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

365 Exploring the Evolution of Tandemly Duplicated Receptor Like Kinases in Arabidopsis
Adriana Racolta 2, 1 , Frans Tax 1
1
Department of Molecular and Cellular Biology, 2 IGERT Program in Genomics, University of Arizona
Almost one in five Arabidopsis genes is found next to their most close relative. Among receptor-like kinases (RLKs)
genes, 33% are organized in tandem duplications or larger clusters. We are interested in understanding why tandem
duplicated genes are maintained in the genome. Gene fate after duplication can include inactivation, neo-functionalization
and sub-functionalization. We chose to compare DNA sequences from a pair of tandem genes, At2g13790 and At2g13800,
which are related to the leucine rich repeat (LLR)-RLK BAK1 which participates in steroid signal transduction. Sequence
evolution of these two paralogous genes was analyzed in Col ecotype using the Ka/Ks ratio for each protein domain.
The low rate of nucleotide substitution in the kinase domain in both coding and non-coding regions indicates that gene
conversion is probably maintaining the high identity. Stabilizing selection appears to maintain similarities in the LRR
domain of the two genes. For a more complete comparison we also sequenced the kinase domain of the two paralogs in
the distantly related ecotype Cvi-0 and compared them with the Col sequences as a measure of their divergence. This
leads to the finding that within each ecotype the two genes are more closely related to each other than with the gene pair
in the other ecotype. A more recent substitution event, R420L in the highly conserved kinase domain of Col At2g13800
was not detected in Cvi-0 indicative of possible inactivation of this gene in Col ecotype. Complete sequencing of both
genes in Cvi-0 will allow for a more complete analysis.
366 Wide Variation in Geminivirus-Mediated VIGS of ChlI in Arabidopsis Ecotypes
Miguel Flores-Vergara 2 , John Tuttle 2 , Susanne Kjemtrup 1 , Dominique Robertson 2
1
Paradigm Genetics, RTP, NC, US, 2 North Carolina State University, Raleigh, NC US
The geminivirus cabbage leaf curl virus (CaLCuV) has been modified to serve as a transient gene silencing vector for
Arabidopsis. In a screening of over 100 different Arabidopsis accessions, extensive variation in the degree of silencing
of an endogenous gene (ChlI), needed for chlorophyll formation, was seen. A total of 20 plants from each ecotype was
bombarded with the VIGS vector, and the experiment was repeated once. Wile some ecotypes lacked detectable silencing,
others showed extensive ChlI silencing. Viral symptoms also varied from minimal to severe, and the two traits were
not correlated. The responses were grouped into four general classes, with the most abundant class showing symptoms
(stunted growth and leaf curling) and ChlI silencing, and the next most abundant class showing symptoms but no visible
ChlI silencing. Several ecotypes showed extensive silencing with minimal symptoms and could be suitable as a host for
virus-induced gene silencing. One class lacked both symptoms and silencing and is a possible candidate for a geminivirus
resistance gene. In addition to the four general classes of response, two ecotypes were identified that consistently lost
ChlI silencing in new growth. Although the screen was performed at 22/20 o , short day conditions, four ecotypes with mild
symptoms and extensive ChlI silencing were also compared for VIGS response at different temperatures. ChlI silencing
was generally greater at 25/23 o , but Kil-0 retained extensive ChlI silencing at 16/14 o while Le-0 did not and there was
minimal effect on symptoms for the four ecotypes. Because the wide variation in response to CaLCuV:ChlI infection
occurred in ecologically fit accessions, this system provides a unique opportunity to identify genetic components that
mediate epigenetic responses to a DNA virus, and to VIGS of an endogenous gene mediated by that virus.
1. S. Kjemtrup's current address: Monsanto-RTP, Research Triangle Park, NC US
2. Supported by NSF STTR 021503 to SK and DR