Katsuyuki Ichitani

Phylogenetic analysis of the rDNA intergenic spacer subrepeats and its implication for the domestication history of foxtail millet, Setaria italica

We sequenced ribosomal DNA intergenic spacer subrepeats and their flanking regions of foxtail millet landraces from various regions in Europe and Asia and its wild ancestor to elucidate phylogenetic differentiation within each of types I–III found in our previous work and to elucidate relationships among these three types. Type I was classified into seven subtypes designated as Ia–Ig based on subrepeat sequences; C repeats downstream of those subrepeats are also polymorphic. Of these, subtypes Ia–Id and Ig were found in foxtail millet landraces. Subtypes Ia and Ib were distributed broadly throughout Asia and Europe. Subtype Ic was distributed in China, Korea and Japan. Subtype Id has a 20-bp deletion in subrepeat 3 and has a unique C repeat sequence. This subtype was found in a morphologically primitive landrace group from Afghanistan and northwestern Pakistan and differed greatly from other type I subtypes, implying that these landraces were domesticated independently. Subtypes Ig was found in a landrace from Pakistan and Ia and Ie–Ig were in six wild ancestor accessions. Type II was also highly polymorphic and four subtypes were found and designated as subtypes IIa–IId, but sequence analyses indicated type III as monomorphic. The present work indicates that type III should be classified as a subtype of type II (subtype IIe). Sequence polymorphism of subrepeats of types I–III indicated that subrepeats of subtype IIa are greatly divergent from others. Relationships among types I–III are much more complicated than anticipated based on previous RFLP work.

Molecular relationships between Australian annual wild rice, Oryza meridionalis, and two related perennial forms

BackgroundThe perennial, Oryza rufipogon distributed from Asia to Australia and the annual O. meridionalis indigenous to Australia are AA genome species in the Oryza. However, recent research has demonstrated that the Australian AA genome perennial populations have maternal genomes more closely related to those of O. meridionalis than to those found in Asian populations of O. rufipogon suggesting that the Australian perennials may represent a new distinct gene pool for rice.ResultsAnalysis of an Oryza core collection covering AA genome species from Asia to Oceania revealed that some Oceania perennials had organellar genomes closely related to that of O meridionalis (meridionalis-type). O. rufipogon accessions from New Guinea carried either the meridionalis-type or rufirpogon-type (like O. rufipogon) organellar genomes. Australian perennials carried only the meridionalis-type organellar genomes when accompanied by the rufipogon-type nuclear genome. New accessions were collected to better characterize the Australian perennials, and their life histories (annual or perennial) were confirmed by field observations. All of the material collected carried only meridionalis-type organellar genomes. However, there were two distinct perennial groups. One of them carried an rufipogon-type nuclear genome similar to the Australian O. rufipogon in the core collection and the other carried an meridionalis-type nuclear genome not represented in the existing collection. Morphologically the rufipogon-type shared similarity with Asian O. rufipogon. The meridionalis-type showed some similarities to O. meridionalis such as the short anthers usually characteristic of annual populations. However, the meridionalis-type perennial was readily distinguished from O. meridionalis by the presence of a larger lemma and higher number of spikelets.ConclusionAnalysis of current accessions clearly indicated that there are two distinct types of Australian perennials. Both of them differed genetically from Asian O. rufipogon. One lineage is closely related to O. meridionalis and another to Asian O. rufipogon. The first was presumed to have evolved by divergence from O. meridionalis becoming differentiated as a perennial species in Australia indicating that it represents a new gene pool. The second, apparently derived from Asian O. rufipogon, possibly arrived in Australia later.

Chromosomal Location of HWA1 and HWA2, Complementary Hybrid Weakness Genes in Rice

Hybrid weakness phenomena in rice reportedly have two causes: those of HWC1 and HWC2 genes and those of HWA1 and HWA2 genes. No detailed study of the latter has been reported. For this study, we first produced crosses among cultivars carrying the weakness-causing allele on the HWA1 and HWA2 loci to confirm the phenotype of the hybrid weakness and the genotypes of the cultivars on the two loci, as reported earlier. We then confirmed that these cultivars belong to Indica. Subsequent linkage analysis of HWA1 and HWA2 genes conducted using DNA markers revealed that both genes are located in the 1,637-kb region, surrounded by the same DNA markers on the long arm of chromosome 11. The possibility of allelic interaction inducing hybrid weakness is discussed.

Geographical variation of foxtail millet, Setaria italica (L.) P. Beauv. based on rDNA PCR–RFLP

The rDNA PCR–RFLP of foxtail millet (Setaria italica) germ-plasm collected throughout Eurasia and from a part of Africa was investigated with five restriction enzymes according to our previous study. Foxtail millet germ-plasms were classified by length of the rDNA IGS and RFLP; clear geographical differentiation was observed between East Asia, the Nansei Islands of Japan-Taiwan-the Philippines area, South Asia and Afghanistan-Pakistan. We also found evidence of migration of foxtail millet landraces between the areas. We calculated diversity index (D) for each region and found that center of diversity of this millet is East Asia such as China, Korea and Japan.

Interactive effects of two heading-time loci, Se1 and Ef1, on pre-flowering developmental phases in rice (Oryza sativa L.)

The interaction between the Se1 and the Ef1 loci, which chiefly control the photoperiod sensitivity (PS) and the basic vegetative growth (BVG) period of rice (Oryza sativa L.) respectively, was investigated using four tester lines different in genotype for the two heading time loci from each other. The four tester lines were grown under 10, 13, 14, 15, and16h day lengths to estimate their BVG period and PS. The Taiwanese cultivar Taichung 65(T65), one of the tester lines, has an extremely long BVG period that has been considered to be conferred by a late heading-time allele ef1 at the Ef1 locus. Experimental results, however, showed that the extremely long BVG of T65was conferred not by a single effect ofef1 but by a complementary effect ofef1 and Se1-e, a photoperiod insensitivity allele, at theSe1 locus. It was also found that a complementary effect of a PS allele Se1-n at the Se1 locus and ef1stimulates the PS of rice. Gene analysis for heading time under an optimum daylength (10 h) as well as under natural day length confirmed the presence of the complementary effect of the two nonallelic genes on BVG, which was found only with homozygosity of both the genes. Based on these results and earlier reports on the Se1 locus, the roles of the Se1 andEf1 loci on the durations of pre-flowering developmental phases in rice were discussed.

rDNA polymorphism of foxtail millet (Setaria italica ssp. italica) landraces in northern Pakistan and Afghanistan and in its wild ancestor (S. italica ssp. viridis)

Ribosomal DNA (rDNA) spacer length polymorphism was studied in foxtail millet (Setaria italica ssp. italica) landraces from Pakistan and Afghanistan and in its wild ancestor (S. italica ssp. viridis) from Pakistan by PCR-based methods. Sequence polymorphism was also investigated for accessions selected based on the observed length polymorphism. The PCR-based length polymorphism and sequence polymorphism of rDNA intergenic spacer (IGS) clearly demonstrated genetic differentiation between cultivated and wild forms in the region. Genetic differentiation was observed between different areas to some extent in the cultivated form, and between different regions in the wild form of northern Pakistan. Based on the results, we discuss the genetic differentiation of foxtail millet and wild ancestor in this region and possible utility of rDNA markers to trace the dispersal of this crop in the region.

Identification and linkage analysis of a new rice bacterial blight resistance gene from XM14, a mutant line from IR24

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is a chief factor limiting rice productivity worldwide. XM14, a rice mutant line resistant to Xoo, has been obtained by treating IR24, which is susceptible to six Philippine Xoo races and six Japanese Xoo races, with N-methyl-N-nitrosourea. XM14 showed resistance to six Japanese Xoo races. The F2 population from XM14 × IR24 clearly showed 1 resistant : 3 susceptible segregation, suggesting control of resistance by a recessive gene. The approximate chromosomal location of the resistance gene was determined using 10 plants with shortest lesion length in the F2 population from XM14 × Koshihikari, which is susceptible to Japanese Xoo races. DNA marker-assisted analysis revealed that the gene was located on chromosome 3. IAS16 line carries IR24 genetic background with a Japonica cultivar Asominori segment of chromosome 3, on which the resistance gene locus was thought to be located. The F2 population from IAS16 × XM14 showed a discrete distribution. Linkage analysis indicated that the gene is located around the centromeric region. The resistance gene in XM14 was a new gene, named XA42. This gene is expected to be useful for resistance breeding programs and for genetic analysis of Xoo resistance.

Chromosomal Location of HCA1 and HCA2, Hybrid Chlorosis Genes in Rice

Many postzygotic reproductive barrier forms have been reported in plants: hybrid weakness, hybrid necrosis, and hybrid chlorosis. In this study, linkage analysis of the genes causing hybrid chlorosis in F2 generation in rice, HCA1 and HCA2, was performed. HCA1 and HCA2 are located respectively on the distal regions of the short arms of chromosomes 12 and 11. These regions are known to be highly conserved as a duplicated chromosomal segment. The molecular mechanism causing F2 chlorosis deduced from the location of the two genes was discussed. The possibility of the introgression of the chromosomal segments encompassing HCA1 and/or HCA2 was also discussed from the viewpoint of Indica-Japonica differentiation.

Geographic distribution of Waxy gene SNPs and indels in foxtail millet, Setaria italica (L.) P. Beauv.

To elucidate diversity and evolution of the Waxy gene in foxtail millet, Setaria italica, we analyzed sequence polymorphism of Waxy gene in 83 foxtail millet landraces collected from various regions covering the entire geographical distribution of this millet in Europe and Asia. We found a unique geographic distribution pattern at the sequence level of gene haplotypes and also found a large diversity in East Asian landraces. We also found a higher degree of genetic polymorphism in a non-waxy phenotype than in other low amylose types, supporting the hypothesis that low amylose types recently originated from non-waxy type.

Genetic analysis of ion-beam induced extremely late heading mutants in rice.

Two extremely late heading mutants were induced by ion beam irradiation in rice cultivar ‘Taichung 65’: KGM26 and KGM27. The F2 populations from the cross between the two mutants and Taichung 65 showed clear 3 early: 1 late segregation, suggesting control of late heading by a recessive gene. The genes identified in KGM26 and KGM27 were respectively designated as FLT1 and FLT2. The two genes were mapped using the crosses between the two mutants and an Indica cultivar ‘Kasalath’. FLT1 was located on the distal end of the short arm of chromosome 8. FLT2 was located around the centromere of chromosome 9. FLT1 might share the same locus as EHD3 because their chromosomal location is overlapping. FLT2 is inferred to be a new gene because no gene with a comparable effect to that of this gene was mapped near the centromere of chromosome 9. In crosses with Kasalath, homozygotes of late heading mutant genes showed a large variation of days to heading, suggesting that other genes affected late heading mutant genes.