Variations in radioactive cesium accumulation in wheat germplasm from fields affected by the 2011 Fukushima nuclear power plant accident.

Decreasing the transfer of radioactive cesium (RCs) from soil to crops has been important since the deposition of RCs in agricultural soil owing to the Fukushima nuclear power plant accident of 2011. We investigated the genotypic variation in RCs accumulation in 234 and 198 hexaploid wheat (Triticum spp.) varieties in an affected field in 2012 and 2013, respectively. The effects of soil exchangeable potassium (ExK) content to RCs accumulation in wheat varieties were also evaluated. A test field showed fourfold differences in soil ExK contents based on location, and the wheat varieties grown in areas with lower soil ExK contents tended to have higher grain RCs concentrations. RCs concentrations of shoots, when corrected by the soil ExK content, were positively significantly correlated between years, and RCs concentrations of shoots were significantly correlated with the grain RCs concentration corrected by the soil ExK content. These results indicated that there were genotypic variations in RCs accumulation. The grain to shoot ratio of RCs also showed significant genotypic variation. Wheat varieties with low RCs accumulations were identified. They could contribute to the research and breeding of low RCs accumulating wheat and to agricultural production in the area affected by RCs deposition.

Development of self-fertile deletion homozygous and ditelosomic lines for the long arm of chromosome 2A in common wheat.

Most deletions for the short arm of chromosome 2A (2AS), and the telocentric chromosome for the long arm of chromosome 2A (2AL), are available only in the heterozygous condition in 'Chinese Spring' hexaploid wheat. This is due to the female sterility, and therefore self-sterility, of their homozygotes, caused by the partial or entire loss of the 2AS chromosome arm on which genes for normal synapsis and female fertility are located. On the other hand, a D-genome disomic substitution line 2D(2A) of 'Langdon' tetraploid wheat, in which chromosome 2D is disomically substituted for chromosome 2A, is available (i.e., self-fertile) despite chromosome 2A being missing in this line. This fact indicates that another gene for female fertility must be present in Langdon 2D(2A). We attempted to develop self-fertile 2AS homozygous deletion and ditelosomic 2AL lines by transferring this female fertility gene, through a series of crosses and cytological screening, from Langdon 2D(2A) to the two aneuploid lines. We finally obtained self-fertile 2AS homozygous deletion and ditelosomic 2AL lines. These lines displayed normal meiotic chromosome pairing and lacked all 12 of the 2AS markers used for PCR analysis.

Chromosome Arm Locations of Barley Sucrose Transporter Gene in Transgenic Winter Wheat Lines.

Three transgenic HOSUT lines of winter wheat, HOSUT12, HOSUT20, and HOSUT24, each harbor a single copy of the cDNA for the barley sucrose transporter gene HvSUT1 (SUT), which was fused to the barley endosperm-specific Hordein B1 promoter (HO; the HOSUT transgene). Previously, flow cytometry combined with PCR analysis demonstrated that the HOSUT transgene had been integrated into different wheat chromosomes: 7A, 5D, and 4A in HOSUT12, HOSUT20, and HOSUT24, respectively. In order to confirm the chromosomal location of the HOSUT transgene by a cytological approach using wheat aneuploid stocks, we crossed corresponding nullisomic-tetrasomic lines with the three HOSUT lines, namely nullisomic 7A-tetrasomic 7B with HOSUT12, nullisomic 5D-tetrasomic 5B with HOSUT20, and nullisomic 4A-tetrasomic 4B with HOSUT24. We examined the resulting chromosomal constitutions and the presence of the HOSUT transgene in the F2 progeny by means of chromosome banding and PCR. The chromosome banding patterns of the critical chromosomes in the original HOSUT lines showed no difference from those of the corresponding wild type chromosomes. The presence or absence of the critical chromosomes completely corresponded to the presence or absence of the HOSUT transgene in the F2 plants. Investigating telocentric chromosomes occurred in the F2 progeny, which were derived from the respective critical HOSUT chromosomes, we found that the HOSUT transgene was individually integrated on the long arms of chromosomes 4A, 7A, and 5D in the three HOSUT lines. Thus, in this study we verified the chromosomal locations of the transgene, which had previously been determined by flow cytometry, and moreover revealed the chromosome-arm locations of the HOSUT transgene in the HOSUT lines.

Genetic dissection of grain morphology in hexaploid wheat by analysis of the NBRP-Wheat core collection.

We investigated the genetic diversity of the core collection of hexaploid wheat accessions in the Japanese wheat gene bank, NBRP-Wheat, with a focus on grain morphology. We scanned images of grains in the core collection, which consists of 189 accessions of Triticum aestivum, T. spelta, T. compactum, T. sphaerococcum, T. macha and T. vavilovii. From the scanned images, we recorded six metric characters (area size, perimeter length, grain length, grain width, length to width ratio and circularity) using the software package SmartGrain ver. 1.2. Statistical analyses of the collected data along with hundred-grain weight revealed that T. aestivum has the largest diversity in grain morphology. Principal component analysis of these seven characters demonstrated that two principal components (PCcore1 and PCcore2) explain more than 96% of the variation in the core collection accessions. The correlation coefficients between the principal components and characters indicate that PCcore1 is related to grain size and PCcore2 to grain shape. From a genome-wide association study, we found a total of 15 significant marker-trait associations (MTAs) for grain morphological characters. More interestingly, we found mutually exclusive MTAs for PCcore1 and PCcore2 on 18 and 13 chromosomes, respectively. The results suggest that grain morphology in hexaploid wheat is determined by two factors, grain size and grain shape, which are under the control of multiple genetic loci.

Population structure and association analyses of the core collection of hexaploid accessions conserved ex situ in the Japanese gene bank NBRP-Wheat.

In this study, we investigated the genetic diversity and population structure of the core collection of hexaploid wheat accessions in the Japanese wheat gene bank NBRP-Wheat. The core collection, consisting of 188 accessions of Triticum aestivum, T. spelta, T. compactum, T. sphaerococcum, T. macha and T. vavilovii, was intensively genotyped by DArTseq markers and consisted of 20,186 SNPs and 60,077 present and absent variations (PAVs). Polymorphic markers were distributed in all chromosomes, with a tendency for smaller numbers on the D-genome chromosomes. We examined the population structure by Bayesian clustering and principal component analysis with a general linear model. Overall, the core collection was divided into seven clusters. Non-admixture accessions in each cluster indicated that the clusters reflect the geographic distribution of the accessions. Both structure analyses strongly suggested that the cluster consisting of T. spelta and T. macha is out-grouped from other hexaploid wheat accessions. We performed genome-wide association analysis pilot studies for nine quantitative and seven qualitative traits and found marker-trait associations for all traits but one, indicating that the current core collection will be useful for detecting uncharacterized QTLs associated with phenotypes of interest.

Genetic diversity of submergence stress response in cytoplasms of the Triticum-Aegilops complex.

Genetic diversity in cytoplasmic and nuclear genomes and their interaction affecting adaptive traits is an attractive research subject in plants. We addressed submergence stress response of wheat that has become increasingly important but remained largely uninvestigated. Our primary aim was to disclose cytoplasmic diversity using nucleus-cytoplasm (NC) hybrids possessing a series of heterologous cytoplasms in a common nuclear background. Effects of submergence on seedling emergence and growth from imbibed seeds were studied and compared with euplasmic lines. Marked phenotypic variabilities were observed among both lines, demonstrating divergent cytoplasmic and nuclear effects on submergence response. NC hybrids with cytoplasm of Aegilops mutica showed a less inhibition, indicative of their positive contribution to submergence tolerance, whereas cytoplasms of Aegilops umbellulata and related species caused a greater inhibition. Superoxide dismutase (SOD) activity showed a marked increase accompanied by retardation of seedling growth in a susceptible NC hybrid. The observation suggested that the elevated SOD activity was resulted from a high level of reactive oxygen species accumulated and remained in susceptible seedlings. Taken together, our results point to the usefulness of NC hybrids in further studies needed to clarify molecular mechanisms underlying the nucleus-cytoplasm interaction regulating submergence stress response in wheat.

Evolution and dispersal of emmer wheat (Triticum sp.) from novel haplotypes of Ppd-1 (photoperiod response) genes and their surrounding DNA sequences.

The sequence data from 5' UTR, intronic, coding and 3' UTR regions of Ppd-A1 and Ppd-B1 were investigated for a total of 158 accessions of emmer wheat landraces comprising 19 of wild emmer wheat (Triticum dicoccoides), 45 of hulled emmer wheat (T. dicoccum) and 94 of free-threshing (FT) emmer wheat (T. durum etc.). We detected some novel types of deletions in the coding regions from 22 hulled emmer accessions and 20 FT emmer accessions. Emmer wheat accessions with these deletions could produce predicted proteins likely to lack function. We also observed some novel mutations in Ppd-B1. Sixty-seven and forty-one haplotypes were found in Ppd-A1 and Ppd-B1, respectively. Some mutations found in this study have not been known, so they have potential for useful genetic resources for wheat breeding. On the basis of sequence data from the 5' UTR region, both Ppd-A1 and Ppd-B1 haplotypes were divided into two groups (Type AI/AII and Type BI/BII). Types AI and AII of Ppd-A1 suggested gene flow between wild and hulled emmer. On the other hand, Types BI and BII of Ppd-B1 suggested gene flow between wild and FT emmer. More than half of hulled emmer accessions were Type AII/BI but few FT emmer accessions were of this type. Therefore, over half of the hulled emmer did not contribute to evolution of FT emmer.