15th International Conference on Arabidopsis Research - TAIR

T01-093
SHI family genes redundantly regulate gynoecium
and leaf development in Arabidopsis
Sandra Kuusk(1, 2), Joel Sohlberg(1, 3), Mattias Myrenås(3), Magnus Eklund(3), Eva
Sundberg(1, 3)
1-Department of Physiological Botany, Evolutionary Biology Centre, Uppsala University, Villavägen
6, S-752 36 Uppsala, Sweden
2-Department of Cell and Molecular Biology, Biomedical centre, Uppsala University, Box 596,
S-751 24 Uppsala, Sweden
3-Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Science, Box
7080, S-750 07 Uppsala, Sweden
The SHI gene family comprises nine expressed members in Arabidopsis,
STY1, STY2, SHI, LRP1 and SRS3 to SRS7, and one putative pseudogene,
SRS8 (Fridborg et al. 2001; Kuusk et al 2002). These genes are highly
divergent in sequence, except for in two conserved regions; one encoding
a RING finger-like zinc finger domain and the other encoding a domain of
unknown function. At least six of the SHI-related genes redundantly regulate
the development of gynoecia, stamens and leaves. In sty1-1 mutants, the
gynoecia form aberrant apical tissues and exhibit distorted vascular patterning
(Kuusk et al 2002) whereas mutations in STY2, SHI, SRS3, SRS4, SRS5
and LRP1 have no apparent effect on gynoecium development. The sty1-1
gynoecia phenotype is, however, enhanced in the sty2-1, shi-3, srs4-2,
srs5-1 and lrp1 mutant backgrounds, and triple, quadruple and pentuple
mutants show that the consecutive knockout of SHI-related genes correlates
with increases in gynoecium abnormalities. In sty2-1 mutants, the leaves
are more serrated compared to the leaves of wild type and other SHI family
mutants studied. Quadruple and pentuple mutants reveal that several of the
SHI-related genes redundantly affect leaf morphogenesis. In accordance with
the gynoecium and leaf phenotypes, these genes are active in developing
gynoecia and young leaves, but exhibit distinct temporal, and/or spatial,
expression patterns. The genes are also expressed in other organs such
as lateral root primordia and root tips. Lateral root formation in 35S::STY1
plants is dramatically reduced and becomes restored to that of wild type by
exogenous auxin application. One interpretation could be that the level or
distribution of auxin, and not the auxin sensitivity or perception, in 35S::STY1
roots are suboptimal. Moreover, sty1-1 sty2-1 mutants are hypersensitive to
reductions in polar auxin transport (PAT) in the gynoecia and STY1 activates
at least two auxin inducible genes. These data suggest that SHI family genes
affect auxin regulated processes.
Fridborg et al. (2001) Plant Physiol. 127, 937-948
Kuusk et al. (2002) Development 129, 4707-4717
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T01-094
Mutations in the Arabidopsis FLAKY POLLEN gene
cause both sporophytic and gametophytic male
sterility
Sumie Ishiguro(1), Miho Yamada(2), Yuka Nishimori(1), Kiyotaka Okada(2), Kenzo
Nakamura(1)
1-Department of Cellular Mechanisms and Functions, Graduate School of Bio-Agricultural Sciences,
Nagoya University, Nagoya 464-8601, Japan
2-Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
A recessive male-sterile mutant of Arabidopsis was isolated from a
T-DNA-mutagenized population and is designated as flaky pollen (flk), since
the pollen grains lack the pollen coat, resulting in a defect of the pollen
recognition by the stigma. Under a high humidity condition, however, the
pollen grains can germinate and elongate pollen tubes into the stigmatic
papillae, suggesting the pollen grains are viable. The FLK gene encodes the
HMG-CoA synthase that is a single-copy gene in Arabidopsis. From Northern
and RT-PCR analyses, the gene is expressed at high levels in flower buds and
roots, and weakly expressed throughout the body. In anthers in the flower
buds, strong expression in the tapetum and relatively weak expression in the
microspores are observed by a promoter-GUS experiment and an in situ hybridization.
From a biochemical analysis, the flk pollen grains lack the sterols,
the major components of pollen coats. It is consistent with that the HMG-
CoA synthase is an essential enzyme in the mevalonate pathway required for
the sterol biosynthesis. In the flk tapetal cells, development of elaioplasts are
not observed. The elaioplasts present in the wild-type tapetum accumulate
granules designated plastoglobuli, that are mainly made from sterols. The
remnants of plastoglobuli are thought to be deposited on the surface of
maturing pollen grains after the tapetal cells are broken down. These results
indicate that the FLK gene is essential in tapetal cells for the biosynthesis of
sterols which then change into pollen coats.
In contrast with the above-described sporophytic defects of primarily
isolated flk alleles (flk-1 and flk-3) which have T-DNA insertions in the FLK
promoter region, recently identified null alleles of flk mutants (flk-4 and flk-5)
show a gametophytic male sterility, whereas no defects in the function of
female gametophyte. These observations suggest that the requirement of
FLK gene (i.e. the requirement of mevalonate pathway) is variable depending
on the cell types.
T01 Development 1 (Flower, Fertilization, Fruit, Seed)