Genome-wide identification, characterization and expression profile of glutaredoxin gene family in relation to fruit ripening and response to abiotic and biotic stresses in banana (Musa acuminata)

Physiological and Transcriptomic Analyses Reveal the Mechanisms Underlying Methyl Jasmonate-Induced Mannitol Stress Resistance in Banana

Exogenous methyl jasmonate (MeJA) application has shown promising effects on plant defense under diverse abiotic stresses. However, the mechanisms underlying MeJA-induced stress resistance in bananas are unclear. Therefore, in this study, we treated banana plants with 100 μM MeJA before inducing osmotic stress using mannitol. Plant phenotype and antioxidant enzyme activity results demonstrated that MeJA improved osmotic stress resistance in banana plants. Thereafter, to explore the molecular mechanisms underlying MeJA-induced osmotic stress resistance in banana seedlings, we conducted high-throughput RNA sequencing (RNA-seq) using leaf and root samples of "Brazilian" banana seedlings treated with MeJA for 0 h and 8 h. RNA-seq analysis showed that MeJA treatment upregulated 1506 (leaf) and 3341 (root) genes and downregulated 1768 (leaf) and 4625 (root) genes. Then, we performed gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses on the differentially expressed genes. We noted that linoleic acid metabolism was enriched in both root and leaf samples, and the genes of this pathway exhibited different expression patterns; 9S-LOX genes were highly induced by MeJA in the leaves, whereas 13S-LOX genes were highly induced in the roots. We also identified the promoters of these genes, as the differences in response elements may contribute to tissue-specific gene expression in response to MeJA application in banana seedlings. Overall, the findings of this study provide insights into the mechanisms underlying abiotic stress resistance in banana that may aid in the improvement of banana varieties relying on molecular breeding.

Identification and adaptive evolution analysis of glutaredoxin genes in Populus spp

Glutaredoxin (GRX) is a class of small redox proteins widely involved in cellular redox homeostasis and the regulation of various cellular processes. The role of GRX gene in the differentiation of Populus spp. is rarely reported. We compared the similarities and differences of GRX genes among four sections of poplar using bioinformatics, corrected the annotations of some GRX genes, and focused on analysing their transcript profiling and adaptive evolution in Populus spp. A total of 219 GRX genes were identified in four sections of poplar, among which annotations for 13 genes were corrected. Differences in GRX genes were found between sect. Turanga, represented by P. euphratica, and other poplar sections. Most notably, P. euphratica had the smallest number of duplication events for GRX genes (n = 9) and no tandem duplications, whereas there were >25 duplication events for all other poplars. Furthermore, we detected 18 pairs of GRX genes under positive selection pressure in various sections of poplar, and identified two groups of GRX genes in the Salicaceae that potentially underwent positive selection. Expression profiling results showed that the PtrGRX34 and its orthologous genes were upregulated under stress treatments. In summary, the GRX gene family underwent expansion during poplar differentiation, and some genes underwent rapid evolution during this process, which may be beneficial for Populus spp. to adapt to environmental changes. This study may provide more insights into the molecular mechanisms of Populus spp. adaptation to environmental changes and the adaptive evolution of GRX genes.

Glutaredoxin in Rice Growth, Development, and Stress Resistance: Mechanisms and Research Advances

Rice (Oryza sativa L.) is a staple food for more than half of the global population. Various abiotic and biotic stresses lead to accumulation of reactive oxygen species in rice, which damage macromolecules and signaling pathways. Rice has evolved a variety of antioxidant systems, including glutaredoxin (GRX), that protect against various stressors. A total of 48 GRX gene loci have been identified on 11 of the 12 chromosomes of the rice genome; none were found on chromosome 9. GRX proteins were classified into four categories according to their active sites: CPYC, CGFS, CC, and GRL. In this paper, we summarized the recent research advances regarding the roles of GRX in rice development regulation and response to stresses, and discussed future research perspectives related to rice production. This review could provide information for rice researchers on the current status of the GRX and serve as guidance for breeding superior varieties.

Fumonisin B1 Biosynthesis Is Associated with Oxidative Stress and Plays an Important Role in Fusarium proliferatum Infection on Banana Fruit

Fungal response to oxidative stress during infection on postharvest fruit is largely unknown. Here, we found that hydrogen peroxide (H₂O₂) treatment inhibited the growth of Fusarium proliferatum causing crown rot of banana fruit, confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. H₂O₂ exposure increased endogenous reactive oxygen species (ROS) and fumonisin B1 (FB1) production in F. proliferatum, possibly by modulating FUM or ROS-related gene expression. Importantly, H₂O₂ treatment inhibited F. proliferatum growth in vivo but induced FB1 accumulation in banana peel. Finally, we constructed the FpFUM21 deletion mutant (ΔFpfum21) of F. proliferatum that was attenuated in FB1 biosynthesis and less tolerant to oxidative stress. Moreover, the ΔFpfum21 strain was less virulent compared to the wild type (WT) due to the inability to induce FB1 production in the banana host. These results suggested that FB1 biosynthesis is associated with oxidative stress in F. proliferatum and contributes to fungal infection on banana fruit.

Mining for salt-tolerant genes from halophyte Zoysia matrella using FOX system and functional analysis of ZmGnTL

Zoysia matrella is a salt-tolerant turfgrass grown in areas with high soil salinity irrigated with effluent water. Previous studies focused on explaining the regulatory mechanism of Z. matrella salt-tolerance at phenotypic and physiological levels. However, the molecular mechanism associated with salt tolerance of Z. matrella remained unclear. In this study, a high-efficient method named FOX (full-length cDNA overexpression) hunting system was used to search for salt-tolerant genes in Z. matrella. Eleven candidate genes, including several known or novel salt-tolerant genes involved in different metabolism pathways, were identified. These genes exhibited inducible expression under salt stress condition. Furthermore, a novel salt-inducible candidate gene ZmGnTL was transformed into Arabidopsis for functional analysis. ZmGnTL improved salt-tolerance through regulating ion homeostasis, reactive oxygen species scavenging, and osmotic adjustment. In summary, we demonstrated that FOX is a reliable system for discovering novel genes relevant to salt tolerance and several candidate genes were identified from Z. matrella that can assist molecular breeding for plant salt-tolerance improvement.

Genome-Wide Identification of Membrane-Bound Fatty Acid Desaturase Genes in Three Peanut Species and Their Expression in Arachis hypogaea during Drought Stress

As a crop irrigated primarily by rain, the quality and yield of peanuts are significantly limited by drought. To date, many studies have indicated that fatty acid desaturase (FAD) genes enhance plant tolerance to drought stresses. In this study, 16, 15, and 31 FADs were identified in Arachis duranensis, Arachis ipaensis, and Arachis hypogaea, respectively. All the FADs were divided into four subfamilies, which had relatively conserved gene structures, motifs, and domains. The synteny relationships and chromosomal position analysis showed that the FADs in subgenome pairs, A. duranensis-A. hypogaea (AA) and A. ipaensis-A. hypogaea (BB), were homologous, and their physical locations were consistent. The Ka/Ks results indicated that nine FAD genes underwent a purifying selection, and Ah|FAD3.2 experienced positive selection during tetraploid peanut speciation. Various cis-acting elements related to hormone signaling and stress responsiveness in promoters and the predicted miRNA targeting Ah|FADs suggested that these genes play crucial roles in drought tolerance. The expression profiles of Ah|FADs in 22 tissues and drought-tolerant and -sensitive cultivars under drought stress suggested that 4 and 6 FADs were putative genes related to oil accumulation and drought, respectively. These findings will help provide insight into the potential functional roles of the FAD genes, which may aid in dealing with plant drought stress.

Whole Transcriptome Analyses of Apricots and Japanese Plum Fruits after 1-MCP (Ethylene-Inhibitor) and Ethrel (Ethylene-Precursor) Treatments Reveal New Insights into the Physiology of the Ripening Process

The physiology of Prunus fruit ripening is a complex and not completely understood process. To improve this knowledge, postharvest behavior during the shelf-life period at the transcriptomic level has been studied using high-throughput sequencing analysis (RNA-Seq). Monitoring of fruits has been analyzed after different ethylene regulator treatments, including 1-MCP (ethylene-inhibitor) and Ethrel (ethylene-precursor) in two contrasting selected apricot (Prunus armeniaca L.) and Japanese plum (P. salicina L.) cultivars, ‘Goldrich’ and ‘Santa Rosa’. KEEG and protein–protein interaction network analysis unveiled that the most significant metabolic pathways involved in the ripening process were photosynthesis and plant hormone signal transduction. In addition, previously discovered genes linked to fruit ripening, such as pectinesterase or auxin-responsive protein, have been confirmed as the main genes involved in this process. Genes encoding pectinesterase in the pentose and glucuronate interconversions pathway were the most overexpressed in both species, being upregulated by Ethrel. On the other hand, auxin-responsive protein IAA and aquaporin PIP were both upregulated by 1-MCP in ‘Goldrich’ and ‘Santa Rosa’, respectively. Results also showed the upregulation of chitinase and glutaredoxin 3 after Ethrel treatment in ‘Goldrich’ and ‘Santa Rosa’, respectively, while photosystem I subunit V psaG (photosynthesis) was upregulated after 1-MCP in both species. Furthermore, the overexpression of genes encoding GDP-L-galactose and ferredoxin in the ascorbate and aldarate metabolism and photosynthesis pathways caused by 1-MCP favored antioxidant activity and therefore slowed down the fruit senescence process.

Dissipation and Distribution of Prochloraz in Bananas and a Risk Assessment of Its Dietary Intake

BACKGROUND

As a systematic fungicide, prochloraz is often used to control banana freckle disease, and it is significant to assess the safety and risk of prochloraz.

METHODS

The dissipation kinetics and distribution of prochloraz in bananas were measured by high-performance liquid chromatography (HPLC).

RESULTS

The results showed that the fortified recoveries in bananas were 83.01-99.12%, and the relative standard deviations (RSDs) were 2.45-7.84%. The half-life of prochloraz in banana peel (3.93-5.60 d) was significantly lower than it was in whole banana (8.25-10.80 d) and banana pulp (10.35-12.84 d). The terminal residue of prochloraz in banana fruits was below the maximum residue level (MRL, China) at pre-harvest intervals (PHI) of 21 d. Moreover, the residue of prochloraz in banana peel was always 1.06-7.71 times greater than it was in banana pulp. The dietary risk assessment results indicated that the prochloraz residue in bananas at PHI of 21 d was safe for representative populations. (4) Conclusions: We found that a 26.7% prochloraz emulsion oil in water (EW) diluted 1000-fold and sprayed three times under field conditions was safe and reliable, providing a reference for the safe application of prochloraz in bananas.

Proteomic and physiological analysis provides an elucidation of Fusarium proliferatum infection causing crown rot on banana fruit

Fusarium proliferatum causes the crown rot of harvested banana fruit but the underling infection mechanism remains unclear. Here, proteomic changes of the banana peel with and without inoculation of F. proliferatum were evaluated. In addition, we investigated the effects of F. proliferatum infection on cell structure, hormone content, primary metabolites and defense-related enzyme activities in the banana peel. Our results showed that F. proliferatum infection mainly affects cell wall components and inhibits the activities of polyphenoloxidase, peroxidase, and chitinase. Gel free quantitative proteomic analysis showed 92 down-regulated and 29 up-regulated proteins of banana peel after F. proliferatum infection. These proteins were mainly related to defense response to biotic stress, chloroplast structure and function, JA signaling pathway, and primary metabolism. Although jasmonic acid (JA) content and JA signaling component coronatine-insensitive (COI) protein were induced by F. proliferatum infection, JA-responsible defense genes/proteins were downregulated. In contrast, expression of senescence-related genes was induced by F. proliferatum, indicating that F. proliferatum modulated the JA signaling to accelerate the senescence of banana fruit. Additionally, salicylic acid (SA) content and SA signaling for resistance acquisition were inhibited by F. proliferatum. Taken together, these results suggest that F. proliferatum depolymerizes the cell wall barrier, impairs the defense system in banana fruit, and activates non-defensive JA-signaling pathway accelerated the senescence of banana fruit. This study provided the elucidation of the prominent pathways disturbed by F. proliferatum in banana fruit, which will facilitate the development of a new strategy to control crown rot of banana fruit and improvement of banana cultivars.