Abstract
The COP9 signalosome (CSN) is an evolutionary conserved multiprotein complex that regulates many aspects of plant development by controlling the activity of CULLIN-RING E3 ubiquitin ligases (CRLs). CRLs ubiquitinate and target for proteasomal degradation a vast number of specific substrate proteins involved in many developmental and physiological processes, including light and hormone signaling and cell division. As a consequence of CSN pleiotropic function, complete loss of CSN activity results in seedling lethality. Therefore, a detailed analysis of CSN physiological functions in adult Arabidopsis plants has been hampered by the early seedling lethality of csn null mutants. Here we report the identification and characterization of a viable allele of the Arabidopsis COP9 signalosome subunit 4 (CSN4). The allele, designated csn4-2035, suppresses the adventitious root (AR) phenotype of the Arabidopsis superroot2-1 mutant, potentially by altering its auxin signaling. Furthermore, we show that although the csn4-2035 mutation affects primary and lateral root (LR) formation in the 2035 suppressor mutant, CSN4 and other subunits of the COP9 complex seem to differentially control AR and LR development.
Highlights
The COP9 signalosome (CSN) was first discovered in Arabidopsis, during a screening for mutants exhibiting constitutive photomorphogenic development in darkness, and was subsequently shown to be evolutionary conserved across eukaryotes
It has been suggested that one potential reason for the lack of viable known csn mutants is that CSN-independent functions of CSN subunits can only be uncovered under specific conditions[4], and probably in particular types of screening
Aiming to identify new Arabidopsis genes involved in the control of adventitious root (AR) formation, we screened for suppressors of the superroot[] mutant[10]
Summary
The CSN was first discovered in Arabidopsis, during a screening for mutants exhibiting constitutive photomorphogenic development in darkness, and was subsequently shown to be evolutionary conserved across eukaryotes (reviewed in ref. 1). The AR formation was almost completely abolished in the csn4-2035 single mutant compared to the Ws-4 wild-type, since the majority of the seedlings had no initiated AR on the hypocotyl seven days after being transferred to the light, and only a limited number of individuals developed one AR (Fig. 2a,c).
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