Substitution of a conserved glycine in the PHR domain of arabidopsis CRYPTOCHROME 1 confers a constitutive light response

Abstract

CRYPTOCHROMES (CRYs) are photolyase-like ultraviolet-A/blue light photoreceptors that mediate various light responses in plants. The signaling mechanism of Arabidopsis CRYs (CRY1 and CRY2) involves direct CRY-COP1 interaction. Here, we report that CRY1G380R, which carries a Gly-to-Arg substitution of the highly conserved G380 in the photolyase-related (PHR) domain of Arabidopsis CRY1, shows constitutive CRY1 photoreceptor activity in Arabidopsis. Transgenic plants overexpressing CRY1G380R display a constitutively photomorphogenic (COP) phenotype in darkness, as well as a dramatic early flowering phenotype under short-day light conditions (SD). We further demonstrate that CRY1G380R expression driven by the native CRY1 promoter also results in a COP phenotype in darkness. Moreover, overexpression of either the Arabidopsis homolog CRY2G377R or the rice ortholog OsCRY1bG388R of CRY1G380R in Arabidopsis results in a COP phenotype in darkness. Cellular localization studies indicate that CRY1G380R co-localizes with COP1 in the same nuclear bodies (NBs) in vivo and inhibits the nuclear accumulation of COP1 in darkness. These results suggest that the conserved G380 may play a critical role in regulating the photoreceptor activity of plant CRYs and that CRY1G380R might constitutively phenocopy the photo-activated CRY1 in darkness and thus constitutively mediate CRY1 signaling. © 2011 The Author.