CRY1 inhibits COP1‐mediated degradation of BIT1, a MYB transcription factor, to activate blue light‐dependent gene expression in Arabidopsis

Abstract

SummaryCryptochromes (CRY) are one of the two major classes of photoreceptors that perceive light stimuli in the UV-A to blue light region and they are involved in multiple aspects of plant growth and development. However, knowledge regarding their signaling transduction components and mechanisms remains limited. Here, we report that a MYB transcription factor Blue Insensitive Trait 1 (BIT1), plays an important role in controlling blue light responses. Hypocotyl growth responses indicate that BIT1 functions as a positive element in blue light signaling, since BIT1 antisense and knock-out lines show a reduced light response in blue light. BIT1 controls blue light-dependent expression of various genes such as PsbS, a member of the light-harvesting complex gene family. A transactivation assay showed that BIT1 regulates promoter activity of PsbS in a blue lightdependent manner and that it requires CRY1 for activation of the PsbS promoter. BIT1 undergoes degradation in darkness and CRY1 functions to stabilize BIT1 in a blue light-dependent manner. In contrast, COP1 binds to BIT1 and mediates its degradation. We propose that the PsbS promoter is activated in blue light via the blue light-dependent stabilization of BIT1 by CRY1, while in darkness BIT1 is degraded by COP1-mediated proteolysis.

MdCOP1 Ubiquitin E3 Ligases Interact with MdMYB1 to Regulate Light-Induced Anthocyanin Biosynthesis and Red Fruit Coloration in Apple

“…Several photomorphogenesis-associated TFs are regulated by light not only at the transcript level but also at the posttranslational level (Hong et al, 2008). However, it is still unknown whether and how anthocyaninassociated MYB TFs are regulated at the posttranslational level in apple and other plant species.…”

“…The subcellular distribution of COP1 is adjusted according to light conditions. In darkness, COP1 is localized to the nucleus, where it presumably targets photomorphogenesis-promoting transcription factors (TFs), such as ELONGATED HYPOCOTYL5 (HY5), LONG AFTER FAR-RED1 (LAF1), LONG HY-POCOTYL IN FAR-RED1 (HFR1), BLUE INSENSITIVE TRAIT1 (BIT1), and CONSTANS (CO), and subsequently mediates their ubiquitination and degradation via the 26S proteasome pathway (Osterlund et al, 2000;Seo et al, 2003;Yang et al, 2005;Hong et al, 2008;Jang et al, 2008). When cells are exposed to light, there is a drastic reduction in COP1 abundance in the nucleus, allowing nuclear-localized TFs to reaccumulate.…”

“…Downstream of the light receptors, the ubiquitin E3 ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) acts as a molecular switch of light-induced plant development, such as photomorphogenesis (Osterlund et al, 2000;Holm et al, 2002;Seo et al, 2003;Hong et al, 2008), flowering time (Jang et al, 2008), photoperiodic growth (Yu et al, 2008), and stomatal development (Kang et al, 2009). The subcellular distribution of COP1 is adjusted according to light conditions.…”

COP1-Mediated Degradation of BBX22/LZF1 Optimizes Seedling Development in Arabidopsis

“…For example, the 26S proteasome regulates the accumulation of proteins for light perception and signaling (for review, see Henriques et al, 2009). COP1 is a wellknown E3 ligase functioning in selective degradation of proteins regulating many aspects of plant development, including photomorphogenesis (Ang et al, 1998;Osterlund et al, 2000b;Holm et al, 2002;Seo et al, 2003Seo et al, , 2004Jang et al, 2005;Hong et al, 2008), photoperiodic growth , and flowering time control (Jang et al, 2008;Liu et al, 2008). Although the importance of COP1 in photomorphogenic growth is well documented, the repertoire of light-signaling proteins targeted by COP1 is likely incomplete.…”

Molecular interactions of BBX24 and BBX25 with HYH, HY5 HOMOLOG, to modulateArabidopsisseedling development

“…14 Some of them integrate different light signals and function downstream to different photoreceptors such as HY5, CAM7, BBX21, BBX22, BBX24, BBX25 1,6,7 and other are involved in specific light signaling such as HYH, MYC2, GBF1, BIT1 that integrate signals from blue light [8][9][10][11] or LAF1, HFR1, FHY1 and FHL from far-red light. [12][13][14] In the light, the photoreceptors activate transcription factors such as HY5, HYH, CAM7, LAF1 and HFR1 by attenuating the BBX24 and BBX25 are two important transcriptional regulators, which regulate seedling photomorphogenesis in Arabidopsis.…”