CONSTITUTIVELY PHOTOMORPHOGENIC1 Is Required for the UV-B Response in Arabidopsis

Abstract

CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) is a negative regulator of photomorphogenesis in Arabidopsis thaliana. COP1 functions as an E3 ubiquitin ligase, targeting select proteins for proteasomal degradation in plants as well as in mammals. Among its substrates is the basic domain/leucine zipper (bZIP) transcription factor ELONGATED HYPOCOTYL5 (HY5), one of the key regulators of photomorphogenesis under all light qualities, including UV-B responses required for tolerance to this environmental threat. Here, we report that, in contrast with the situation in visible light, COP1 is a critical positive regulator of responses to low levels of UV-B. We show that in the cop1-4 mutant, flavonoid accumulation and genome-wide expression changes in response to UV-B are blocked to a large extent. COP1 is required for HY5 gene activation, and both COP1 and HY5 proteins accumulate in the nucleus under supplementary UV-B. SUPPRESSOR OF PHYTOCHROME A-105 family proteins (SPA1 to SPA4) that are required for COP1 function in dark and visible light are not essential in the response to UV-B. We conclude that COP1 performs a specific and novel role in the plants' photomorphogenic response to UV-B, coordinating HY5-dependent and -independent pathways, which eventually results in UV-B tolerance.

Retracted: Nitric oxide enhances plant ultraviolet‐B protection up‐regulating gene expression of the phenylpropanoid biosynthetic pathway

“…Among the R2R3 MYB, it has been demonstrated that the maize P gene (ZmP) and its Arabidopsis functional homolog MYB12 control the transcriptional activation of the phenylpropanoid biosynthetic genes chalcone synthase (CHS), chalcone isomerase (CHI), flavonone 3-hydroxylase (F3H) and flavonol synthase 1 (FLS1) (Grotewold 2005;Mehrtens et al 2005;Luo et al 2008). Furthermore, it was reported that ZmP as well as MYB12 are up-regulated by UV-B exposure (Casati & Walbot 2005;Oravecz et al 2006).…”

Flavonoid Profiling and Biosynthetic Gene Expression in Flesh and Peel of Two Tomato Genotypes Grown under UV-B-Depleted Conditions during Ripening

“…Recently, Suesslin and Frohnmeyer (8) discovered a putative UV-B photoreceptor or, at least, an important component of the UV-B transduction signaling. This finding contributes, together with other important data (9)(10)(11), to better clarify the postulated existence of a stress-independent UV-B signaling pathway in plants. On the contrary, it is established that plant phytochromes and cryptochromes are not the UV-B photoreceptors, even if UV-A may play a role in UV-B signal transduction (12).…”

Arabidopsis STO/BBX24 negatively regulates UV-B signaling by interacting with COP1 and repressing HY5 transcriptional activity

“…The function of COP1 as an E3 ubiquitin ligase is impeded by light, resulting in activation of positive transcription factors to promote light response [10]. However, COP1 is a critical positive regulator of UV-B responses, contrasting to its function in light signaling [12]. HY5 is another important component shared by light and UV-B signaling.…”

“…HY5 is another important component shared by light and UV-B signaling. It is a bZIP transcription factor that positively regulates light-responsive gene expression [11], and it is required for plant survival under UV-B radiation [12]. COP1 is required for UV-B-induced HY5 gene activation, and both COP1 and HY5 proteins accumulate in the nucleus under UV-B [12], suggesting that HY5 is not the target of COP1 for degradation in UV-B signaling.…”

“…It is a bZIP transcription factor that positively regulates light-responsive gene expression [11], and it is required for plant survival under UV-B radiation [12]. COP1 is required for UV-B-induced HY5 gene activation, and both COP1 and HY5 proteins accumulate in the nucleus under UV-B [12], suggesting that HY5 is not the target of COP1 for degradation in UV-B signaling. It is proposed that COP1 may function to remove a negative regulator of UV-B responses [12], but no such component has been described.…”