Many hermaphrodite plant species have evolved mechanisms to prevent self-fertilization. One such mechanism is self-incompatibility (SI), which is defined as the inability of a fertile hermaphrodite plant to produce zygotes after self-pollination. SI prevents self-fertilization by rejecting pollen from plants with the same genotype. The SI system in Brassica is controlled sporophytically by multiple alleles at a single locus, designated as S, and involves cell-cell communication between male and female. When the S phenotype of the pollen is the same as that of the stigma, pollen germination and/or pollen tube penetration are disturbed on the papilla cells. On the female side, two genes (SLG and SRK) located at the S locus, are involved in the SI reaction. SLG is a secreted glycoprotein expressed abundantly in the papilla cell, and SRK is a membrane-spanning receptor-like serine/threonine kinase whose extracellular domain is highly similar to SLG. Gain-of-function experiments have demonstrated that SRK solely determines S haplotype-specificity of the stigma, while SLG enhances the recognition reaction of SI. The sequence analysis of the S locus genomic region of Brassica campestris (syn. rapa) has led to the identification of an anther-specific gene, designated as SP11, which encodes a small cysteine-rich basic protein. Pollination bioassay and gain-of-function experiments have indicated that SP11 is the male S determinant. When the sequence of SP11 was aligned, six cysteine residues were found to be completely conserved among alleles. These conserved cysteine residues could be important for the tertiary structure of SP11. Recent biochemical analysis has suggested that SP11 operates as a sole ligand to activate its cognate SRK specifically. Because the activity of the S allele is controlled sporophytically, dominance relationships influence the ultimate phenotype of both the stigma and pollen. Molecular analysis has demonstrated that the dominance relationships between S alleles in the stigma were determined by SRK itself, but not by the relative expression level. In contrast, in the pollen, the expression of SP11 from the recessive S allele was specifically suppressed in the S heterozygote, suggesting that the dominance relationships in pollen were determined by the expression level of SP11.
Backcross inbred lines (BILs) derived from a cross of Nipponbare (japonica) / Kasalath (indica) // Nipponbare were used to identify quantitative trait loci (QTLs) controlling physico-chemical properties of rice grains such as amylose content (AC), alkali spreading score (ASS) and gel consistency (GC) by composite interval mapping over a period of two years. A total of 4 QTLs for AC were detected; qAC-5 and qAC-6 showed significant effects (hereafter referred to as “significant”) in both years, and qAC-6 explained more than 80 % of the phenotypic variance and was located in the wx region on the short arm of chromosome 6. The other 2 QTLs for AC with small additive effects were detected and were significant only in one year. Three QTLs for ASS were identified; qASS-6a and qASS-6b were significant in both years, and qASS-6a corresponded to a major gene located in the alk region on chromosome 6, while qASS-3 on chromosome 3 was significant only in one year. Five QTLs for GC were detected and all were significant only in one year. The lock of detection of major gene(s) for GC may be due to the fact that none of the parents were differentiated in terms of GC. These results showed that AC and ASS were mainly controlled by known gene loci, i.e., wx and alk, respectively, with modification by minor genes.
The relationship between the protein content of soybean seeds and the consistency of tofu was examined for six Japanese soybean varieties, Enrei, Fukuyutaka, Sachiyutaka, Ayakogane, Hatayutaka and Tachinagaha. The seed protein content was estimated by determining the nitrogen content using the Dumas method. Tofu was prepared from a raw homogenate of water-soaked soybeans by heating and by the addition of MgCl2 as a coagulant. The tofu consistency was evaluated by measuring the breaking stress of tofu curd using a Creep meter. The breaking stress of tofu increased when the concentrations of MgCl2 in soymilk increased above 0.20 %. The breaking stress reached a maximum value at concentrations of around 0.40 %, with differences among soybean varieties and cultivation conditions of the soybeans. There was a significant positive correlation (r = 0.87) between the maximum breaking stress of tofu and the seed protein content for the six varieties. In contrast, the breaking stress of tofu prepared with 0.25 % MgCl2 did not show a significant correlation (r = 0.27) with the seed protein content for the six varieties but was significantly correlated (r = 0.52), when the data of Sachiyutaka were excluded. Fukuyutaka and Ayakogane required a lower MgCl2 concentration for the maximum breaking stress of tofu than Sachiyutaka, Enrei, Tachinagaha and Hatayutaka, which required a MgCl2 concentration above 0.40 % for the maximum breaking stress of tofu. Especially, Sachiyutaka required the highest MgCl2 concentration, 0.45 % on the average, for the maximum breaking stress of tofu among the six varieties. Sachiyutaka-tofu showed the lowest breaking stress on the average at a concentration of 0.25 % MgCl2, which is the concentration generally used by manufacturers, in spite of its high content in seed protein. In contrast, Fukuyutaka required the lowest MgCl2 concentration, 0.34 % on the average, for the maximum breaking stress and the highest breaking stress of tofu prepared with 0.25 % MgCl2. That is one of reasons why manufacturers prefer to use Fukuyutaka for producing tofu. Concentration of a coagulant for the maximum breaking stress as well as seed protein content could become criteria for quality evaluation of soybeans for tofu processing.
To establish a Marker Assisted Selection (MAS) system for lines with a low occurrence of hull-cracked grain in malting barley, we screened about 1,000 DNA markers to detect polymorphisms between Kinuyutaka (low occurrence of hull-cracked grain) and Yoshikei 15 (high occurrence of hull-cracked grain). Then, we constructed a genetic map for Kinuyutaka × Yoshikei 15 using 150 doubled haploid lines (DHLs) with 55 polymorphic DNA markers. This map covered 546.8 cM and eight linkage groups on seven barley chromosomes. The QTL analyses revealed three QTLs for the hull-cracked grain on barley chromosomes 2H, 3H and 6H. These DNA markers on three QTLs are important for selecting tolerant lines for hull-cracked grain.
In intergeneric crossings between Diplotaxis tenuifolia (2n = 22, DtDt) and five cultivars of Raphanus sativus (2n = 18, RR), an intergeneric F1 hybrid was produced from the crossing of D. tenuifolia × R. sativus cv. ‘4-season leaf’ through ovary culture followed by embryo culture. The induced amphidiploid (2n = 40, DtDtRR) showed well-regulated meiotic features at PMCs and a high pollen fertility (75 %). Three BC1 hybrids with DtRR (2n = 29) or DtDtR (2n = 31) genome constitutions were obtained by the same embryo rescue procedure in the crossings of amphidiploid × R. sativus and D. tenuifolia × amphidiploid, respectively. In the successive backcrossings of two BC1 hybrids (DtRR, 2n = 29) to R. sativus, 102 BC2 hybrids were obtained by conventional pollination. In the reciprocal crossing of R. sativus × BC1 hybrids, 12 reciprocal BC2 hybrids were also produced without embryo rescue. The somatic chromosome number of 89 BC2 hybrids with D. tenuifolia cytoplasm and 12 reciprocal BC2 hybrids with R. sativus cytoplasm ranged from 2n = 18 to 2n = 23 that were estimated to carry 2n = 18 chromosomes of R. sativus and zero to five chromosomes of D. tenuifolia. Among them, 24.7 % of the BC2 hybrids and 41.6 % of the reciprocal BC2 hybrids were assumed to be monosomic addition lines (MALs, 2n = 19). The novel intergeneric hybrids obtained in this study could become useful materials for investigating the genetic effects on C3-C 4 intermediate traits at the genomic and chromosomal levels, as well as for estimating the performance of genetic improvement in Brassicaceae.
Norin-PL11 (PL11) is a highly cool-tolerant line which contains genes for cool tolerance introduced from ‘Padi Labou Alumbis’, a landrace of Borneo. We investigated whether the dwarfing gene d18-k (kotaketamanishiki dwarf) exerts its pleiotropic effect of enhancing the cool tolerance at the booting stage under the genetic background of PL11, using the d18-k isogenic line of the recurrent parent PL11 (D11). During the booting stage, two cool-air treatments at 12°C for five days with and without deep water of 15 cm depth (DW and CA treatments, respectively) were conducted in growth chambers illuminated at about 600 μmol PAR m−2 s−1. Besides spikelet fertility, the ratio (%) of the fertilized-spikelet number of each treated panicle to the varietal mean of fertilized-spikelet number per panicle in the control, viz. FS-T/C was adopted in order to estimate the extent of cool damage including the factor of spikelet degeneration. The CA treatment induced notable spikelet degeneration in PL11, but not in D11. The parameter L5, which is the average of the lowest five FS-T/C values (or spikelet fertilities) on five consecutive days in each line, was used for evaluating the cool tolerances of the lines. In the CA treatment, D11 had a higher L5 in FS-T/C than PL11, indicating that D11 is more cool-tolerant than PL11. D11 showed a significantly higher L5 of FS-T/C in the DW treatment than in the CA treatment, but PL11 showed no significant difference of L5 between the CA and DW treatments. Similar results were obtained for spikelet fertility. In D11, almost the whole panicle at the most susceptible stage was under the surface of the deep water. On the other hand, the whole panicle was above the water surface at that stage in PL11. Consequently, D11 almost eluded the damage from the severe cool-air treatment when combined with the deep water. D11 exceeded PL11 not only in ripened pollen grain number per anther in the control but also in an indicator of pollen fertility after the CA treatment, owing to the effects of d18-k. It is concluded that d18-k may be useful for developing super-highly cool-tolerant cultivars for cool-weather areas.
GL2-type genes have been recognized as plant-specific homeobox genes involved in epidermis development. Here we report the isolation and characterization of rice GL2-type homeobox genes. The BLAST searches using the rice genomic database revealed that there are at least nine GL2-type homeobox genes (Roc1-Roc9) in the rice genome. Among them, we have isolated full cDNA clones of five Roc genes, including previously reported Roc1. GL2-type homeodomain proteins have a dimerization motif, consisting of two leucine zipper-like motifs (LZ1 and LZ2) interrupted by a loop, adjacent to the C-terminal part of the homeodomain. The Roc proteins can form both homo- and hetero-dimers through leucine zipper motifs in various combinations. In situ hybridization, RNA gel blot analysis and RT-PCR experiment revealed that the five Roc genes commonly showed an epidermis-specific expression, but partially differed in the temporal expression pattern. These results suggest that the Roc genes can regulate a variety of processes in epidermis differentiation in a combinatorial way.
One hundred and ninety-one recombinant inbred lines (RILs) (F7) derived from a cross between Milyang 23 (M23) and Akihikari (AK) were grown in 1997 in Joetsu, Japan (temperate zone), and during the 2000-01 dry and wet seasons (four consecutive seasons) in Los Baños, Philippines (tropical zone) to detect quantitative trait loci (QTLs) for flag leaf length, width and angle (FLL, FLW and FLA) of rice (Oryza sativa L.). The detected QTLs suggested that flag leaf development was influenced by nine genomic regions categorized into three groups. In Group I, three regions (chromosomes 1, 4 and 6) increased both FLL and FLW. The QTL profiles showed that the effects of these three regions were powerful and stable across locations. Especially, the effect of the region on chromosome 4 (the nearest RFLP marker, XNpb235) accounted for 9–17 % and 20–26 % of the FLL and FLW variances, respectively. In Group II, four regions (chromosomes 2, 3, 10 and 11) affected FLL, whereas in Group III, two regions (chromosomes 8 and 12) affected FLW. The detection pattern of QTLs showed that three regions in Groups II and III (chromosomes 3, 10 and 12) were expressed by the growth conditions of Los Baños. No region with a clear effect on FLA was identified, although this trait was segregated largely in the RILs. By characterizing the nine regions in detail, this paper elaborates on the genetic factors and mechanisms controlling flag leaf development.
An incompletely dominant gene Ur1 (Undulate rachis -1) increases spikelet number per panicle owing to increase of secondary branches. This genic effect on spikelet number can increase grain yield in either the Ur1/Ur1 or Ur1/+ genotype by enlarging sink size. We examined whether the yield-increasing effect of Ur1 in the heterozygous genotype can be superimposed upon the high yield ability of a japonica F1 hybrid. Two F1s with and without Ur1 (HU and H+) were produced by the hybridization between ‘Nishihikari’ (common maternal parent, short-culm variety) and the isogenic line of Taichung 65 possessing both Ur1 and sd1 or that carrying sd1 only. In 1999, HU, H+ and ‘Hinohikari’, a leading variety in southern Japan, were grown under three fertilizer levels. ‘Nishihikari’ was included in the experiment only at the middle fertilizer level. In 2000, HU and ‘Hinohikari’ were grown at the twofold (heavy) fertilizer level. H+ had a 21 % higher yield than ‘Nishihikari’, revealing its heterobeltiosis. The yield of H+ was 12 to 15 % higher under the three fertilizer levels than that of the check variety ‘Hinohikari’. H+ had a higher ripened-grain percentage than either ‘Hinohikari’ or ‘Nishihikari’. HU had a 7, 10 and 11 % higher yield, respectively, at the low, middle and high fertilizer levels than H+. Among the four yield components, spikelet number per panicle alone contributed to the higher yield of HU, even though its ripened-grain percentage was lower than that of H+. In yield, both F1s showed positive responses from the middle to high fertilizer levels but little response from the low to middle fertilizer levels. HU showed 22, 25 and 24 % (116, 126 and 137 g/m2) higher yield, respectively, at the low, middle and high fertilizer levels in 1999 than ‘Hinohikari’. HU gained the highest yield, 723 g/m2 at the twofold fertilizer level in 2000 which was 14 % (88 g/m 2) higher than that of ‘Hinohikari’. Thus, the yield-increasing effect of Ur1 was superimposed upon the high yield ability of H+. Consequently, Ur1 could be utilized for developing high yielding F1 varieties in the Ur1/+ genotype.