molecular genetic pathways involved in drought stress tolerance of cultivated banana have been uncovered and understood with the introduction of high-throughput DNA sequencing technology, next-generation sequencing (NGS) techniques, and numerous "omics" tools, unfortunately, such approaches have not been thoroughly implemented to utilize the huge potential of wild genetic resources of banana. In India, the northeastern region has been reported to have the highest diversity and distribution of Musaceae, with more than 30 taxa, 19 of which are unique to the area, accounting for around 81% of all wild species. As a result, the area is regarded as one of the main locations of origin for the Musaceae family. The understanding of the response of the banana genotypes of northeastern India belonging to different genome groups to water deficit stress at the molecular level will be useful for developing and improving drought tolerance in commercial banana cultivars not only in India but also worldwide. Hence, in the present review, we discuss the studies conducted to observe the effect of drought stress on different banana species. Moreover, the article highlights the tools and techniques that have been used or that can be used for exploring and understanding the molecular basis of differentially regulated genes and their networks in different drought stress-tolerant banana genotypes of northeast India, especially wild types, for unraveling their potential novel traits and genes.

Resistance of Musa balbisiana accessions of the Philippines to banana bunchy top virus

Banana bunchy top disease (BBTD) is caused by banana bunchy top virus (BBTV), the most important virus affecting banana. Currently, no cultivar or accession of banana has complete resistance to BBTD. A total of 36 wild Musa spp. accessions, including 34 Musa balbisiana and two M. acuminata subsp. errans ('Agutay'), were screened for resistance against BBTV. In greenhouse tests using viruliferous banana aphids (Pentalonia nigronervosa), all M. balbisiana accessions remained symptomless and BBTV was not detected in any of these plants by PCR at three and six months post inoculation. In contrast, 100% disease incidence was recorded in M. acuminata subsp. errans and in cv. Lakatan susceptible control plants. The PCR-negative M. balbisiana plants were then transferred to a field with high BBTV inoculum pressure where they remained symptomless and PCR-negative for up to five years, while all cv. Lakatan developed BBTD. Wild M. balbisiana accessions showed a high level of resistance, possibly immunity, to BBTV and are expected to provide a resource for conventional and marker assisted breeding.

Cheesman) plant

Ensete superbum Roxb. Cheesman (wild banana) is used as therapeutic edible by various ethnic groups around the world. The antioxidant potential of ethanolic, methanolic, and aqueous extracts of E. superbum ripe peel, seed, flower, and bract was tested using in vitro and ex vivo models, and their polyphenolic constituents were determined by RP-HPLC and LC/MS-ESI-TOF. E. superbum extracts were rich in anthocyanins, flavonols, flavone, biflavonoid, and phenolic acid derivatives. The Partial Least Square Regression analysis highlighted the contribution of individual phenolics toward the antioxidant activity. Bract aqueous extract demonstrated best antioxidant activity in DPPH radical scavenging activity assay (IC₅₀ of 21.97 μg/ml), Oxygen Radical Absorbance Capacity assay (207.97 µM TE/g) with highest Antioxidant Activity Index (1.79), and showed the highest cellular antioxidant activity (67.02 µM quercetin equivalents/g) in Caco2 cells. These findings highlight the potential of E. superbum as valuable source of natural antioxidants, which can be used as pharmaceutical and functional food ingredient. PRACTICAL APPLICATIONS: Wild banana has been used as a medicinal plant for ages throughout the world. However, the systematic analysis of its constituents and their beneficial effect is lacking. Our approach to search the effective plant part showed that the bioactive ingredients are concentrated in aqueous extracts of bracts. This study provides a basis for the antioxidant mechanisms of various wild banana plant parts, and will promote the utilization of an under-utilized wild edible plant.

The complete chloroplast genome sequence of wild banana, Musa balbisiana variety 'Pisang Klutuk Wulung' (Musaceae)

Musa balbisiana is a wild-type species of banana, endemic to Southern China, Eastern South Asia, and Northern Southeast Asia. The M. balbisiana variety 'Pisang Klutuk Wulung' is one of the possible ancestral parents of modern cultivated bananas, but its wild populations are now in decline. In this study, we report the complete chloroplast genome sequence of wild banana, M. balbisiana diploid variety 'Pisang Klutuk Wulung'. The M. balbisiana chloroplast genome is found to be 169,458 bp in length and has a base composition of A (31.44%), G (18.16%), C (18.61%), and T (31.79%). The genome contained two short inverted repeat (IRa and IRb) regions (35,084 bp), which were separated by a large single copy (LSC) region (87,805 bp) and a small single copy (SSC) region (11,485 bp). The genome encodes 113 unique genes, including 79 protein-coding genes, 30 transfer RNA (tRNA) genes, and four ribosomal RNA (rRNA) genes. Further, phylogenetic analysis suggested that M. balbisiana is closely related to the species of M. textilis. This complete chloroplast genome will provide valuable information for the development of DNA markers for future population and conservation studies of M. balbisiana.

"A draft Musa balbisiana genome sequence for molecular genetics in polyploid, inter- and intra-specific Musa hybrids"

BACKGROUND

Modern banana cultivars are primarily interspecific triploid hybrids of two species, Musa acuminata and Musa balbisiana, which respectively contribute the A- and B-genomes. The M. balbisiana genome has been associated with improved vigour and tolerance to biotic and abiotic stresses and is thus a target for Musa breeding programs. However, while a reference M. acuminata genome has recently been released (Nature 488:213-217, 2012), little sequence data is available for the corresponding B-genome.To address these problems we carried out Next Generation gDNA sequencing of the wild diploid M. balbisiana variety 'Pisang Klutuk Wulung' (PKW). Our strategy was to align PKW gDNA reads against the published A-genome and to extract the mapped consensus sequences for subsequent rounds of evaluation and gene annotation.

RESULTS

The resulting B-genome is 79% the size of the A-genome, and contains 36,638 predicted functional gene sequences which is nearly identical to the 36,542 of the A-genome. There is substantial sequence divergence from the A-genome at a frequency of 1 homozygous SNP per 23.1 bp, and a high degree of heterozygosity corresponding to one heterozygous SNP per 55.9 bp. Using expressed small RNA data, a similar number of microRNA sequences were predicted in both A- and B-genomes, but additional novel miRNAs were detected, including some that are unique to each genome. The usefulness of this B-genome sequence was evaluated by mapping RNA-seq data from a set of triploid AAA and AAB hybrids simultaneously to both genomes. Results for the plantains demonstrated the expected 2:1 distribution of reads across the A- and B-genomes, but for the AAA genomes, results show they contain regions of significant homology to the B-genome supporting proposals that there has been a history of interspecific recombination between homeologous A and B chromosomes in Musa hybrids.

CONCLUSIONS

We have generated and annotated a draft reference Musa B-genome and demonstrate that this can be used for molecular genetic mapping of gene transcripts and small RNA expression data from several allopolyploid banana cultivars. This draft therefore represents a valuable resource to support the study of metabolism in inter- and intraspecific triploid Musa hybrids and to help direct breeding programs.