Abstract
The unique member of the calmodulin gene family, Calmodulin7 (CAM7), plays a crucial role as transcriptional regulator to promote Arabidopsis seedling development. CAM7 regulates the expression of HY5, which is intimately involved in the promotion of photomorphogenic growth and light‐regulated gene expression. COP1 ubiquitin ligase suppresses photomorphogenesis by degrading multiple photomorphogenesis promoting factors including HY5 in darkness. Genetic interaction studies, in this report, reveal that CAM7 and COP1 co‐ordinately work to promote photomorphogenic growth and light‐regulated gene expression at lower intensity of light. CAM7 physically interacts with COP1 in the nucleus. Further, in vivo study suggests that CAM7 and COP1 interaction is light intensity dependent. We have also shown that functional COP1 is required for optimum accumulation of CAM7 at lower fluences of light. Taken together, this study demonstrates the coordinated function of CAM7 and COP1 in Arabidopsis seedling development.
Highlights
Light controls multiple developmental processes in plant life cycle (Deng & Quail, 1999; Franklin & Quail, 2010; Jiao, Lau, & Deng, 2007; Kami, Lorrain, Hornitschek, & Fankhauser, 2010; Wang & Deng, 2003)
Our data strongly suggest that CAM7 and COP1 ge‐ netically and physically interact with each other and work in a co‐ operative manner. While their genetic interactions show an additive role of CAM7 and COP1, molecularly CAM7 is stabilized by COP1 at a lower intensity of light for promotion of photomorphogenesis
The HY5 level is low at lower fluences of white light (WL) and once HY5 level increases with higher intensity of light, it binds to its own promoter to enhance its expression (Abbas et al, 2014; Osterlund et al, 2000)
Summary
Light controls multiple developmental processes in plant life cycle (Deng & Quail, 1999; Franklin & Quail, 2010; Jiao, Lau, & Deng, 2007; Kami, Lorrain, Hornitschek, & Fankhauser, 2010; Wang & Deng, 2003). In Arabidopsis, seven genes encode four CAM isoforms, of which CAM1/CAM4 dif‐ fer by four amino acid substitutions from CAM7, whereas CAM2/3/5 and CAM6 differ by one amino acid position as compared to CAM7 (Mc Cormack et al, 2005) Among these seven bona fide calmodulin proteins in Arabidopsis, CAM7/ZBF3 binds to the Z‐ and G‐box of light‐regulated promoters (Kushwaha, Singh, & Chattopadhyay, 2008). ELONGATED HYPOCOTYL5 (HY5), a constitutively nuclear localized bZIP transcription factor, has been shown to func‐ tion as a positive regulator of photomorphogenesis under various wavelengths of light, including red, far‐red, and blue light, and more recently in UV‐B light as well (Binkert et al, 2014; Chattopadhyay, Puente, Deng, & Wei, 1998; Osterlund, Hardtke, Wei, & Deng, 2000; Oyama, Shimura, & Okada, 1997; Ulm et al, 2004). While their genetic interactions show an additive role of CAM7 and COP1, molecularly CAM7 is stabilized by COP1 at a lower intensity of light for promotion of photomorphogenesis
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