Distinct controls of leaf widening and elongation by light and evaporative demand in maize

Leaf expansion depends on both carbon and water availabilities. In cereals, most of experimental effort has focused on leaf elongation, with essentially hydraulic effects. We have tested if evaporative demand and light could have distinct effects on leaf elongation and widening, and if short‐term effects could translate into final leaf dimensions. For that, we have monitored leaf widening and elongation in a field experiment with temporary shading, and in a platform experiment with 15 min temporal resolution and contrasting evaporative demands. Leaf widening showed a strong (positive) sensitivity to whole‐plant intercepted light and no response to evaporative demand. Leaf elongation was (negatively) sensitive to evaporative demand, without effect of intercepted light per se. We have successfully tested resulting equations to predict leaf length and width in an external dataset of 15 field and six platform experiments. These effects also applied to a panel of 251 maize hybrids. Leaf length and width presented quantitative trait loci (QTLs) whose allelic effects largely differed between both dimensions but were consistent in the field and the platform, with high QTL × Environment interaction. It is therefore worthwhile to identify the genetic and environmental controls of leaf width and leaf length for prediction of plant leaf area.     

Results of a whole genome scan targeting QTL for growth and carcass traits in a Piétrain × Large White intercross

We herein report the results of a whole genome scan performed in a Piétrain × Large White intercross counting 525 offspring to map QTL influencing economically important growth and carcass traits. We report experiment-wide significant lod scores (> 4.6 for meatiness and fat deposition on chromosome SSC2, and for average daily gain and carcass length on chromosome SSC7. Additional suggestive lod scores (> 3.3) for fat deposition are reported on chromosomes SSC1, SSC7 and SSC13. A significant dominance deviation was found for the QTL on SSC1, while the hypothesis of an additive QTL could not be rejected for the QTL on SSC7 and SSC13. No evidence for imprinted QTL could be found for QTL other than the one previously reported on SSC2.     

Evolutionary and ecological genomics of non-model plants

Dissecting evolutionary dynamics of ecologically important traits is a long-term challenge for biologists.Attempts to understand natural variation and molecular mechanisms have motivated a move from laboratory model systems to non-model systems in diverse natural environments.Next generation sequencing methods,along with an expansion of genomic resources and tools,have fostered new links between diverse disciplines,including molecular biology,evolution,ecology,and genomics.Great progress has been made in a few non-model wild plants,such as Arabidopsis relatives,monkey flowers,and wild sunflowers.Until recently,the lack of comprehensive genomic information has limited evolutionary and ecological studies to larger QTL (quantitative trait locus) regions rather than single gene resolution,and has hindered recognition of general patterns of natural variation and local adaptation.Further efforts in accumulating genomic data and developing bioinformatic and biostatistical tools are now poised to move this field forward.Integrative national and international collaborations and research communities are needed to facilitate development in the field of evolutionary and ecological genomics.     

Single-strand conformational polymorphism markers associated with a major QTL for fusarium head blight resistance in wheat

A major quantitative trait locus (QTL) associated with resistance to Fusarium head blight (FHB) was identified on chromosome 3BS between simple sequence repeat (SSR) markers Xgwm389 and Xgwm493 in wheat “Ning 7840”, a derivative from “Sumai 3”. However, the marker density of SSR in the QTL region was much lower than that required for marker-assisted selection (MAS) and map-based cloning. The objective of this study was to exploit new markers to increase marker density in this QTL region by using single-strand conformational polymorphism (SSCP) markers developed from wheat-expressed sequence tags (ESTs) on 3BS bin 8-0.78-1.0. Sixty-nine out of 85 SSCP primer pairs amplified PCR (polymerase chain reaction) products from the genomic DNA of “Chinese Spring”. Thirty-four primer pairs amplified PCR products that could form clear ssDNA (single strand DNA) bands through denaturation treatment. Ten SSCP markers had polymorphisms between Ning 7840 and “Clark”. Five of the ten polymorphic SSCP markers were located on chromosome 3B by nullitetrasomic analysis. Three SSCP markers (Xsscp6, Xsscp20, and Xsscp21) were mapped into the region between Xgwm493 and Xgwm533 and possessed a higher coefficient of determination (R²) than Xgwm493 and Xgwm533. The SSCP markers, Xsscp6, Xsscp20, and Xsscp21, can be used for map-based cloning of the QTL and for marker-assisted selection in FHB resistance breeding.     

水稻耐盐相关动态QTL的加性和上位性与环境互作分析

钠离子(Na⁺)、钾离子(K⁺)含量和Na⁺/K⁺值是影响水稻耐盐性的关键指标。水稻的耐盐性由数量性状位点(QTL)控制,目前在水稻苗期已经鉴定了大量Na⁺、K⁺含量和Na⁺/K⁺的QTL,但在田间生长期鉴定的QTL数量较少。该研究以粳稻‘东农425’和‘长白10’杂交衍生的重组自交系(RIL)群体为材料,对田间试验条件下的盐胁迫和对照进行联合分析,在水稻不同发育时期鉴定Na⁺、K⁺含量和Na⁺/K⁺的发育动态QTL,并采用混合线性模型(MCIM)分析各QTL的加性(A)和上位性(AA)及其与环境的互作效应(QE)。结果表明：(1)盐胁迫条件下,亲本和RIL群体的茎Na⁺含量(SNC)、茎Na⁺/K⁺(SN/K)、叶Na⁺含量(LNC)和叶Na⁺/K⁺(LN/K)在各时期均高于对照,茎K⁺含量(SKC)和叶K⁺含量(LKC)均低于对照,对照条件下双亲性状在大多数时期均无显著差异;盐胁迫下两个亲本的多个性状在不同发育时期存在显著差异,其中,SNC和LKC在4个时期差异显著,SN/K和LN/K在3个时期差异显著,SKC和LNC在2个时期差异显著。(2)采用非条件和条件QTL作图方法,共检测到13个加性QTL和11对上位性QTL,其中包括14个非条件QTL和10个条件QTL;而13个加性QTL中有8个,11对上位性QTL中有7个具有环境互作效应。(3)qSKC5 1在水稻4个发育阶段均被检测到,其在调控水稻耐盐性中发挥着重要作用。SNC、SN/K和LN/K的所有QTL均检测到加性×环境互作效应,2对控制SNC的上位性QTL均检测到上位性×环境互作效应,说明这些性状的QTL对盐环境较为敏感。研究发现,田间生长条件下水稻Na⁺、K⁺含量和Na⁺/K⁺的QTL表达与发育时期密切相关;水稻田间生长条件下耐盐性的遗传非常复杂,在利用分子标记辅助选择(MAS)培育耐盐水稻新材料应该考虑上位性和环境互作效应。     

Drought tolerance in rice: morphological and molecular genetic consideration

Rice is one of the most important food crop drastically affected by drought in lowland rice ecosystem. Dissecting out the traits of importance and genomic regions influencing the response of drought tolerance and yield traits on grain yield will aid the breeders to know the genetic mechanism of drought tolerance of rice leads to the development of drought tolerant varieties. Grain yield and its components on drought situation of recombinant inbred population (IR 58821/IR 52561) were investigated under lowland managed stress situation in 2003 and 2004 by given importance to the relative water content. Water deficit resulted in significant effect on phenology and grain yield. Best lines were selected for further varietal development programme. Variability studies showed the traits viz., days to 70% relative water content, leaf rolling, leaf drying, harvest index, biomass yield and grain yield offer high scope for improvement for drought tolerance by way of simple selection technique. Correlation and path analysis indicated that, to harness high yielding combined with drought tolerance breeders should give selection pressure on relative water content, panicle length, grains per panicle, harvest index, biomass yield, root/shoot ratio and root length in positive direction, and low scores of leaf rolling, leaf drying and drought recovery rate. Analysis of quantitative trait loci for drought tolerance, yield and its components allowed the identification of 38 regions associated with both drought tolerant and yield traits. Out of these, 18 were closely linked with DNA markers could be used for marker assisted selection in breeding for drought tolerance in rice. Pleiotropism and G × E effects interaction were noticed in some of the traits. Parent IR 58821 contributed favorable alleles for the entire drought related and most of the yield component traits. Identification of traits of importance and their nature of relationship by morphological and molecular level under lowland condition will be useful to improve drought tolerance of rice.     

Re-evaluation of morphological and chloroplast DNA variation in Juniperus osteosperma Hook and Juniperus occidentalis Torr. Little (Cupressaceae) and their putative hybrids

Relationships between variation in cpDNA and morphology were examined to test the hypothesis of hybridization between Juniperus osteosperma and Juniperus occidentalis. Principal components analysis of 11 taxonomically-important characters distinguished individuals collected from eastern Nevada and Utah from those of southern Oregon. In contrast, many individuals collected from sympatric populations in western Nevada were morphologically intermediate to these two groups. Comparative sequencing of the trnS-trnG intergenic spacer and restriction site analysis of a trnL-trnF PCR product revealed nine haplotypes, and examination of haplotype-morphology associations allowed identification of species-specific genetic markers as well as those that transcend species limits. The confinement of morphological intermediacy and transcendent haplotypes to zones of sympatry, the discovery of haplotypes characteristic of one species in the morphological background of the other, and determination that the character intermediacy encountered is of the type expected under interspecific gene flow are marshaled in support of introgressive hybridization between J. osteosperma and J. occidentalis.     

Evolutionary history of the genus Capra (Mammalia, Artiodactyla): discordance between mitochondrial DNA and Y-chromosome phylogenies

The systematics of the genus Capra remain controversial in spite of studies conducted using morphology, mtDNA, and allozymes. Here, we assess the evolutionary history of Capra (i) using phylogenetic analysis of two nuclear genes located on the Y-chromosome and (ii) previously published and new cytochrome b sequences. For the Y-chromosome phylogeny, we sequenced segments from the amelogenin (AMELY) and zinc finger (ZFY) genes from all of the eight wild taxa and from domestic goats (Capra hircus). Phylogenetic analysis of the Y-chromosome data revealed two well-defined clades. The domestic goat (C. hircus), the bezoar (Capra aegagrus), and the markhor (C. falconeri) belong to one clade (ML bootstrap value [BP]: 98%), suggesting that domestic goats originated from one or both of these wild species. The second clade (ML BP: 92%) is comprised of all the other wild species. Horn morphology is generally concordant with the Y-chromosome phylogeny. The mtDNA data also revealed two well-defined clades. However, the species in each clade are different from those inferred from the Y-chromosome data. To explain the discordance between Y-chromosome and mtDNA phylogenies, several hypotheses are considered. We suggest that a plausible scenario involves mtDNA introgression between ancestral taxa before the relatively recent colonization of Western Europe, the Caucasus Mountains, and East Africa by Capra populations.     

玉米花期耐旱导入系群体的构建与评价

以黄早四X齐319回交群体（BC2F1）为试验材料,在花期进行高强度干旱胁迫和耐旱导入系筛选,获得花期耐旱性显著高于亲本材料的玉米耐旱导入系。利用分子标记对其导入片段进行分析结果表明,在全基因组范围内,耐旱群体在36．59％的位点上含有供体亲本的特异标记,尤其在第4、5染色体上分别达到63．94％、56％,显著高于群体平均值;同时发现,导入频率的提高主要集中于染色体的部分区段,其中部分基因组区域与已定位的耐旱性相关QTL相邻或重叠。     

Introgression into the allotetraploid coffee ( Coffea arabica L.): segregation and recombination of the C. canephora genome in the tetraploid interspecific hybrid ( C. arabicax C. canephora)

Transfer of desired characters from the diploid relative species such as Coffea canephora into the cultivated allotetraploid coffee species (Coffea arabica L.) is essential to the continued improvement of varieties. Behaviour of the C. canephora genome and its interaction with the C. arabica genome were investigated in tetraploid interspecific hybrids (C. arabica×C. canephora 4x) resulting from a cross between an accession of C. arabica and a tetraploid plant of C. canephora obtained following colchicine treatment. Segregation and co-segregation of restriction fragment length polymorphism (RFLP) and microsatellite loci-markers were studied in two BC₁ populations. These two populations of 28 and 45 individuals, respectively, resulted from the backcross of two tetraploid F₁ plants to C. arabica. The presence in BC₁ plants of specific C. canephora markers was scored for 24 loci (11 RFLP and 13 microsatellites) distributed on at least 7 of the 11 linkage groups identified in C. canephora. At almost all loci analysed, the segregation of C. canephora alleles transmitted by the (C. arabica×C. canephora 4x) hybrids conformed to the expected ratio assuming random chromosome segregation and the absence of selection. The recombination fractions of C. canephora chromosome segments were estimated for seven marker intervals, and compared with the recombination fractions previously observed in C. canephora for the equivalent marker intervals. The recombination frequencies estimated in both plant materials were rather similar, suggesting that recombination in the (C. arabica×C. canephora 4x) hybrid is not significantly restricted by the genetic differentiation between chromosomes belonging to the different genomes. The hybrid (C. arabica×C. canephora 4x) therefore appeared particularly favourable to intergenomic recombination events and gene introgressions. Received: 26 March 2001 / Accepted: 29 June 2001