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

359 eQTL-mapping reveals AMP2A, a circadian regulated dioxygenase affecting rhythmic leaf
movement
Samuel Hazen 1 , Tatjana Singer 2 , Yiping Fan 3 , Steven Briggs 4 , Steve Kay 1
1
The Scripps Research Institute, 2 The Salk Institute, 3 St. Jude Children's Research Hospital, 4 University of
California, San Diego
Organisms have evolved to coordinate their activities with the day-night cycle caused by the Earth's rotation with an
internal mechanism known as the circadian clock. Anticipating environmental changes rather than simply reacting to them
increases photosynthesis, growth, and survival. Arabidopsis accessions often exhibit diverse circadian properties that are
under genetic control. We combined high-density array genotyping and transcription profiling the Col/Ler recombinant
inbred line population to explore this natural variation and identified an eQTL associated with leaf movement rhythms.
The expression of a putative dioxygenase located in a previously mapped QTL was strongly correlated with the amplitude
of leaf rhythms. We discovered that the Col allele of the putative causal gene is rhythmically expressed while the Ler
allele, which has a positive effect on amplitude, is not expressed at all. The expression polymorphism occurs in at least
one third of all accessions tested and is likely caused by a 23bp deletion in the upstream regulatory region. Moreover, a
loss-of-function mutant in Col exhibited increased amplitude and thus confirmed the phenotype association. Flowering
time and the expression of several core clock genes are not altered in the loss-of-function mutant; therefore, the putative
dioxygenase appears to be part of circadian regulated output pathway.
360 Arabidopsis/oomycete symbioses provide a model for phylogenomics and molecular
epidemiology in plants
Eric Holub
University of Warwick
Much progress has been made from molecular genetics of disease resistance, with Arabidopsis thaliana pathology at
the forefront in revealing parallels with innate immunity of animals. Since coevolution emerged as a research topic more
than 25 years ago, there has been general agreement that disease resistance evolves within plant species by a treadmill of
balancing selection involving parasite recognition proteins encoded by R-genes and matching “avirulence” effectors (AVR
genes) in the parasite (1). Evidence for an adaptive “arms race” driving speciation of the host as well as the parasite has
yet to be revealed. This may begin to change with phylogenetic analyses of host genes that govern basic compatibility in
plant-parasite symbioses, or that delimit host specialization of parasite taxa. Ellingboe (2) defined basic compatibility as
an evolved state that exists between taxa (species or subspecies) of a plant and a parasite that has adapted to survive and
proliferate in that host. The adapted parasite must be equipped to evade or overcome constitutive barriers and inducible
defenses of its compatible host, and possess the developmental and metabolic characteristics necessary to exploit its nutritious
environment. He suggested that the evolution of R-AVR mediated resistance is superimposed onto basic compatibility.
The parasite secretome of effector-like genes and any known corresponding host R-genes will provide a focus for future
research. Genome-wide comparative biology among species of hosts and parasites would constitute phylogenomics of
parasitic symbioses, whereas variability within species would enable microevolutionary or molecular epidemiology. Research
of Arabidopsis associations with its adapted oomycete parasites (Hyaloperonospora parasitica and Albugo candida) will
provide pull-through knowledge into crops and other wild plant species (1). Exciting progress has recently been made in
molecular characterisation of effector proteins from H. parasitica, based on recognition by corresponding Arabidopsis R-
genes. A large number of effector-like proteins may be gleaned and classified by bioinformatics from a reference genome
of H. parasitica (isolate HpEmoy2) and developed for different experimental uses in comparative biology. Some may prove
useful for phylogenomics among species, and others may prove most useful for molecular epidemiology.
1 Holub, EB. Curr. Opin. Plant Biol. 2006 in press.
2 Ellingboe, AH. In Physiological Plant Pathology (Encycl. of Plant Physiol., Vol 4). Heitefuss R, Williams, PH (eds): Springer. 1976:761-778.