Epigenetics Mechanisms for Breakdown of Self-Incompatibility in Inter-specific Hybrids
June B Nasrallah 1*, Pei Liu 1, Susan Sherman-Broyles 1, Renate Schmidt 2 and Mikhail E Nasrallah 1
1 Cornell University
2 Max-Planck-Institute, Golm
* To whom correspondence should be addressed. E-mail: jbn2{at}cornell.edu.
Submitted on December 9, 2006
Revised on January 11, 2007
Accepted on 13 January 2007
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Abstract |
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As a major agent of rapid speciation, inter-specific hybridization has played an important role in plant evolution. When hybridization involves species that exhibit self-incompatibility (SI), this pre-zygotic barrier to self-fertilization must be overcome or lost to allow selfing. How SI, a normally dominant trait, is lost in nascent hybrids is not known, however. Here we demonstrate that hybrid self-fertility can result from epigenetic changes in expression of the S-locus genes that determine specificity in the SI response. We analyzed loss of SI in synthetic hybrids produced by crossing self-fertile and self-incompatible species in each of two crucifer genera. We show that SI is lost in the stigmas of A. thaliana-lyrata hybrids and their neo-allotetraploid derivatives, and in the pollen of C. rubella-grandiflora hybrids and their homoploid progenies. Aberrant processing of S-locus receptor kinase gene transcripts as detected in Arabidopsis hybrids and suppression of the S-locus cysteine-rich protein gene as observed in Capsella hybrids are two reversible mechanisms by which SI might break down upon inter-specific hybridization to generate self-fertile hybrids in nature.
Key Words:
Brassicaceae, epigenetic mechanisms, inter-specific hybrids, self-fertiliy, self-incompatibility
