75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

415 The F-box Protein PPS Functions as a Positive Regulator of Light Signaling in Arabidopsis
Hui Shen, Phi Luong, Enamul Huq
Section of Molecular Cell and Developmental Biology and The Institute for Cellular and Molecular Biology,
The University of Texas at Austin, Austin, TX 78712
Because light is vital for plants development, they are equipped with an array of photoreceptors that respond to
different wavelengths of ambient light spectrum. Phytochromes (phys) and cryptochromes (crys) are the photoreceptors
that respond to red (R), far-red (FR) and blue (B) regions of the spectrum by unknown mechanisms. Genetic approaches
have identified both positive and negatively acting components in these light-signaling pathways; however, none of
these pathways seem to be saturated. In an effort to identify additional components, we have screened available T-DNA
insertional lines under continuous R light and identified a new mutant named pleiotropic photosignaling, pps. pps showed
longer hypocotyls and smaller cotyledons under continuous R, FR and B light compared to that of the wild type. However,
the long hypocotyl phenotype of pps is much stronger under R compared to FR and B. When grown in continuous white
light, pps showed longer petiole length, higher number of inflorescence, shorter stature, and rounder leaves compared
to that of the wild type. pps mutants are much smaller in stature and leaves of pps are much less expanded compared to
that of the WT in short day (SD) conditions. Cloning of PPS using a combination of map-based cloning and candidate
gene approach showed that it encodes MAX2/ORE9, an F box protein previously shown to be involved in inflorescence
architecture and senescence. Since PPS is predicted to be a component of SCF complex involved in regulated proteolysis,
these results suggest that SCF PPS complex plays critical roles downstream of all light signaling pathways. In addition,
these results also suggest that PPS may regulate multiple targets at different developmental stages to optimize plant
growth and development.
416 Functional Analysis of the SAUR Family of Auxin-Inducible Genes
Angela Spartz 1 , Star Weivoda 1 , Hironori Ito 1 , Paul Overvoorde 2 , William Gray 1
1
University of MInnesota, St. Paul, MN, 2 Macalester College, St. Paul, MN
SAUR (Small Auxin Upregulated RNAs) genes were first identified nearly 20 years ago as primary auxin response
genes. Arabidopsis contains at least 77 SAUR genes, which are predicted to encode low molecular weight proteins of
10-15kD. Sequence analysis of the SAUR proteins provides few clues as to their function, and what role if any they play
in the auxin response pathway remains to be established. To investigate the functional importance of the SAUR genes,
we have focused on a small subfamily containing SAURs 19-29, which share 73-95% identity at the amino acid level.
Promoter-GUS reporter analysis has revealed overlapping, yet distinct, expression patterns. Notably, all of the promoter
constructs tested are auxin inducible and exhibit strong expression in elongating cells of the hypocotyl. The large number
of highly related SAUR genes suggests considerable functional redundancy in this gene family, complicating loss-offunction
genetic studies. Therefore, we have taken an overexpression-based approach. Wild-type plants expressing a
35S:GFP-SAUR19 transgene exhibit several auxin-related phenotypes, including slight auxin-resistant root elongation,
increased lateral and adventitious root development, elongated hypocotyls, and wavy root growth. Additionally, etiolated
seedlings lack apical hooks and display increased root gravitropism and decreased hypocotyl phototropism. While these
phenotypes are also observed with 35S:SAUR19 fusion proteins containing other N-terminal tags, plants expressing
untagged SAUR19 appear completely normal. Preliminary immunoblot studies with a polyclonal SAUR19 antibody
suggest that the N-terminal GFP tag stabilizes SAUR19, facilitating overexpression. We cannot however, rule out the
possibility that the GFP-SAUR19 fusion protein acts in a dominant-negative manner. Nonetheless, these findings provide
strong genetic support for the hypothesis that SAUR proteins play an important role in auxin response. We are seeking to
elucidate the molecular basis for these phenotypes by identifying SAUR19 interacting proteins and through microarray
analysis of our transgenic lines.