Mapping and survey sequencing of Dn resistance genes in Triticum aestivum L.

Bierman, Anandi (2015-03)

Thesis (PhD)--Stellenbosch University, 2015

Thesis

ENGLISH ABSTRACT : Diuraphis noxia Kurdjumov (Russian Wheat Aphid; RWA) is a pest of wheat and barley that has spread from its home range in the fertile crescent to most wheat producing countries except Australia. Since its first introduction to South Africa and the USA in the late 20th century, breeding programs for wheat phenotypes resistant to the aphid were put in place. Conventional breeding practices rely on phenotypic screening to verify traits carried by offspring and genetic tools such as marker assisted selection (MAS) have greatly aided this process in speed and accuracy. The size and complexity of the wheat genome, its allopolyploid nature and repetitive elements have, however, posed a challenge to studies on the genetics of this cereal crop. Many studies have focused on chromosome 3B which is the largest of the wheat chromosomes and easily separated from the redundant genomic background by techniques such as flow cytometry. The similarity in size of the remaining chromosomes however, limits the application of flow cytometry to their isolation. Databases such as Grain-Genes (http://wheat.pw.usda.gov/GG2/index.shtml) house marker data from various mapping studies for all wheat chromosomes and in 2014 the International Wheat Genome Sequencing Consortium (IWGSC) completed the draft genome sequence of wheat categorized by chromosome. Sources of resistance (Dn resistance genes) against RWA are located on chromosome 7D. but despite the marker and sequence data available currently, mapping studies specific for the Dn resistance genes are few. Additionally, sequence data available is derived from cultivars susceptible to RWA and is not comprehensively annotated and assembled in many cases. In this study, we demonstrate a novel, combined approach to isolate and characterize the Dn resistance genes through the use of a genetic map constructed from Amplified Fragment Length Polymorphism (AFLP), Expressed Sequence Tag (EST) and microsatellite markers and a physical map constructed from Next Generation Sequencing (NGS) data of ditelosomic chromosomes (7DS and 7DL) isolated by microdissection on the PALM microbeam system. A 122.8 cM genetic map was produced from 38 polymorphic AFLP markers and two ESTs with the microsatellite Xgwm111 as anchor to related genetic maps. Through comparison to maps available on GrainGenes the location of the Dn1 resistance gene was narrowed down to a deletion bin (7DS5-0.36-0.62) on the short arm of chromosome 7D with an AFLP marker (E-ACT/M-CTG_0270.84) mapping closely at 3.5 cM and two ESTs mapping at 15.3 cM and 15.9 cM from Dn1. Isolation of individual chromosome arms 7DS and 7DL using the PALM Microbeam system allowed sequencing of the chromosome without the redundancy of the remainder of the hexaploid genome. Through isolating the chromosome arms in this way, a >80-fold reduction in genome size was achieved as well as a major reduction in repetitive elements. Analysis of the sequencing data confirmed that 7DL is the physically shorter arm of the chromosome though it contains the majority of protein coding sequences.

AFRIKAANSE OPSOMMING : Diuraphis noxia Kurdjumov (Russiese koring-luis; RWA) is « pes wat op koring en gars voorkom. Die pes het vanaf sy tuiste in die midde Ooste na meeste koringproduserende lande behalwe Australië versprei. Sedert die eerste bekendstelling van RWA in Suid Afrika en die VSA in die vroeë 20ste eeu is teelprogramme ten gunste van koring lyne met weerstand teen RWA begin. Tradisionele teelprogramme maak op fisieise observasie van die fenotipe staat om te verifieer of plante in die nageslag die gewenste eienskap dra. Genetiese metodes soos merkerondersteunde seleksie (MAS) versnel hierdie selekteringsproses grootliks. Die grootte en kompleksiteit van die koring genoom asook die polyploïde en herhalende natuur daarvan is « groot hindernis vir genetiese studies van hierdie graangewas. Baie studies het op chromosoom 3B gefokus wat die grootste van die koring chromosome is en dus maklik vanaf die res van die oorbodige genomiese agtergond deur tegnieke soos vloeisitometrie geskei word. Die ooreenkoms in grootte tussen die res van die chromosome bemoeilik die toepassing van vloeisitometrie om hulle te isoleer. Databasisse soos GrainGenes (http://wheat.pw.usda.gov/GG2/index.shtml) bevat merker data vanaf verskeie karterings-studies vir al die chromosome en in 2014 het die "International Wheat Genome Sequencing Consortium"(IWGSC) die voorlopige basispaarvolgorde van die koring genoom bekendgestel, gekategoriseer volgens chromosoom. Weerstandsbronne (Dn weerstandsgene) teen RWA kom meestal op chromosoom 7D voor. Ten spyte van merker en basispaarvolgorde data tans beskikbaar is karterings-studies spesifiek tot die Dn gene skaars en basispaarvolgorde data is vanaf kultivars afkomstig wat nie weerstandbiedend teen RWA is nie en waarvan die annotasie en samestelling baie keer nie goed is nie. In hierdie studie demonstreer ons « nuwe, gekombineerde aanslag om die Dn weerstandsgene te isoleer en karakteriseer deur van « genetiese kaart opgestel met "Amplified Fragment Length Polymorphism"(AFLP), "Expressed Sequence Tag"(EST) en mikrosatelliet merkers asook « fisiese kaart saamgestel deur die volgende-generasiebasispaarvolgordebepaling van ditelosomiese chromosome (7DS en 7DL) geïsoleer deur mikrodisseksie met die "PALM Microbeam"sisteem gebruik te maak. « Genetiese kaart van 122.8 cM was met 38 polimorfiese AFLP merkers en twee EST merkers geskep. Die mikrosatelliet, Xgwm111, is ook ingesluit en het as anker vir verwante genetiese-kaarte gedien. Deur vergelyking met genetiese-kaarte op GrainGenes is die posisie van die Dn1 weerstandsgeen vernou na « delesie bin (7DS5-0.36-0.62) op die kort arm van chromosoom 7D met « AFLP merker (EACT/ M-CTG_0270.84) wat ongeveer 3.5 cM vanaf die geen karteer. Die twee EST merkers is 15.3 cM en 15.9 cM vanaf die geen gekarteer. Isolering van die individuele chromosoom arms, 7DS en 7DL, deur van die "PALM Microbeam"sisteem gebruik te maak het basispaarvolgordebepaling van die chromosoom toegelaat sonder die oortolligheid van die res van die hexaploïde genoom. Deur die chromosoom so te isoleer is « >80-maal verkleining in genoom grootte bereik insluitend « groot reduksie in herhalende elemente. Analise van die data vanaf basispaarvolgordebepaling het bevestig dat chromosoom 7D die fisiese kleiner chromosoom is maar dat dit die meerderheid van proteïn koderende basispaarvolgordes bevat.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96912
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