Development of an STS Marker Linked to Powdery Mildew Resistance Genes PmLK906 and Pm4a by Gene Chip Hybridization

Wheat （Triticum aestivum L.） line Lankao 90（6） carries a recessive powdery mildew resistance gene temporarily named PmLK906 on chromosome 2AL. Near PmLK906 there is another known powdery mildew resistance gene locus Pm4. To track the two powdery mildew resistance genes in wheat breeding program by marker assisted selection （MAS）, a linked molecular marker was developed in this study. Wheat gene chip hybridization combined with bulked segregant analysis （BSA） was used to develop an sequence-tagged sites （STS） marker for PmLK906 and Pm4. A new 2 125 bp full-length cDNA clone （GenBank accession no. EU082094） similar to csAtPR5 ofAegilops tauschii was isolated from Lankao 90（6） 21-12, and temporarily named TaAetPR5. Specific products could be amplified from cultivars or lines possessing Pm4a, Pm4b and PmLK906 with primers p9-7pl and p9-7p2 derived from TaAetPR5. TaAetPR5 was linked to PmLK906 at a genetic distance of 7.62 cM, and cosegregated with Pm4a. The p9-7p1 and p9-7p2 could be used as an STS marker for these resistance genes in wheat breeding. Because this marker was cosegregated with Pm4a, it can be used in map-based cloning of the alleles at Pm4 locus also.

Molecular mapping of a stripe rust resistance gene in Chinese wheat cultivar Mianmai 41

Stripe rust, caused by Puccinia striiformis f. sp. tritici（Pst）, is one of the most damaging diseases of wheat. Chinese wheat cultivar Mianmai 41 showed high resistance against most of the prevailing Pst races in China. Genetic analysis of the F1, F2 and F2：3 populations from a cross between Mianmai 41 and a susceptible line Mingxian 169 indicated that resistance to Pst race CYR32 was conferred by a single dominant gene, temporarily designated as Yr MY41. Molecular marker analysis placed the gene on chromosome 1B near the centromere. Six co-dominant genomic SSR markers Xwmc329, Xwmc406, Xgwm18, Xgwm131, Xgwm413, and Xbarc312, and one STS marker Xwe173 linked with the resistance gene. The two closest flanking SSR markers were Xgwm18 and Xwmc406, with genetic distances of 2.0 and 4.9 c M, respectively. A seedling test with 29 Pst isolates indicated the reaction patterns of Mianmai 41 were different from those of lines carrying Yr3, Yr9, Yr10, Yr15, Yr26, and Yr CH42 on chromosome 1B. Allelic tests indicated that Yr MY41 is likely a new allele at Yr26 locus.

Phylogeny of Saccharina and Laminaria(Laminariaceae, Laminariales, Phaeophyta) in sequence-tagged-site markers

Laminaria and Saccharina have recently been recognized as two independent clades from the former genus Laminaria. Traditional morphological taxonomy is being challenged by molecular evidence from both nucleus and plastid. Intensive work is in great demand from the perspective of genome colinearity. In this study, 118 sequence-tagged site(STS) markers were screened for phylogenetic analyses, 29 based on genome sequences, while 89 were based on expressed sequence tag(EST) sequences. EST-based STS marker development(29.37%) had an effi ciency twice as high as genome-sequence-based development(9.48%) as a result of high conservation of gene transcripts among the relative species. S. ochotensis, S. religiosa, S. japonica, and L. hyperborea showed great homogeneity in all 118 STS markers. Our result supports the view that the diversifi cation between the genera Saccharina and Laminaria was a more recent event and that Saccharina and Laminaria shared high phylogenetic affi nity. However, when it came to the single nucleotide polymorphism(SNP) level among the 41 SNPs, L. hyperborea owned 29 unique SNPs against 12 within the left three Saccharina species and 12 of the 13 indels were supposedly unique for L. hyperborea, indicated by its high variability. Originating from homologous ancestors, species between the recently diverged genera Laminaria and Saccharina may have taken in enough mutations at the SNP level only, in spite of different evolutionary strategies for better adaptation to the environment. Our study lays a solid foundation from a new perspective, although more accurate phylogenetic analysis is still needed to clarify the evolutionary traces between the genera Saccharina and Laminaria.