Poster: Reproductive Development

Abs # 461: The expression of SP11 determines the linear dominance relationship among four class-II S haplotypes on the pollen side in Brassica self-incompatibility

Presenter:	Watanabe, Masao , nabe@iwate-u.ac.jp
Authors	Watanabe, Masao  (A)   Kakizaki, Tomohiro  (A)   Takada, Yoshinobu  (A)   Ito, Akiko  (A) (D)  Suzuki, Go  (B)   Shiba, Hiroshi  (C)   Takayama, Seiji  (C)   Isogai, Akira  (A)
Affiliations:	(A): Faculty of Agriculture, Iwate University (B): Division of Natural Science, Osaka Kyoiku University (C): Graduate School of Biological Sciences, Nara Institute of Science and Technology (D): Iwate Biotechnology Research Center

Self-incompatibility (SI) systems prevent self-fertilization and promote out-crossing by rejecting pollen from plants with the same S haplotype. The Brassica SI system is controlled sporophytically by multiple alleles at the single locus, termed S locus. Because of sporophytic control of Brassica SI, dominance relationships among S haplotypes are observed in both stigma and pollen. We have previously identified five different class-II S haplotypes in Brassica rapa (syn. campestris). Here, we performed test-crosses between S heterozygotes and their respective parental S homozygotes for four of these class-II S haplotypes, and observed a linear dominance relationship on the pollen side. In order to determine how this dominance relationship is controlled, RNA gel blot analyses were performed for six S heterozygotes and their respective parental S homozygotes by using the corresponding SP11 cDNA clone as a probe. In all six S heterozygotes, SP11 derived from a dominant S haplotype was predominantly expressed, and SP11 derived from a recessive S haplotype was repressed. Therefore, the linear dominance relationship of the SI phenotype on the pollen side is regulated by the expression of SP11 gene.