Distribution of Ty3-gypsy- and Ty1-copia-like DNA sequences in the genus Helianthus and other Asteraceae.

Two repeated DNA sequences, pHaS13 and pHaS211, which revealed similarity to the int gene of Ty3-gypsy retrotransposons and the RNAse-H gene of Ty1-copia retroelements, respectively, were surveyed in Asteraceae species and within the genus Helianthus. Southern analysis of the genome of selected Asteraceae that belong to different tribes showed that pHaS13- and pHaS211-related subfamilies of gypsy- and copia-like retroelements are highly redundant only in Helianthus and, to a lesser extent, in Tithonia, a Helianthus strict relative. However, under low stringency posthybridization washes, bands were observed in almost all the other Asteraceae tested when pHaS13 was used as a probe, and in several species when pHaS211 was hybridized. FISH analysis of pHaS13 or pHaS211 probes was performed in species in which labelling was observed in Southern hybridizations carried out under high stringency conditions (Helianthus annuus, Tithonia rotundifolia, Ageratum spp., Leontopodium spp., Senecio vulgaris for pHaS13, and H. annuus, Tithonia rotundifolia, and S. vulgaris for pHaS211). Scattered labelling was observed over all metaphase chromosomes, indicating a large dispersal of both Ty3-gypsy- and Ty1-copia-like retroelements. However, preferential localization of Ty3-gypsy-like sequences at centromeric chromosome regions was observed in all of the species studies but one, even in species in which pHaS13-related elements are poorly represented. Ty1-copia-like sequences showed preferential localization at the chromosome ends only in H. annuus. To study the evolution of gypsy- and copia-like retrotransposons in Helianthus, cladograms were built based on the Southern blot hybridization patterns of pHaS13 or pHaS211 sequences to DNA digests of several species of this genus. Both cladograms agree in splitting the genomes studied into annuals and perennials. Differences that occurred within the clades of perennial and annual species between gypsy- and copia-like retroelements indicated that these retrotransposons were differentially active during Helianthus speciation, suggesting that the evolution of the 2 retroelement families was, within limits, independent.     

Next generation sequencing reveals genome downsizing in allotetraploid Nicotiana tabacum, predominantly through the elimination of paternally derived repetitive DNAs

We used next generation sequencing to characterize and compare the genomes of the recently derived allotetraploid, Nicotiana tabacum (<200,000 years old), with its diploid progenitors, Nicotiana sylvestris (maternal, S-genome donor), and Nicotiana tomentosiformis (paternal, T-genome donor). Analysis of 14,634 repetitive DNA sequences in the genomes of the progenitor species and N. tabacum reveal all major types of retroelements found in angiosperms (genome proportions range between 17-22.5% and 2.3-3.5% for Ty3-gypsy elements and Ty1-copia elements, respectively). The diploid N. sylvestris genome exhibits evidence of recent bursts of sequence amplification and/or homogenization, whereas the genome of N. tomentosiformis lacks this signature and has considerably fewer homogenous repeats. In the derived allotetraploid N. tabacum, there is evidence of genome downsizing and sequences loss across most repeat types. This is particularly evident amongst the Ty3-gypsy retroelements in which all families identified are underrepresented in N. tabacum, as is 35S ribosomal DNA. Analysis of all repetitive DNA sequences indicates the T-genome of N. tabacum has experienced greater sequence loss than the S-genome, revealing preferential loss of paternally derived repetitive DNAs at a genome-wide level. Thus, the three genomes of N. sylvestris, N. tomentosiformis, and N. tabacum have experienced different evolutionary trajectories, with genomes that are dynamic, stable, and downsized, respectively.     

Sequence similarity based identification of abiotic stress responsive genes in chickpea

Chickpea (Cicer arietinum L.) is an important food legume crop, particularly for the arid regions including Indian subcontinent. Considering the detrimental effect of drought, temperature and salt stress on crop yield, efforts have been initiated in the direction of developing improved varieties and designing alternate strategies to sustain chickpea production in adverse environmental conditions. Identification of genes that confer abiotic stress tolerance in plants remains a challenge in contemporary plant breeding. The present study focused on the identification of abiotic stress responsive genes in chickpea based on sequence similarity approach exploiting known abiotic stress responsive genes from model crops or other plant species. Ten abiotic stress responsive genes identified in other plants were partially amplified from eight chickpea genotypes and their presence in chickpea was confirmed after sequencing the PCR products. These genes have been functionally validated and reported to play significant role in stress response in model plants like Arabidopsis, rice and other legume crops. Chickpea EST sequences available at NCBI EST database were used for the identification of abiotic stress responsive genes. A total of 8,536 unique coding long sequences were used for identification of chickpea homologues of these abiotic stress responsive genes by sequence similarity search (BLASTN and BLASTX). These genes can be further explored towards achieving the goal of developing superior chickpea varieties providing improved yields under stress conditions using modern molecular breeding approaches.     

裸燕麦Ty1-copia类反转录转座子反转录酶序列的分离、鉴定与分析

本研究根据Ty1-copia类反转录转座子反转录酶的保守区设计简并引物,通过PCR扩增,从裸燕麦(Avena nuda L.)品种‘品燕1号’基因组中分离获得23条Ty1-copia类反转录转座子序列,并对序列特征、系统发育关系及其转录活性进行分析。结果显示,23条Ty1-copia类反转录转座子存在较高的异质性,序列间的一致性为45%～98%,存在插入、移码和终止密码突变,但频率不高;系统发育分析结果表明,燕麦Ty1-copia类反转录转座子在进化过程中主要为垂直传递。本研究通过检索燕麦基因表达数据库,发现了5个有转录活性的Ty1-copia类反转录转座子。     

植物反转录转座子及其在功能基因组学中的应用

高等植物中的反转录转座子是构成植物基因组的重要成分之一.它分病毒家族和非病毒家族两类,病毒家族包括反转录病毒和类似于反转录病毒的非病毒转座子,病毒家族中的反转录转座子可再细分为Ty3-gypsy类和Ty1-copia类;非病毒家族可细分为LINE类和SINE类.正常情况下大部分反转录转座子不具有活性,某些生物或非生物因素胁迫可激活部分反转录转座子转座.反转录转座子自身编码反转录酶进行转录,以"拷贝-粘贴"的转座模式导致基因组扩增和进化.具有活性的反转录转座子通过插入产生新的突变,可作为一种基因标签技术,应用于功能基因组学研究,并成为研究植物基因功能和表达的重要技术平台.本文综述了近几年来在植物反转录转座子方面的研究进展,主要包括植物反转录转座子的结构、特征、活性及其对基因组的影响和它们在功能基因组学中的应用.