Abstract
There is growing evidence to suggest that epigenetic tags, especially DNA methylation, are critical regulators of fruit ripening. To examine whether this is the case in sweet pepper (Capsicum annuum) we conducted experiments at the transcriptional, epigenetic, and physiological levels. McrBC PCR, bisulfite sequencing, and real-time PCR demonstrated that DNA hypomethylation occurred in the upstream region of the transcription start site of some genes related to pepper ripening at the turning stage, which may be attributed to up-regulation of CaDML2-like and down-regulation of CaMET1-like1, CaMET1-like2, CaCMT2-like, and CaCMT4-like. Silencing of CaMET1-like1 by virus-induced gene silencing led to DNA hypomethylation, increased content of soluble solids, and accumulation of carotenoids in the fruit, which was accompanied by changes in expression of genes involved in capsanthin/capsorubin biosynthesis, cell wall degradation, and phytohormone metabolism and signaling. Endogenous ABA increased during fruit ripening, whereas endogenous IAA showed an opposite trend. No ethylene signal was detected during ripening. DNA hypomethylation repressed the expression of auxin and gibberellin biosynthesis genes as well as cytokinin degradation genes, but induced the expression of ABA biosynthesis genes. In mature-green pericarp, exogenous ABA induced expression of CaDML2-like but repressed that of CaCMT4-like. IAA treatment promoted the transcription of CaMET1-like1 and CaCMT3-like. Ethephon significantly up-regulated the expression of CaDML2-like. Treatment with GA3 and 6-BA showed indistinct effects on DNA methylation at the transcriptional level. On the basis of the results, a model is proposed that suggests a high likelihood of a role for DNA methylation in the regulation of ripening in the non-climacteric pepper fruit.
Highlights
McrBC PCR, bisulfite sequencing, and real-time PCR demonstrated that DNA hypomethylation occurred in the upstream region of the transcription start site of some genes related to pepper ripening at the turning stage, which may be attributed to up-regulation of CaDML2-like and down-regulation of CaMET1-like1, CaMET1-like2, CaCMT2-like, and CaCMT4-like
DNA methylation, phytohormones, and ripening of pepper fruit | 1929 is catalysed by CHROMOMETHYLASE 2 (CMT2) and DOMAIN REARRANGED METHYLTRANSFERASES (DRM1 and DRM2) through the RNA-directed DNA methylation (RdDM) pathway, whereas the symmetric type is catalysed by METHYLTRANSFERASE 1 (MET1) and CHROMOMETHYLASE 3 (CMT3) (Finnegan and Kovac, 2000; Lindroth et al, 2001; Bender, 2004; Zhang et al, 2010; Deleris et al, 2016)
Consistent with this, we found that exogenous ABA promoted carotenoid biosynthesis, cell wall degradation, and DNA hypomethylation through altering the expression of CaPYS1, CaPG, and genes related to DNA methylation (CaDML2-like and CaCMT4like), respectively (Figs 5A, Fig. 6)
Summary
The ripening of fleshy fruit involves an elaborate process that is regulated by many factors at multiple levels.There is growing evidence to suggest that epigenetic tags are a critical regulator of fruit ripening, especially DNA methylation (Zhong et al, 2013; Liu et al, 2015; Lang et al, 2017; Cheng et al, 2018).DNA methylation mainly refers to the methyl at the 5 ́ position of cytosine (5mC) (Bender, 2004). Expressed genes regulated by ripening-associated changes in DNA methylation are usually enriched in the processes of pigment biosynthesis (such as anthocyanin biosynthesis in strawberry and carotenoid biosynthesis in tomato), aromatic compound biosynthesis, cell wall degradation, and ripeningrelated phytohormone biosynthesis (such as ABA biosynthesis in strawberry and sweet orange, and ethylene biosynthesis in tomato) (Lang et al, 2017; Cheng et al, 2018; Huang et al, 2019). In the peel of sweet orange, ripening-associated DNA hypermethylation is primarily caused by the down-regulation of DNA demethylase genes (Huang et al, 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
