Abstract
BackgroundEthylene-dependent gravitropism-deficient and yellow-green 1 (EGY1) protein is required for chloroplast development and photosynthesis conduction. The egy1 deletion mutants have a yellow-green phenotype and reduced granal thylakoids. Furthermore, the yellow-green phenotype of egy1 mutants is more obvious than that of wild-type (WT) plants with increasing leaf age, suggesting an early senescence in the egy1 mutants. However, the relationship between EGY1 functions and leaf senescence still remains poorly understood.ResultsWe observed that egy1 mutant leaves were more yellow than those of WT (the same age) in Arabidopsis thaliana. In accompany with this phenotype, leaf survival, chlorophyll content, Fv/Fm and soluble protein content decreased, and ion leakage increased significantly in egy1 mutants compared to WT plants. At molecular level, the expressions of senescence-associated genes increased, and photosynthesis genes decreased significantly in the mutants compared to those in WT plants. Furthermore, after darkness treatment, the yellow-green phenotype of egy1 mutants was more obvious than that of WT. These results indicate that the loss-of-function of egy1 gene induces leaf senescence in A. thaliana. In addition, our results showed that the yellow-green phenotype, chlorophyll content and ion leakage of egy1 mutants was partially restored after exogenously applied glucose for 5 weeks. At the same time, the expression of hexokinase 1 (HXK1) and/or senescence-associated gene 12 (SAG12) in egy1 mutants growing on 2 % glucose was lower than that in egy1 mutants without glucose.Conclusion EGY1-defection induced leaf senescence and this senescence was partially restored by glucose in A. thaliana.
Highlights
Ethylene-dependent gravitropism-deficient and yellow-green 1 (EGY1) protein is required for chloroplast development and photosynthesis conduction
The mutants of egy1 are such plants of Arabidopsis thaliana because EGY1 protein is required for chloroplast development and photosynthesis conduction (Chen et al 2005; Guo et al 2008), and the yellow-green phenotype of egy1 mutants is more obvious than that of wild-type (WT) plants with increasing leaf age
To study the effect of the T-DNA insertion on At5g35220 expression, we analyzed the results of RT-PCR, which showed that this gene was undetectable in the mutant, while it was normal expressed in WT plants (Fig. 1b)
Summary
Ethylene-dependent gravitropism-deficient and yellow-green 1 (EGY1) protein is required for chloroplast development and photosynthesis conduction. The yellow-green phenotype of egy mutants is more obvious than that of wild-type (WT) plants with increasing leaf age, suggesting an early senescence in the egy mutants. Its development stages include initiation, growth, differentiation, maturation and senescence. The last stage of leaf development, plays a key role in plant survival and/or death. Plant cells undergo orderly changes in structure, metabolism and gene expression (Buchanan-Wollaston et al 2003; Guiboileau et al 2010). Some external factors such as the alterations of nutrient, light and other environmental factors initiate leaf senescence (Guiboileau et al 2010; Ono et al 2001). Sugar signaling pathways are important regulation mechanisms for leaf senescence in plants (van Doorn 2008), which consists of glucose, sucrose, trehalose and other hexokinase-independent sugar signaling pathways (Smeekens et al 2009; Xiao et al 2000). Hexokinase 1 (HXK1) acts as the direct glucose sensor mediating multiple functions in the glucose repression and glucose promotion of transcription and growth (Cho et al 2006)
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