Impact of Plasma-Activated Water Treatment on Quality and Shelf-Life of Fresh Spinach Leaves Evaluated by Comprehensive Metabolomic Analysis

Circadian clock regulation in soybean senescence: a transcriptome analysis of early and late senescence types

BACKGROUND

Plant senescence is the process of physiological maturation of plants and is important for crop yield and quality. Senescence is controlled by several factors, such as temperature and photoperiod. However, the molecular basis by which these genes promote senescence in soybeans is not well understood. We identified senescence-related genes via transcriptome analysis of early-senescence (ES)- and late-senescence (LS)-type plants to elucidate the molecular mechanisms of senescence in soybeans.

RESULTS

We obtained early-senescence (ES)- and late-senescence (LS)-type F7 plants from a cross between a hybrid (Glycine max × Glycine soja) and the Glycine max cultivar. The ES-type plants presented the reproductive (R2) growth stage at 50 days after sowing (DAS) and the R7 growth stage at 95 DAS, whereas the LS-type plants presented the beginning of the R1 and R6 growth stages at 50 and 95 DAS, respectively. To understand the molecular mechanisms underlying this senescence, we performed transcriptome analysis of leaves from 50 to 95 DAS of ES- and LS-type plants. A total of 2,414 and 2,471 genes at 50 and 95 DAS, respectively, were differentially expressed between ES-type and LS-type plants. Twenty-three candidate genes associated with the circadian clock, chlorophyll biosynthesis, phytohormones, and senescence-associated protein kinases were identified, and their expression levels were analyzed. In addition, to understand interaction between circadian clock and senescence, we analyzed expression patterns of seven circadian clock-related genes during the time period (light and dark condition): CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), CONSTANS-LIKE 9 (COL9), LUX ARRHYTHMO (LUX) EARLY FLOWERING 3 (ELF3), PSEUDO-RESPONSE REGULATOR5 (PRR5) and GIGANTEA (GI). The expression patterns of circadian clock-related genes were similar in the ES- and LS-type plants. However, the transcription levels of these genes were compared between ES- and LS-type plants, and the expression of these genes was greater than that in LS-type plants during the period when expression increased. Therefore, each set of candidate genes regulated senescence in each plant by regulating their expression level.

CONCLUSIONS

These findings provide novel insights into the regulation of senescence in soybean plants, which could lead to the development of new strategies to improve agriculture.

Research progress on the relationship between leaf senescence and quality, yield and stress resistance in horticultural plants

Leaf senescence, the final stage of leaf development, is one of the adaptive mechanisms formed by plants over a long period of evolution. Leaf senescence is accompanied by various changes in cell structure, physiological metabolism, and gene expressions. This process is controlled by a variety of internal and external factors. Meanwhile, the genes and plant hormones involved in leaf aging affect the quality, yield and stress resistance in horticultural plants. Leaf senescence mediated by plant hormones affected plant quality at both pre-harvest and post-harvest stages. Exogenous plant growth regulators or plant hormone inhibitors has been applied to delay leaf senescence. Modification of related gene expression by over-expression or antisense inhibition could delay or accelerate leaf senescence, and thus influence quality. Environmental factors such as light, temperature and water status also trigger or delay leaf senescence. Delaying leaf senescence could increase chloroplast lifespan and photosynthesis and thus improve source strength, leading to enhanced yield. Accelerating leaf senescence promotes nutrient redistribution from old leaves into young leaves, and may raise yield under certain circumstances. Many genes and transcriptional factors involved in leaf senescence are associated with responses to abiotic and biotic stresses. WRKY transcriptional factors play a vital role in this process and they could interact with JA signalling. This review summarized how genes, plant hormones and environmental factors affect the quality, yield. Besides, the regulation of leaf senescence holds great promise to improving the resistance to plant biotic and abiotic stresses.