Abstract
The Pathogen and Circadian Controlled 1 (PCC1) gene, previously identified and further characterized as involved in defense to pathogens and stress-induced flowering, codes for an 81-amino acid protein with a cysteine-rich C-terminal domain. This domain is essential for homodimerization and anchoring to the plasma membrane. Transgenic plants with the ß-glucuronidase (GUS) reporter gene under the control of 1.1 kb promoter sequence of PCC1 gene display a dual pattern of expression. At early post-germination, PCC1 is expressed only in the root vasculature and in the stomata guard cells of cotyledons. During the transition from vegetative to reproductive development, PCC1 is strongly expressed in the vascular tissue of petioles and basal part of the leaf, and it further spreads to the whole limb in fully expanded leaves. This developmental pattern of expression together with the late flowering phenotype of long-day grown RNA interference (iPCC1) plants with reduced PCC1 expression pointed to a regulatory role of PCC1 in the photoperiod-dependent flowering pathway. iPCC1 plants are defective in light perception and signaling but are not impaired in the function of the core CO-FT module of the photoperiod-dependent pathway. The regulatory effect exerted by PCC1 on the transition to flowering as well as on other reported phenotypes might be explained by a mechanism involving the interaction with the subunit 5 of the COP9 signalosome (CSN).
Highlights
The Pathogen and Circadian Controlled 1 (PCC1) gene in Arabidopsis was originally identified as a Pseudomonas syringae-induced gene with a circadian controlled pattern of expression [1]
We generated constructs to transiently express recombinant versions of PCC1 protein fused in its N- and C-terminus to GFP under the 35S promoter in Nicotiana benthamiana
The typical fluorescence associated to the plasma membrane of the PCC1-GFP protein was changed to cytoplasmic and nuclear localization for the truncated version lacking the C-terminus (Fig. 1D), confirming the essential role for the C-terminus to be anchored to the plasma membrane
Summary
The Pathogen and Circadian Controlled 1 (PCC1) gene in Arabidopsis was originally identified as a Pseudomonas syringae-induced gene with a circadian controlled pattern of expression [1]. Gibberellins (GAs) are key hormones in many light-driven transitions [5] including seed germination [6], hypocotyl elongation during skotomorphogenesis [7,8] and flowering time [9]. Cullin must be posttranslationally modified by binding the RUB/NEDD8 ubiquitinlike protein for SCF complexes to be assembled and fully active [15]. This ubiquitination machinery is negatively controlled by the function of an eight-subunit protein complex so-called COP9 signalosome (CSN), which has RUB isopeptidase activity that removes RUB modification from cullin proteins [16]. The derubylation reaction is mediated by the subunit CSN5, a zinc metalloprotease, defective function of any of the subunits make CSN unable in derubylation [17] and cause severe developmental [18] and defense responses [19]
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