Functional studies of Arabidopsis FIN219 in cross-talks between blue light and far-red light signaling
Date Issued
2008
Date
2008
Author(s)
Fu, Tsu-Yu
Abstract
Arabidopsis thaliana seedlings undergo photomorphogenesis in the light and skotomorphogenesis (etiolation) in the dark. Photomorphogenesis is often regulated by red/far-red light-absorbing phytochromes and UV-A/blue light-absorbing cryptochromes. Far-red insensitive 219 (FIN219), a member of GH3 gene family, was previously shown to be involved in phytochrome A (phyA)-mediated far-red light signaling acting as an extragenic suppressor of constitutive photomorphogenic 1 (cop1). However, the gain of function of FIN219 exhibits a hypersensitive phenotype in response to far-red, blue and white light, which suggests that FIN219 might play a role in blue light signaling in addition to far-red light. Here we show that Arabidopsis cryptochrome 1 (CRY1) and its C-terminal domain (CCT1) physically interact with FIN219 protein in vitro. Subcellular localization studies in onion (Allium cepa) epidermal cells reveal that FIN219 localizes in both the nucleus and the cytosol and co-localizes with CRY1, cryptochrome 2 (CRY2) and COP1. In addition, FIN219 was rapidly induced by blue light treatment and this induction required functional CRY1 in vivo. To further elucidate the physiological functions of FIN219 in blue light signaling, a full-length FIN219 construct driven by 35S promoter was introduced into the blue light photoreceptor mutants, cry1, cry2 and cry1cry2, as well as GUS-CCT1 transgenic plants that overexpressed β-glucuronidase (GUS) and CCT1 fusion proteins showing a hyperphotomorphogenic development under all light conditions, including the darkness. The results revealed that ectopic expression of FIN219 in Arabidopsis blue light receptor mutant backgrounds, cry1, cry2 or cry1cry2, did not result in obvious phenotype, which implies that FIN219 requires the presence of CRY1 and CRY2 to regulate hypocotyl elongation under blue light. Moreover, GUS-CCT1 transgenic plants can be rescued by overexpression of a c-myc-FIN219 construct compared to wild-type phenotype under various light conditions. Nevertheless, in immunoblot analysis of FIN219-OE/GUS-CCT1 transgenic seedlings, we found that GUS-CCT1 and c-myc-FIN219 were hardly detectable. In contrast, GUS-CCT1 and c-myc-FIN219 mRNA transcripts in rescued seedlings can be detected, suggesting that c-myc-FIN219 and GUS-CCT1 fusion proteins might be antagonistically regulated in posttranscriptional modifications, leading to a rescued hypocotyl phenotype. Finally, we demonstrate that FIN219 is a positive regulator of Arabidopsis flowering under long-day condition. Taken together, the roles of FIN219 in regulating both of the de-etiolation and flowering responses may represent the integrated point where far-red light signaling and blue light signaling intersect.
Subjects
Arabidopsis
photomorphogenesis
hypocotyl
cryptochrome
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