Epistasis underlying female sterility detected in hybrid breakdown in a Japonica?Indica cross of rice (Oryza sativa L.)

Abstract

Epistasis is considered to be a primary genetic basis of hybrid breakdown. We found novel epistatic genes causing hybrid breakdown in an intraspecific cross of cultivated rice (Oryza sativa L.). F2 progeny derived from a cross between a Japonica variety, Asominori, and an Indica variety, IR24, showed segregation of high sterility for seeds, even though the reciprocal F1 hybrids showed about 60% seed fertility. Backcross populations (BC3F2, BC3F3), obtained from repeated backcrossing with Asominori, showed the segregation of causal genes in a simple Mendelian fashion. Using these populations, we identified that this sterility was hybrid breakdown caused by interaction among three nuclear genes distributed on the both parental genomes. These new genes, designated as hsa1, hsa2, and hsa3, were found to be involved in female gamete development by histological examination. The Indica parent IR24 has a sterile allele, hsa1-IR, which was located at near RFLP marker G148 on chromosome 12, whereas the Japonica parent Asominori has two sterile alleles, hsa2-As on chromosome 8 (close to G104) and hsa3-As on chromosome 9 (close to RM285). Female gametes carrying the hsa1-IR, hsa2-As, and hsa3-As alleles aborted in hsa1-IR homozygous plant, leading to seed sterility and selective elimination of the specific allelic combination. This study provides direct evidence that hybrid breakdown is attributed to epistatic interaction of genes from both parents and suggests that complicated mechanisms has been developed for hybrid breakdown during the evolution of rice.

A Simple Genetic Incompatibility Causes Hybrid Male Sterility in Mimulus

“…In this system, Kubo and Yoshimura (2002) have genetically mapped both partners of a two-locus incompatibility with major effects on hybrid viability and fertility. Recently, the same authors mapped a different three-locus genetic incompatibility that exclusively affects hybrid female fertility (Kubo and Yoshimura 2005). The genetic basis of hybrid male sterility between species of Oryza also appears simple: a major sterility factor from O. glaberrimo causes male gamete abortion against an O. sativa genetic background (Sano 1990).…”

“…Interestingly, a study of hybrid incompatibilities between Lycopersicon species identified several QTL that affect both male and female fertility, which could be due to pleiotropic effects of individual Dobzhansky-Muller interactions (Moyle and Graham 2005). Furthermore, a two-locus genetic incompatibility causes male and female sterility between the Indica and Japonica varieties of O. sativa (Kubo and Yoshimura 2005).…”

“…In plants, for example, dominant hybrid incompatibility alleles are not uncommon (e.g., 1 Hollingshead 1930; Stephens1946; Macnair and Christie 1983;Christie and Macnair 1984;Kubo and Yoshimura 2005; but see Moyle and Graham 2005). In addition, the genetic complexity that typifies Drosophila hybrid male sterility is not necessarily mirrored in other systems.…”

“…In addition, the genetic complexity that typifies Drosophila hybrid male sterility is not necessarily mirrored in other systems. Remarkably, hybrid sterility between varieties of cultivated rice, Oryza sativa, is often genetically simple (Oka 1974;Liu et al 1997;Kubo and Yoshimura 2002;Kubo and Yoshimura 2005). It also is not clear that hybrid male sterility should always evolve more readily than female sterility or lethality.…”

Molecular cytogenetics and DNA sequence analysis of an apomixis-linked BAC in Paspalum simplex reveal a non pericentromere location and partial microcolinearity with rice

“…On the other hand, several independent studies located loci responsible for spikelet sterility in the same area of chromosome 12 that was homologous to the ACL of P. simplex (Wu et al 1995;Wan et al 1996;Liu et al 2001). More recently Kubo and Yoshimura (2004) mapped in the same area the locus hsa1 responsible for hybrid breakdown in indica/japonica crosses. In all these cases the spikelet sterility was related to defective development of the embryo sac.…”