The COP9 SIGNALOSOME Is Required for Postembryonic Meristem Maintenance in Arabidopsis thaliana

Abstract

Cullin-RING E3 ligases (CRLs) regulate different aspects of plant development and are activated by modification of their cullin subunit with the ubiquitin-like protein NEDD8 (NEural precursor cell expressed Developmentally Down-regulated 8) (neddylation) and deactivated by NEDD8 removal (deneddylation). The constitutively photomorphogenic9 (COP9) signalosome (CSN) acts as a molecular switch of CRLs activity by reverting their neddylation status, but its contribution to embryonic and early seedling development remains poorly characterized. Here, we analyzed the phenotypic defects of csn mutants and monitored the cullin deneddylation/neddylation ratio during embryonic and early seedling development. We show that while csn mutants can complete embryogenesis (albeit at a slower pace than wild-type) and are able to germinate (albeit at a reduced rate), they progressively lose meristem activity upon germination until they become unable to sustain growth. We also show that the majority of cullin proteins are progressively neddylated during the late stages of seed maturation and become deneddylated upon seed germination. This developmentally regulated shift in the cullin neddylation status is absent in csn mutants. We conclude that the CSN and its cullin deneddylation activity are required to sustain postembryonic meristem function in Arabidopsis.

The onset of embryo maturation in Arabidopsis is determined by its developmental stage and does not depend on endosperm cellularization

“…fus12 embryos grow at a slower rate than wild‐type ones, likely because the COP9 complex indirectly influences the cell cycle (Betsch et al ., ). The fus12 allele shows low maternal transmission, resulting in 15% or fewer mutant embryos in self‐pollinated heterozygous siliques (Franciosini et al ., ). til1‐4 is a strong hypomorphic allele of the gene coding for DNA polymerase epsilon.…”

“…For both mutants we first present the percentage of wild‐type and mutant embryos of different stages at each time point that expressed the marker under study (Figures and , panels a, d, g). fus12 and til1‐ 4 embryos show mild root pole defects starting at the early to mid‐globular stages (Jenik et al ., ; Franciosini et al ., ). To decide which embryos were mutant (those to the left of the red line in Figures and a,d,g), we scored for these defects and also considered the delay when compared to embryos in sibling wild‐type plants at that time point (Figures S3 and S4).…”

“…In fus12 seeds the endosperm cellularized at the same stage as in wild‐type seeds (Figure a and Table S2d), confirming our previous qualitative observations (Franciosini et al ., ). Because fus12 and wild‐type embryos also mature at the same stage, the correlation between cellularization and maturation holds in this case.…”

“…fus12 is seedling lethal (Franciosini et al ., ) and til1‐4 homozygotes have an extremely reduced seed set (Jenik et al ., ). Therefore, the comparisons presented below are always between homozygous mutant embryos and wild‐type embryos either from the same siliques or from sibling wild‐type plants grown at the same time.…”

Quantitative iTRAQ‐based proteomic analysis of rice grains to assess high night temperature stress

“…The COP9 signalosome is a conserved protein complex that is involved in regulating the activity of cullin-RING ligase families of ubiquitin E3 complexes in the ubiquitin-proteasome system [35]. The COP9 signalosome has been reported as a key player in DNA-damage response, cell-cycle control, and gene expression [36] and is also reported to sustain postembryonic meristem function in Arabidopsis [37]. A previous study showed that HNT is mainly influenced in endosperm development including endosperm cell number and size [11], and in present study, a COP9 signalosome complex subunit 3 (Q6ZJ47) showed a 4.6-fold upregulation in the HTL and was downregulated 1.5 (1/0.667)-fold in the HSL after HNT stress at early milky stage.…”