小麦矮缩病毒引起的植株矮化与赤霉素代谢的相关性分析

【目的】由异沙叶蝉(Psammotettix alienus)传播的小麦矮缩病毒病是近年来中国西北部麦区严重发生的小麦病毒病害之一。受侵染的小麦植株严重矮化,有效分蘖减少,产量损失严重。论文旨在明确小麦矮缩病毒(Wheat dwarf virus,WDV)侵染小麦植株后矮化症状形成与赤霉素代谢调控的关系,为该病害的防治打下基础。【方法】以小麦品种扬麦12为试验材料,以异沙叶蝉为传毒介体饲毒后转移到1叶期的健康幼苗(3头/株)上进行传毒,同时以无毒异沙叶蝉取食健康幼苗为对照。根据试验需要,不同时间取样备用。为保证试验的准确性,经PCR检测为阳性的作为处理组试验材料;采用间接酶联免疫吸附(ELISA)法,利用植物赤霉素(GA3)试剂盒测定分析侵染第21天取样的小麦叶片赤霉素含量;将带毒条沙叶蝉接种的小麦苗分为两个平行处理组,接种后第7天分别用GA3(浓度为50 mg·L-1)和H2O进行叶面喷施处理,每隔一周处理一次。以无毒叶蝉接种后长势一致的小麦苗作为对照组,根据株高统计结果分析外施赤霉素对受侵染小麦植株的表型变化;以山羊草(Aegilops tauschii)的内根-贝壳杉烯合成酶(ent-kaurene synthase-like 3,KSL3)的基因编码区序列为参考基因设计引物(KSL3-F:5′-ATGATGGTGAATCCGCCGC-3′;KSL3-R:5′-TTAATGGTTGATCTTTGTTT-3′),对扬麦12的KSL3进行克隆和序列分析;分别取接种后7、14和21 d的小麦植株叶片,提取RNA后反转录,以克隆得到的Ta KSL3基因序列设计引物(Ta KSL3-F:5′-GAGACATGTGCCATGGCGTTC-3′;Ta KSL3-R:5′-CGTGTCACTCAGATCGGTGGAG-3′),选择小麦翻译延伸因子1A(EF-1α)作为内参基因,利用荧光定量PCR方法分析赤霉素代谢相关基因的转录水平。【结果】经ELISA检测发现,接种21 d的发病植株赤霉素含量与健康植株相比降低了28.9%;通过施用浓度为50 mg·L-1的赤霉素后,发病植株的平均株高相比对照组显著增加35.9%;采用同源克隆得到了完整的小麦赤霉素合成途径关键酶KSL3的编码区序列,长度为1 827 bp,编码608个氨基酸,BLAST比对分析发现该DNA序列与山羊草KSL3编码区序列相似度为85.2%。经荧光定量检测发现受小麦矮缩病毒侵染后小麦KSL3表达量显著下降,接种14 d降低为对照组的35.7%,21 d降低为对照组的9.6%。【结论】小麦矮缩病毒的侵染导致赤霉素合成途径关键酶的表达量降低,可能使赤霉素合成受阻,赤霉素含量降低引发受赤霉素调节的细胞生物学过程异常,从而诱导矮化症状形成。研究结果为揭示小麦矮缩病毒侵染的致病机理和病害防控打下了基础。     

苹果矮化砧木GA20氧化酶基因的克隆及其表达分析

为了研究GA20氧化酶基因在苹果矮化砧木中的分子特征和表达特征,利用RT-PCR方法从苹果矮化砧木2号和36号c DNA中克隆了GA20氧化酶基因(GA20ox1),并对该基因及其编码氨基酸序列以及在不同时期砧木及嫁接品种中的表达分别进行了分析。结果表明,GA20ox1基因c DNA编码序列长1 179 bp,推导编码393个氨基酸(包括终止密码子),预测蛋白相对分子质量44.3 k Da,理论等电点5.89,编码的蛋白质包含GA20ox1基因家族所具有的特征保守结构域,系统进化分析表明该蛋白序列与苹果SH40的同源性达到96.9%。实时荧光定量PCR分析显示:36号砧木在6月份GA20ox1基因表达强度显著低于八棱海棠对照,而7-8月份的均显著高于对照,其上嫁接的品种7月份表达强度显著低于对照。在7-8月份2号砧木及嫁接品种GA20ox1基因的表达强度均显著低于对照。     

苹果矮化砧木致矮机理研究进展

矮化密植栽培是现代苹果生产发展的方向,苹果矮化砧是实现苹果矮化密植栽培的主要途径,其致矮机理尚不清楚。揭示苹果矮化砧致矮机理,对加快苹果矮砧育种进程和改进苹果矮砧栽培技术有重要的意义。在总结前人对致矮基因、解剖结构、水分、物质运输、光合特性、酶与酚类物质、激素等7个方面研究进展的基础上,对致矮部位及致矮机理进行了探讨,提出苹果砧木致矮是矮化砧嫁接口、砧段的木质部及韧皮部综合作用的结果,嫁接的矮砧砧段是致矮的主要部位,苹果矮砧可能通过影响根系发育起到致矮作用,并指出今后应利用更为先进的显微仪器和测量软件对苹果矮砧和乔砧砧段解剖结构进行更微观精确地比较;在严格控制环境的条件下,尽量采取一致的试材,分析不同矮化性砧木在水分、矿质营养、同化物等物质代谢过程中的生理生化变化;借助分子生物学技术对植物激素物质合成、信号转导、降解及其互作在致矮中所起的作用进行更深入系统地研究,通过多方面研究对提出的问题进行研究验证,以求对苹果矮砧致矮机理解释更加透彻。     

库尔勒香梨砧木组织培养

试验选用库尔勒香梨矮化中间砧S系、F系中的品种嫩茎尖作为试验材料进行了离体增殖研究,结果表明,不同种类的基本培养基及不同浓度配比的植物生长调节剂对试管苗增殖的效果不同。M S培养基较A S、B5培养基更有利于矮化砧S系、F系茎的增殖,中等浓度的细胞分裂素(BA)与较低浓度的生长素(IBA)、赤霉素(GA3)配合使用效果更理想。综合茎质量、茎数量等指标认为:M S BA 1.0 m g/L IBA 0.05 m g/L GA31.0 m g/L是矮化砧S系、F系试管苗茎增殖的最佳培养基。     

不同矮化中间砧对金冠苹果树体及根系生长发育的影响

本试验以嫁接不同矮化中间砧的2年生盆栽金冠苹果树为试材,研究不同矮化砧木对金冠树体及根系生长发育的影响。结果表明,不同矮化中间砧影响金冠苹果树体及根系的生长发育。中间砧为GM256的金冠苹果,树体高度及新梢生长量最大,除根系直径外,其余根系形态指标也均为最大值,树体矮化效果最差;SH1树体矮化效果最好;SH6矮化中间砧木与接穗亲和性最好,辽砧2号组合的亲和性最差;d≦0.5mm根径级的毛细根为金冠苹果幼树根系中的主要组成部分。     

Studies of Multi-Allelic Polymorphism of Dominant Dwarfing Genes in Wheat

Dwarfing breeding of wheat in the world is confined to the exploitation of recessive dwarfing sources. None of the dominant dwarfing sources discovered in common wheat (Triticum aestivum L. ) has found wide exploitation in wheat breeding due to the extreme dwarfness of their plants (20 -55 cm). We found in our work that some stable mutant lines with their plant height enhanced to different extents could be obtained in large populations derived from the stock seeds of the dominant dwarfing sources Aibian1 carrying Rht10 on 4DS and being 20 - 55 cm tall and Aisu2 carrying Rht3 on 4BS and being 55 cm tall, or from their descendants of induced mutation treatments, or from the segregating descendants of their crosses with mid- or tall-statured genotypes. Subsequently, we studied these mutation-derived lines differing in plant height with near isogenic lines and observed that the character of their enhanced plant height bred true, each carrying a semidominant dwarfing gene for a definite height and that as the plant height of the mutation-derived lines increased, the yield-contributing characters of their near isogenic lines were significantly improved. When test crosses with marker genes and physiological and biochemical genetic marker tests were performed to re-localize the semi-dominant dwarfing genes carried by the mutation-derived lines, it was confirmed that they shared common loci with Rht10 and Rht3 and that they were all mutation-derived multiple alleles. It is thus speculated that dominant dwarfing genes are of "multi-allelic polymorphism". In other words, dominant dwarfing genes, which are ultra-dwarfing, are liable to develop by mutation into a group of multiple alleles with plant height enhanced to different extents and some may have a height close to the ideal plant height for wheat breeding. Therefore, these results offer a fundamentally new approach for the exploitation of dominant dwarfing sources in wheat breeding.     

Pleiotropic effect of the dwarfing gene d18-k on cool tolerance at booting stage under the genetic background of an extremely cool-tolerant line Norin-PL8 in rice

Norin‐PL8 (‘PL8’) is an extremely cool‐tolerant line of rice in Japan that contains genes for cool tolerance originating from a javanica landrace. It was investigated to see whether the dwarfing gene d18‐k (kotaketamanishiki dwarf) exerts its pleiotropic effect on enhancing the cool tolerance at the booting stage in the genetic background of PL8. The d18‐k isogenic line of the recurrent parent PL8 (D8), PL8, and two commercial cultivars ‘Hayayuki’ and ‘Kirara 397’ were used. For each line/cultivar, the 12°C‐5‐day treatment was conducted at various times during the booting stage. In addition to 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 (FS‐T/C) was adopted to estimate cool temperature damage. For FS‐T/C, the lines‐cultivars ranked in the order of D8 > PL8 > ‘Hayayuki’ > ‘Kirara 397’, reflecting their cool tolerances. D8 exceeded PL8 in both pollen grain number per anther in the control and as an indicator of pollen fertility after the treatment, as a result of the effects of d18‐k. Consequently, d18‐k can be used to develop super‐highly cool‐tolerant cultivars for cool‐weather areas.     

Allelic variation, sequence determination and microsatellite screening at the XGWM261 locus in Chinese hexaploid wheat (Triticum aestivum) varieties

Wheat microsatellite XGWM261, due to its closely linked to the dwarfing gene Rht8, has been adopted as the diagnostic molecular marker of Rht8. Screening 408 Chinese and 98 exotic varieties showed 13 allele variants in locus of XGWM261, with 6 alleles only to be found in Chinese varieties and 2 only in exotic varieties, respectively. Sequencing results of the 13 alleles revealed their absolute fragment sizes with 216, 212, 210, 206, 204, 202, 200, 196, 194, 192, 190, 174, and 164 bp, respectively. Allelic distribution analysis showed that the 204, 192, 174, and 164 bp alleles were prevailing in Chinese varieties, and the diagnostic 192 bp allele to Rht8 had a very high percentage in the Yellow and Huai River Valleys Facultative Wheat Zone than in the Northern Winter Wheat Zone in China. The GT → AC substitution at position 35 was found in 216, 200, and 174 bp alleles. Moreover, the AG insertion immediately at the end of CT-repeat region was also found in 216, 200, 174, and 164 bp alleles.     

Indentification of true genetic dwarfing sources in foxtail millet (Setaria italica Beauv.)

Summary True genetic dwarfs hither-to not reported have been located in foxtail millet. The dwarfs as a group distinguished themselves from the talls in having altered constellation of characters. The morphological differences were highly significant for plant height, internodal length, and tillering potential. The talls had elongated internodes compared to dwarfs while there was no difference for node number on the main stem suggesting that short internodal length was primarily responsible for dwarfism. The dwarfs also showed slightly higher leaf number per plant, leaf area and harvest index compared to talls. The dwarfs were insensitive to exogenous GA₃ application indicating that GA₃ synthesis is not impaired. This suggests that dwarfing gene sources presently identified are true genetic dwarfs and their behaviour is similar to dwarfs derived from Norin 10 in wheat and Dee-geo-woo-gen in rice. The superior morphological frame makes these dwarfs ideal as far as plant type is concerned and offers immense potentialities in breeding high yielding foxtail millets.     

The effect of major dwarfing genes on yield potential in spring wheats

Summary A composite convergent cross of 16 spring wheat parents produced a set of unselected progeny lines among which the major dwarfing genes, Rht1, Rht2 and Rht3, were distributed against a common random genetic background. Random subsets of these lines were grown under irrigation and optimal conditions in 4 experiments with replicated bordered plots in southern New South Wales in order to measure the dwarfing gene effect on yield potential. The dwarfing gene composition of each line was determined by test crossing and seedling responsiveness to gibberellic acid.Lodging was negligible in the two experiments in 1982. While present in the two in 1983, it was not strongly associated with yield. Grain yield levels were appropriately high (mean 5.9 t/ha). In all but 1 experiment the Rht1+Rht2 dwarf genotypes gave highest yields while the Rht3 group yielded on average 3% lower, Rht2 9% lower, Rht1 11% lower, and the non-dwarf or tall group yielded 24% lower. These yield differences were positively associated with harvest index, kernels per m² and kernels per spike, but negatively associated with mature plant height. Even within major dwarfing gene classes, grain yield was significantly and negatively associated with height.