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SUMMARY:Between a rock and a hard place - resistance evolution and genetic
  incompatibility in plants. - Kirsten Bomblies\, Department of Organismic 
 and Evolutionary Biology\, Harvard University
DTSTART:20091015T150000Z
DTEND:20091015T160000Z
UID:TALK20031@talks.cam.ac.uk
CONTACT:Ian Henderson
DESCRIPTION:Understanding early causes and consequences of genetic diverge
 nce is important for elucidating how intrinsic gene flow barriers might ar
 ise among populations during speciation. Arabidopsis thaliana is a primari
 ly self-fertilizing plant species made up of many essentially independentl
 y diverging lineages with little gene flow among them\, making it an ideal
  model system for investigating early stages of genetic divergence. We exa
 mined progeny of 1487 intercrosses among 311 wild accessions. Most were co
 mpatible\, as expected for within-species crosses\, but 21 first-generatio
 n hybrids showed strongly deleterious phenotypes including dwarfism\, seve
 re tissue necrosis and sterility. In independent cases we found that this 
 is due to hyperactivation of the plant immune system (effectively\, plant 
 autoimmunity). Consistent with this\, at least two cases are caused by com
 binations of different known or suspected pathogen resistance ( R ) genes.
  Plant immune systems\, like animal immune systems\, are necessarily diver
 se to counter the barrage of variable pathogens that attempt to exploit th
 em. However\, for all their benefits\, plant pathogen resistance genes are
  inherently dangerous entities that regulate a terminal programmed cell de
 ath response. Genetic divergence among immune system genes can thus have d
 ire consequences for hybrid progeny in crosses among plant lineages where 
 protein partners have not co-evolved to function together. Our results\, t
 ogether with results from other groups\, suggest that pathogen pressure ma
 y indirectly promote genetic incompatibility by promoting divergence of R 
 genes. Furthermore\, the prevalence of such "hybrid necrosis" phenotypes s
 uggests that 1) A. thaliana is a useful model for understanding a common p
 henomenon in plants\, and 2) that necrosis may be an important factor in t
 he adaptive evolution of the plant immune system. 
LOCATION:Department of Plant Sciences\, Large Lecture Theatre
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