Genetics of sterility in hybrids between wild and cultivated ...
Genetics of sterility in hybrids between wild and cultivated rice strains Division seminar 24/ Sep/ 08 Yohei Koide
Introduction Topics 1 Hybrid sterility between Oryza sativa and O. glaberrima Topics 2 Hybrid sterility within Asian rice species
What is Hybrid sterility?? Equus caballus Horse Equus asinus x Equus caballus x Sterile… Mule Equus asinus Donkey
What is Hybrid sterility?? O. glaberrima O. sativa F1 Hybrid
Hybrid vigor Genetic divergence Inbreeding depression Hybrid inviability Hybrid sterility Heterosis Barrier between species Reproductive barrier Fig. General pattern of vigor in hybrids and genetic divergence between the parents. Race Within Species Different species
Fertilization Reproductive phase Vegetative phase F1 F2 Cross incompatibility (Pre- and Post zygotic) Hybrid inviability Hybrid sterility Fig. Reproductive barriers in plant hybrids.
Table number of reproductive isolation related-genes reported in plants reviewed by Koide et al . 2008a In Oryza , there are many hybrid sterility genes reported. Hybrid sterility is important in Oryza (?)
reviewed by Koide et al . 2008a One locus gametophytic hybrid sterility genes have been frequently observed in Oryza .
What is ‘one locus gametophytic hybrid sterility gene’?? S / S S a / S a Strain A Strain B x S / S a Hybrid Pollen Embryo sac S S S a S a S/S S a /S a S/S a S/S a S a /S a S/S a S/S 1 2 1
What is ‘one locus gametophytic hybrid sterility gene’?? S / S S a / S a Strain A Strain B x S / S a Hybrid S S S a S a Pollen Embryo sac S a /S a S/S a S/S 1 2 1 S/S S a /S a S/S a S/S a Segregation distortion Selfish!! Semi-sterile Semi-sterile
Segregation distortion After Harushima et al . 2002 Segregation distortion may prevent the introgression of useful genes.
What is the importance of studying hybrid sterility?? 1. for breeding 1-1. Sterility decreases yield. 1-2. Hybrid sterility genes prevent the introgression of useful genes. 2. for studying evolution Hybrid sterility is one of the mechanisms of reproductive barrier between species. We can answer the question of ‘What is the species?’
Topics 1 Hybrid sterility between Oryza sativa and O. glaberrima Topics 2 Hybrid sterility within Asian rice genepool Hybrid sterility gene, S1 Hybrid sterility gene, S6
S1 S1 a S1/S1 a O. glaberrima T65 S1 (W025BC) O. sativa T65 wx Wx OsC1 Hd1 R111 R32 RM3140 Chromosome 6 S 1 Hybrid sterility between Oryza sativa and O. glaberrima S1 a S1 S1 S1 a S1/S1 ♀ ♂
Pollen semi-sterility Normal embryo sac Abnormal embryo sac Cytological observation of F1 hybrids What is the causative gene? Wx pollen wx pollen S1 a S1 Wx wx
Pollen fertility QTL and segregation distortion detected by Doi et al . 1998. Is this gene common in hybrids between Asian and African rice? OSR19( Waxy )***** OSR25***** RM204***** G039***** RM253***** C Se-1 RM3a RM30 G342 Chromosome 6 Linkage map constructed by Lorieux et al . 2000
Hybrid sterility between Oryza sativa and O. glaberrima Topics 1 1. What gene(s) are involving in this phenomenon? 2. How does it distribute in Asian and African rice strains? Fine mapping Test crossing
Koide et al . 2008b Fig. Fine mapping of S1 locus
Os06g0141400 Os06g0141600 Os06g0141700 Os06g0141800 Os06g0142000 Os06g0142100 Os06g0142200 Os06g0142300 Similar to early nodulin Early nodulin 93 Similar to early nodulin Similar to Ribosome biogenesis regulatory protein homolog Conserved hypothetical protein Cyclin-like F-box domain containing protein Early nodulin Early nodulin 93 Locus name Function Table Predicted ORFs in candidate region of S1 locus
M M M M S S S a + + + ? ? ? x x Tester line A Tester line B Unknown genotype S a Test crosses to determine the distribution of the S1 gene. Normal Distortion high low Normal high Distortion low Fertility ?= S a ?= S Fertility Segregation Segregation
O. sativa - O. rufipogon complex O. glaberrima O. barthii Allelic distribution of the S1 locus Tester line with S1 Tester line with S1 a Low Distortion Low Distortion S1 a S1
Hybrid sterility between Oryza sativa and O. glaberrima Topics 1 1. What gene(s) are involving in this phenomenon? 2. How does it distribute in Asian and African rice strains? S1 locus was delimited to a 40kb region. There were four repeated early nodulin genes, a ribosome biogenesis regulatory protein homolog, and unknown ORFs. The allelic states of the S1 locus was clearly diverged between Asian and African rice species. S1 gene is one of the candidate speciation genes between Asian and African rice species.
Frequencies of genotype S 6 T65 wx homozygote W593 homozygote T65 wx ×W593A F 2 99 plants Wx OsC1 Hd1 R111 R32 RM3140 Chromosome 6 100% 50% 25% 0% 75% heterozygote Segregation distortion Fig. S6 genetic model O. sativa T65 wx O. rufipogon W593A (NIL) Topics 2 Hybrid sterility within Asian rice species Fig. Segregation distortion detected in the F2 population derived from the cross between T65 wx and W593A.
S6 fine mapping Due to the deficit of recombination near the centromere, the S6 locus was delimited to a region of more than 8Mb, even with a large mapping population. 8Mb!!
S6 S6 a S6 a Allelic distribution of the S6 locus Neutral allele, S6 n Neutral allele, S6 n Koide et al. 2008c S6 n S6 n
S6 n was located in the region where S6 was located Fine mapping of the S6 n allele by using an indica strain, Patpaku, which suggested to contain S6 n allele.
Is there association between genetic diversity and allelic state of the S6 locus? Genetic association This locus has same genetic history as mutation locus This locus has different genetic history as mutation locus because of the recombination Even the locus is near the mutation, it doesn’t have same genetic history as mutation locus Thus, association between phenotype and marker genotype is 1. strong if marker is near the mutation. 2. strong if mutation appeared recently.
A B Genetic diversity A B Individuals with phenotype Individuals without phenotype
The relative ratio of the genetic diversity of the strains with S6 to the strains with S6 n Decreasing near the centromere
Genetic diversities of S6 S6 a and S6 n The genetic diversities of S6 and S6 a were decreased at specific chromosomal region. The causative alleles might locate near the locus. The genetic diversity of S6 n was not decreased . S6 n has longer history than S6 and S6 a .
Topics 2 Hybrid sterility within Asian rice species There were three alleles at the S6 locus. S6 n were distributed widely in O. sativa and O. rufipogon . A prominent reduction in the genetic diversity of S6 and S6 a was detected. Hybrid sterility gene, S6 Association mapping is potentially useful in this region. S6 and S6 a are newly arisen allele. S6 and S6 a were found in limited geographic area. S6 and S6 a were originated independently (from S6 n ??). S6 S6 a S6 n S x S a = incompatible Selfish genes evolved without selective advantages???