Melatonin-induced physiology and transcriptome changes in banana seedlings under salt stress conditions.

Soil salinization poses a serious threat to the ecological environment and agricultural production and is one of the most common abiotic stresses in global agricultural production. As a salt-sensitive plant, the growth, development, and production of bananas (Musa acuminata L.) are restricted by salt stress. Melatonin is known to improve the resistance of plants to stress. The study analyzed the effects of 100 µM melatonin on physiological and transcriptome changes in banana varieties (AAA group cv. Cavendish) under 60 mmol/l of NaCl salt stress situation. The phenotypic results showed that the application of exogenous melatonin could maintain banana plants' health growth and alleviate the damage caused by salt stress. The physiological data show that the application of exogenous melatonin can enhance salt tolerance of banana seedlings by increasing the content of proline content and soluble protein, slowing down the degradation of chlorophyll, reducing membrane permeability and recovery of relative water content, increasing the accumulation of MDA, and enhancing antioxidant defense activity. Transcriptome sequencing showed that melatonin-induced salt tolerance of banana seedlings involved biological processes, molecular functions, and cellular components. We also found that differentially expressed genes (DEGs) are involved in a variety of metabolic pathways, including amino sugar and nucleotide sugar metabolism, phenylalanine metabolism, cyanoamino acid metabolism, starch and sucrose metabolism, and linoleic acid metabolism. These major metabolism and biosynthesis may be involved in the potential mechanism of melatonin under salt stress. Furthermore, some members of the transcription factor family, such as MYB, NAC, bHLH, and WRKY, might contribute to melatonin alleviating salt stress tolerance of the banana plant. The result laid a basis for further clarifying the salt stress resistance mechanism of bananas mediated by exogenous melatonin and provides theoretical bases to utilize melatonin to improve banana salt tolerance in the future.

Physiological Analysis and Transcriptome Sequencing Reveal the Effects of Salt Stress on Banana (Musa acuminata cv. BD) Leaf.

The salinization of soil is a widespread environmental problem. Banana (Musa acuminata L.) is a salt-sensitive plant whose growth, development, and production are constrained by salt stresses. However, the tolerance mechanism of this salt-sensitive banana to salt stress is still unclear. This study aimed to investigate the influence of NaCl treatment on phenotypic, physiological, and transcriptome changes in bananas. We found that the content of root activity, MDA, Pro, soluble sugar, soluble protein, and antioxidant enzymes activity in salt-stress treatment were significantly higher than the control in bananas. Transcriptome sequencing result identified an overall of 3,378 differentially expressed genes (DEGs) in banana leaves, and the Kyoto Encyclopedia of Genes and Genomes analysis indicated that these DEGs were involved in phenylpropanoid biosynthesis process, ribosome process, starch and sucrose metabolism, amino sugar process, and plant hormone signal transduction process that had simultaneously changed their expression under salt stress, which indicated these DEGs may play a role in promoting BD banana growth under salt treatments. The genes which were enriched in the phenylpropanoid biosynthesis process, starch and sucrose metabolism process, amino sugar process, and plant hormone signal transduction process were specifically regulated to respond to the salt stress treatments. Here, totally 48 differentially expressed transcription factors (TFs), including WRKY, MYB, NAC, and bHLH, were annotated in BD banana under salt stress. In the phenylpropane biosynthesis pathway, all transcripts encoding key enzymes were found to be significantly up-regulated, indicating that the genes in these pathways may play a significant function in the response of BD banana to salt stress. In conclusion, this study provides new insights into the mechanism of banana tolerance to salt stress, which provides a potential application for the genetic improvement of banana with salt tolerance.

The genome evolution and domestication of tropical fruit mango.

BACKGROUND: Mango is one of the world's most important tropical fruits. It belongs to the family Anacardiaceae, which includes several other economically important species, notably cashew, sumac and pistachio from other genera. Many species in this family produce family-specific urushiols and related phenols, which can induce contact dermatitis. RESULTS: We generate a chromosome-scale genome assembly of mango, providing a reference genome for the Anacardiaceae family. Our results indicate the occurrence of a recent whole-genome duplication (WGD) event in mango. Duplicated genes preferentially retained include photosynthetic, photorespiration, and lipid metabolic genes that may have provided adaptive advantages to sharp historical decreases in atmospheric carbon dioxide and global temperatures. A notable example of an extended gene family is the chalcone synthase (CHS) family of genes, and particular genes in this family show universally higher expression in peels than in flesh, likely for the biosynthesis of urushiols and related phenols. Genome resequencing reveals two distinct groups of mango varieties, with commercial varieties clustered with India germplasms and demonstrating allelic admixture, and indigenous varieties from Southeast Asia in the second group. Landraces indigenous in China formed distinct clades, and some showed admixture in genomes. CONCLUSIONS: Analysis of chromosome-scale mango genome sequences reveals photosynthesis and lipid metabolism are preferentially retained after a recent WGD event, and expansion of CHS genes is likely associated with urushiol biosynthesis in mango. Genome resequencing clarifies two groups of mango varieties, discovers allelic admixture in commercial varieties, and shows distinct genetic background of landraces.

Influence of irrigation during the growth stage on yield and quality in mango (Mangifera indica L).

Although being one of the few drought-tolerant plants, mango trees are irrigated to ensure optimum and consistent productivity in China. In order to better understand the effects of soil water content on mango yield and fruit quality at fruit growth stage, irrigation experiments were investigated and the object was to determine the soil water content criteria at which growth and quality of mango would be optimal based on soil water measured by RHD-JS water-saving irrigation system through micro-sprinkling irrigation. Five soil water content treatments (relative to the percentage of field water capacity) for irrigation (T1:79%-82%, T2:75%-78%, T3:71%-74%, T4: 65%-70%, T5:63%-66%) were compared in 2013. Amount of applied irrigation water for different treatments varied from 2.93m3 to 1.08 m3. The results showed that mango fruit production and quality at fruit growth stage were significantly affected under different irrigation water amounts. Variation in soil water content not only had effects on fruit size, but also on fruit yield. The highest fruit yield and irrigation water use efficiency were obtained from the T4 treatment. Irrigation water amount also affected fruit quality parameters like fruit total soluble solids, soluble sugar, starch, titratable acid and vitamin C content. Comprehensive evaluation of the effect of indexs of correlation on irrigation treatment by subordinate function showed that when the soil moisture content were controlled at about 65-70% of the field water moisture capacity, water demand in the growth and development of mango could be ensured, and maximum production efficiency of irrigation and the best quality of fruit could be achieved. In conclusion, treatment T4 was the optimum irrigation schedule for growing mango, thus achieving efficient production of mango in consideration of the compromise among mango yield, fruit quality and water use efficiency.

Molecular Cloning, Characterization, and Expression of MiSOC1: A Homolog of the Flowering Gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 from Mango (Mangifera indica L).

MADS-box transcription factor plays a crucial role in plant development, especially controlling the formation and development of floral organs. Mango (Mangifera indica L) is an economically important fruit crop, but its molecular control of flowering is largely unknown. To better understand the molecular basis of flowering regulation in mango, we isolated and characterized the MiSOC1, a putative mango orthologs for the Arabidopsis SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1/AGAMOUS-LIKE 20 (SOC1/AGL20) with homology-based cloning and RACE. The full-length cDNA (GenBank accession No.: KP404094) is 945 bp in length including a 74 bp long 5' UTR and a 189 bp long 3' UTR and the open reading frame was 733 bps, encoding 223 amino acids with molecular weight 25.6 kD. Both sequence alignment and phylogenetic analysis all indicated that deduced protein contained a conservative MADS-box and semi-conservative K domain and belonged to the SOC1/TM3 subfamily of the MADS-box family. Quantitative real-time PCR was performed to investigate the expression profiles of MiSOC1 gene in different tissues/organs including root, stem, leaves, flower bud, and flower. The result indicated MiSOC1 was widely expressed at different levels in both vegetative and reproductive tissues/organs with the highest expression level in the stems' leaves and inflorescences, low expression in roots and flowers. The expression of MiSOC1 in different flower developmental stages was different while same tissue -specific pattern among different varieties. In addition, MiSOC1 gene expression was affect by ethephon while high concentration ethephon inhibit the expression of MiSOC1. Overexpression of MiSOC1 resulted in early flowering in Arabidopsis. In conclusion, these results suggest that MiSOC1 may act as induce flower function in mango.

Cloning and characterization of an RNase-related protein gene preferentially expressed in rice stems.

RNase-related proteins (RRPs) are S- and S-like RNase homologs lacking the active site required for RNase activity. Here we describe the cloning and characterization of the rice (Oryza sativa) RRP gene (OsRRP). A single copy of OsRRP occurs in the rice genome. OsRRP contains three introns and an open reading frame encoding 252 amino acids, with the replacement of two histidines involved in the active site of RNase by lysine and tyrosine respectively. OsRRP is preferentially expressed in stems of wild-type rice and is significantly down-regulated in an increased tillering dwarf mutant ext37.