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

357 Association Mapping of Shade Avoidance Responses in Arabidopsis thaliana
Daniele Filiault 1 , Carolyn Wessinger 1 , Keyan Zhao 2 , Magnus Nordborg 2 , Julin Maloof 1
1
University of California, Davis, 2 University of Southern California
Natural variation in developmental responses to light quality has been shown to have adaptive value. The goal of this
work is to assess the genetic basis of variation in phytochrome B mediated responses through association mapping using
both candidate gene and whole genome scan approaches. To this end, 95 Arabidopsis thaliana accessions were grown
under high and low red:far-red ratios to simulate shade and sun conditions. Plants were phenotyped for shade avoidance
and hypocotyl elongation responses. Regression analysis was then used to examine associations between these phenotypic
parameters and polymorphisms in loci known to play a part in phytochrome B responses, including eight polymorphisms
in phytochrome B itself. Variation in both shade avoidance and hypocotyl elongation phenotypes was observed among
the accessions and significant associations between this variation and a number of candidate gene polymorphisms were
found. These results suggest that variation in many different loci contributes to the observed phenotypic variation. A
genome-wide scan to identify potential novel loci involved in phytochrome B mediated responses was also performed
using a marker set spaced at about 50kb intervals throughout the genome.
358 Comparative Genomics of the Arabidopsis thaliana and Oryza sativa BTB Gene
Superfamilies.
Derek Gingerich 1 , Shin-Han Shiu 2 , Richard Vierstra 1
1
University of Wisconsin - Madison, 2 Michigan State University
Selective modification of proteins by ubiquitination is directed by diverse families of ubiquitin protein ligases (or
E3s). A large collection of E3s use Cullins (CULs) as scaffolds to form multisubunit E3 complexes in which the CUL
binds both a target recognition subcomplex and the RBX1 docking protein which delivers the activated ubiquitin moiety.
In one family, CUL3 proteins associate with RBX1 and members of the Broad Complex/Tramtrack/Bric-a-Brac (BTB)
protein family to form BTB E3s. Analysis of the BTB families in eukaryotes has shown that there is significant diversity
with respect to domain architecture between plants, nematodes, arthropods, and vertebrates, and, further, that there have
been independent expansions of subfamilies within different lineages. This suggests that evolution of E3 target-recognition
proteins may be closely tied to diversification of targets as lineages evolve.
We previously described a family of 80 BTB genes in Arabidopsis and showed that members of the family are able
to interact with AtCUL3a and AtCUL3b. Here we describe identification and analysis of the 150-member rice BTB
superfamily. Comparison of the two superfamilies shows they are very similar in domain architectures and subfamily
sizes, implying they regulate functions common to both monocots and eudicots. The primary difference occurs in the
MATH-BTB subfamily, where in rice there has been a dramatic expansion of the subfamily (77 members) compared to
Arabidopsis (6 members). Phylogenetic, gene structure, and expression analysis shows that 4 of the rice MATH-BTB loci
fall into a core group with the 6 Arabidopsis members, suggesting that these genes have functions conserved between
the two species. The remaining MATH-BTB genes in rice are significantly different, the majority sharing a single-exon
gene structure and most arranged in large tandem duplication blocks. In addition to the 150 functional BTB loci, we also
identified 41 putative BTB pseudogenes, 39 of which are in the MATH-BTB subfamily. The large expansion and high
number of pseudogenes in this subgroup suggests rapid birth and death evolution.