A wheat cold-responsive gene, Wcor14, encodes a chloroplast-targeted polypeptide of 14 kDa with a putative N- terminal transit peptide. The Wcor14 gene expression was specifically regulated by low temperature and not induced by ABA, drought and salinity. Accumulation of the Wcor14 transcript and the WCOR14 protein occurred in a coordinate fashion under cold acclimation; the protein accumulation precisely followed the transcript accumulation with a clear time lag. The time course of the transcript and protein accumulation also showed a good correlation with the developmental time course and the level of freezing tolerance in two wheat cultivars. Importantly, the winter-hardy cultivar M808 accumulated larger amounts of the transcript and protein more rapidly and for a longer period than the spring-type cultivar CS. A de-acclimation study clearly showed that the WCOR14 protein was more stable also under the normal temperature condition in M808 than in CS. Accumulation of the WCOR14 protein was maintained throughout at least two months under the low temperature condition. Studies using the near-isogenic lines of Vrn loci suggested that the transcript and protein accumulation was regulated either by the Vrn genes or by the Fr genes, which are linked with the Vrn genes. In vitro phosphorylation study showed that the recombinant WCOR14 protein was a substrate for a 50 kDa wheat kinase. The activity of this kinase was modulated by low temperature in a similar manner to the Wcor14 gene expression.
O-5 S. Takumi1, R. Morimoto1, T.
Kosugi1, H. Koga2 and C. Nakamura1
(1Fac Agr, Kobe Univ, 2Res Inst Agr Res,
Ishikawa Agr Col)
Ectopic expression of Kn1 -type homeobox genes in a wheat
Hooded mutant
Hooded (Hd) is well known to be one of dominant inhibitors of awn development in common wheat ( Triticum aestivum L.). The Hd near-isogenic lines of S-615, in which the Hd locus from CS is introgressed, show not only repressed awn growth but also knot-formation at the awn base. The knot-formation is associated with the altered cell morphology and abnormal cell division under the epidermal layer at the awn base and at the top of lemma. The map location of the Hd alleles showed the chromosomal synteny among the wheat Hd, barley Hooded (K) and maize Knotted1 (Kn1). The Kn1 and K phenotypes were respectively caused by structural mutations occurred in the long intron of the maize Kn1 homeobox gene and its barley orthologue. Overexpression of the wheat class 1 Kn1-type homeobox gene exhibited abnormal leaf morphology with occasional ectopic leaves on the adaxial leaf surface in the transgenic tobacco, while no mutations possibly associated with the dominant phenotype were found in the wheat 4A loci of the Kn1 orthologue Wknox1. To find a responsive gene, we compared sequences of RT-PCR products amplified from lemma of S-615 with those from the Hd near-isogenic line. We observed ectopic expression of one Kn1-type homeobox gene homologous to Knox3. These results suggest that the wheat Hd gene is an ectopically expressed dominant Knox3 allele closely linked with the Wknox1 locus on the wheat chromosome 4A.
O-6 M. Matsumoto, I. Endo and N. Kawakami (Fac Agric, Meiji
Univ)
Effect of temperature on germination and phytohormone response In
wheat seeds
Low ambient temperature is the main environmental factor for pre-harvest sprouting of wheat. The grains of cultivar Gifu-komugi have shown to have very strong dormancy. Imbibition of the dormant grains at low temperature (5oC for 4 days), however, eliminated dormancy fairly and reduced abscisic acid (ABA) sensitivity of the embryos. We also examined the effect of temperature on germination and post-germinative growth in a gibberrelic acid (GA) insensitive near isogenic line, Rht-B1c. Germination percentages of after-ripened grains were not clearly different between Rht-B1a (CS) and Rht-B1c after imbibition for 7 days at low temperature (5 to 20oC). At 30oC, however, 88% of Rht-B1a grains germinated but only 26% of Rht-B1c grains germinated. Lengths of roots and shoots of Rht-B1c seedlings were shorter than those of Rht-B1a at 25oC and 30oC, but the lengths were not different between the two genotypes at low temperature (15oC and 5oC) conditions. These results suggest that low temperature abolishes and high temperature enhances the suppressive effect of Rht-B1c on GA response, including germination and post- germinative growth. Temperature might affect dormancy and germination of wheat grains through adjustment of ABA and GA signaling.
O-7 T. Sasanuma1,2, K. Chabane3
and J. Valkoun3 (1Grad Sch Agri, Kyoto
Univ, 2Kihara Inst Biol Res, Yohokaha City Univ,
3Genet Resour Unit, ICARDA)
AFLP analysis of genetic diversity and phylogenetic relationship
of seven diploid Aegilops species
To evaluate the genetic diversity of genus Aegilops and to clarify its phylogeny, genetic variation of seven diploid Aegilops species (Ae. umbellulata, Ae. caudata, Ae. tauschii, Ae. speltoides, Ae. bicornis, Ae. searsii, Ae. mutica) were investigated with amplified fragment length polymorphism (AFLP) technique. Five accessions from each species, thus, a total of 35 accessions were used in this study. Four primer combinations were used for the analysis of intraspecific genetic diversity and 15 primer combinations were used for that of interspecific phylogenetic relationship. As for the genetic diversity within a species, Ae. speltoides and Ae. mutica had the highest level of variation, followed by Ae. umbellulata, Ae. caudata, Ae. bicornis and Ae. searsii. Ae. tauschii had the lowest level of variation. In general, geographical relationship among populations was detected for each species. In the phylogenetic analysis, three Sitopsis species formed a cluster. The C and U genome species formed another cluster. These results are more consistent with the result of the cytological genome analysis than with that of the molecular plasmon analysis, suggesting that the nuclear genome have evolved differently from the cytoplasmic genome m genus Aegilops.