Plant Molecular Biology 52: 715–727, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
The Arabidopsis SKP1-like genes present a spectrum of expression proﬁles
Katia Marrocco, Alain Lecureuil, Pierre Nicolas and Philippe Guerche
Station de G´en´etique et d’Am´elioration des Plantes, Institut National de la Recherche Agronomique, Route de Saint
Cyr, 78026 Versailles cedex, France (
author for correspondence; e-mail email@example.com)
Received 14 February 2003; accepted 23 February 2003
Key words: Arabidopsis thaliana, expression proﬁles, GUS, SKP1-like
The yeast Skp1 protein is a component of the SCF complex, an E3 enzyme involved in the speciﬁc protein degrada-
tion pathway via ubiquitination. Skp1 binds to F-box proteins to trigger speciﬁc recognition of proteins targeted for
degradation. SKP1-like genes have been found in a variety of eukaryotes including yeast, man, Caenorhabditis ele-
gans and Arabidopsis thaliana.TheArabidopsis genome contains 20 SKP1-like genes called ASK (for Arabidopsis
SKP1-like), among which only ASK1 has been characterized in detail. The analysis of the expression pattern of the
ASK genes in Arabidopsis should provide key information for the understanding of the biological role of this family
in protein degradation and in different cellular mechanisms. In this paper, we describe the expression proﬁles of
19 ASK promoter-GUS fusions in stable transformants of Arabidopsis, with a special emphasis on ﬂoral organ
development. Four ASK promoters did not show any detectable expression in either inﬂorescences or seedlings.
Our results on the ASK1 expression proﬁle are consistent with previous reports. Several ASK promoters show clear
tissue-speciﬁc expression (for instance in the connective of anthers or in the embryo). We also found that almost
half (9/19) of ASK promoters direct a post-meiotic expression in the male gametophyte. Tight regulation of the
expression of this gene family indicates a crucial role of the ubiquitin degradation pathway during development,
particularly during male gametophyte development.
Abbreviations: ASK, Arabidopsis SKP1-like; GUS, β-glu
Most cellular functions in eukaryotes, including cell
cycle regulation, signal transduction, transcriptional
regulation or developmental processes, are tightly con-
trolled. In most cases, selective degradation of key
proteins constitutes an efﬁcient way of regulation.
The ubiquitin pathway appears to be a major sys-
tem for selective protein degradation in eukaryotic
cells. This pathway has been well studied in the yeast
Saccharomyces cerevisiae and consists of a three-
step mechanism: ﬁrst, an ubiquitin-activating enzyme
(E1) activates ubiquitin in an ATP-dependent manner.
Then, the activated ubiquitin is transferred to a sec-
ond enzyme, an ubiquitin-conjugating enzyme (E2).
The ﬁnal step that links the activated ubiquitin to
the target protein involves an ubiquitin-protein ligase
(E3), which acts as the speciﬁc factor responsible for
substrate recognition. Polyubiquitinated proteins are
then targeted to the 26S proteasome for degradation
(Hershko and Ciechanover, 1998; Ciechanover et al.,
The SCF complex is an E3 enzyme that has
been extensively studied in yeast, mammals and
plants. It involves four subunits, Skp1, Cullin/CDC53,
Rbx1/Roc1/Hrt1, which are three constant compo-
nents, and an F-box protein, which is a variable
component (Patton et al., 1998; Tyers and Jorgensen,
2000). Skp1 was ﬁrst identiﬁed as a protein involved
in the control of cell cycle progression (Zhang et al.,
1995; Connelly and Hieter, 1996; Bai et al., 1996).
Speciﬁc substrate recognition for ubiquitination re-
sults from the association of Skp1 with F-box proteins,
which constitute large families in all species. Several