The protective role of melatonin in plants under abiotic stress has been reported, but little information is available on its mitigation effect on coffee (Coffea arabica) plants. The objective of this study was to determine the effect of exogenous application of 100 µM melatonin in coffee leaves under 3 months of drought stress treatment. Melatonin was found to alleviate the drought-induced damage in coffee through reducing the rate of chlorophyll degradation, electrolyte leakage, malonaldehyde content, and activating various antioxidant enzymes, such as catalase, guaiacol peroxidase, and superoxide dismutase. Melatonin application suppressed the expression of chlorophyll degradation gene PAO encoding pheophorbide a oxygenase, and upregulated the expression of photosynthetic gene RBCS2 encoding ribulose-1,5-bisphosphate oxygenase (Rubisco) protein, and a drought-related gene AREB encoding abscisic acid-responsive element binding protein. The photosynthetic efficiency of photosystem II under dark adaptation was also improved upon melatonin application in drought-stressed plants. Our results showed that both foliar spray and direct soil application of melatonin could improve drought tolerance by regulating photosynthetic efficiency and oxidative damage in C. arabica seedlings. This study provides insights in application of melatonin as a protective agent against drought stress in improvement of crop yields.
The endosperm cell walls of mature coffee seeds accumulate large amounts of mannan storage polysaccharides, which serve as nutrient reserve for embryo and contribute to beverage quality. Our study investigated the evolutionary patterns of key galactomannan (GM) biosynthesis genes using dN/dS ratio, synteny, and phylogenetic analysis and detected heterogeneity in rate of evolution among gene copies. Selection ratio index revealed evidence of positive selection in the branch editing gene Coffea canephora alpha (α) galactosidase (Cc‐alpha Gal) at Cc11_g15950 copy (ω = 1.12), whereas strong purifying selection on deleterious mutations was observed in the Coffea canephora uridine diphosphate (UDP)‐glucose 4′‐epimerase (Cc‐UG4E) and Coffea canephora mannose‐1P guanylytransferase (Cc‐MGT) genes controlling the crucial nucleotide carbon sugar building blocks flux in the pathway. Relatively low sequence diversity and strong syntenic linkages were detected in all GM pathway genes except in Cc‐alpha Gal, which suggests a correlation between selection pressure and nucleotide diversity or synteny analysis. In addition, phylogenetic analysis revealed independent evolution or expansion of GM pathway genes in different plant species, with no obvious inferable clustering patterns according to either gene family or congruent with evolutionary plants lineages tested due to high dynamic nature and specific biochemical cell wall modification requirements. Altogether, our study shows a significant high rate of evolutionary variation among GM pathway genes in the diploid C. canephora and demonstrates the inherent variation in evolution of gene copies and their potential role in understanding selection rates in a homogenously connected metabolic pathway.
DICER-likes (DCLs) proteins are the core component for non-coding RNA (ncRNA) biogenesis, playing essential roles in some biological processes. The DCL family has been characterized in model plants, such as Arabidopsis, rice, and poplar. However, the evolutionary aspect and the expression mechanism under drought stress were scarce and have never been reported and characterized in one of the most important worldwide cultivated fruit trees, peach (Prunus persica). Eight DCLs genes in the Prunus persica genome were detected, in addition to 51 DCLs in the other seven Rosaceae genomes. The phylogenetic analysis with Arabidopsis thaliana and RTL1 gene as outgroups suggested that DCL members are divided into four clades: DCL1, DCL2, DCL3, and DCL4 with several gene gain/loss events of DCL gene copies through the evolutionary tract of the Rosacea family. The number of homologous DCL copies within each clade, along with the chromosomal location indicated gene duplication event of the DCL2 gene occurred once for the subfamily Amygdaloideae and twice for Pyrus communis and Prunus dulics and trice for the P. persica on Chromosome number 7 genes. Another duplication event was found for the DCL3 gene that occurred once for all the eight Rosaceae species with no match in A. thaliana. The DCL genetic similarity and activity was evaluated using BLASTp and previously published RNA-seq data among different tissues and over different time points of peach trees exposed to drought conditions. Finally, the expression pattern of PrupeDCLs in response to drought stress was identified, and two of these members, Prupe.7G047900 and Prupe.6G363600, were found as main candidate genes for response to drought stress. Our data presented here provide useful information for a better understanding of the molecular evolution of DCL genes in Rosaceae genomes, and the function of DCLs in P. persica.
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