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Light exposure of Arabidopsis seedlings causes rapid de‐stabilization as well as selective post‐translational inactivation of the repressor of photomorphogenesis SPA2
Author(s) -
Balcerowicz Martin,
Fittinghoff Kirsten,
Wirthmueller Lennart,
Maier Alexander,
Fackendahl Petra,
Fiene Gabriele,
Koncz Csaba,
Hoecker Ute
Publication year - 2011
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2010.04456.x
Subject(s) - photomorphogenesis , repressor , subfunctionalization , gene , ubiquitin ligase , biology , genetics , microbiology and biotechnology , arabidopsis , gene family , ubiquitin , gene expression , mutant
Summary The COP1/SPA complex acts as an E3 ubiquitin ligase to repress photomorphogenesis by targeting activators of the light response for degradation. Genetic analysis has shown that the four members of the SPA gene family ( SPA1–SPA4 ) have overlapping but distinct functions. In particular, SPA1 and SPA2 differ in that SPA1 encodes a potent repressor in light‐ and dark‐grown seedlings, but SPA2 fully loses its function when seedlings are exposed to light, indicating that SPA2 function is hyper‐inactivated by light. Here, we have used chimeric SPA1/SPA2 constructs to show that the distinct functions of SPA1 and SPA2 genes in light‐grown seedlings are due to the SPA protein sequences and independent of the SPA promoter sequences. Biochemical analysis of SPA1 and SPA2 protein levels shows that light exposure leads to rapid proteasomal degradation of SPA2, and, more weakly, of SPA1, but not of COP1. This suggests that light inactivates the COP1/SPA complex partly by reducing SPA protein levels. Although SPA2 was more strongly degraded than SPA1, this was not the sole reason for the lack of SPA2 function in the light. We found that the SPA2 protein is inherently incapable of repressing photomorphogenesis in light‐grown seedlings. The data therefore indicate that light inactivates the function of SPA2 through a post‐translational mechanism that eliminates the activity of the remaining SPA2 protein in the cell.