Radiation hybrid QTL mapping of Tdes2 involved in the first meiotic division of wheat

Abstract

Since the dawn of wheat cytogenetics, chromosome 3B has been known to harbor a gene(s) that, when removed, causes chromosome desynapsis and gametic sterility. The lack of natural genetic diversity for this gene(s) has prevented any attempt to fine map and further characterize it. Here, gamma radiation treatment was used to create artificial diversity for this locus. A total of 696 radiation hybrid lines were genotyped with a custom mini array of 140 DArT markers, selected to evenly span the whole 3B chromosome. The resulting map spanned 2,852 centi Ray with a calculated resolution of 0.384 Mb. Phenotyping for the occurrence of meiotic desynapsis was conducted by measuring the level of gametic sterility as seeds produced per spikelet and pollen viability at booting. Composite interval mapping revealed a single QTL with LOD of 16.2 and r (2) of 25.6 % between markers wmc326 and wPt-8983 on the long arm of chromosome 3B. By independent analysis, the location of the QTL was confirmed to be within the deletion bin 3BL7-0.63-1.00 and to correspond to a single gene located ~1.4 Mb away from wPt-8983. The meiotic behavior of lines lacking this gene was characterized cytogenetically to reveal striking similarities with mutants for the dy locus, located on the syntenic chromosome 3 of maize. This represents the first example to date of employing radiation hybrids for QTL analysis. The success achieved by this approach provides an ideal starting point for the final cloning of this interesting gene involved in meiosis of cereals.

High‐resolution mapping of the pericentromeric region on wheat chromosome arm 5AS harbouring the Fusarium head blight resistance QTLQfhs.ifa‐5A

“…Gamma radiation affects the entire genome causing homogeneous marker loss regardless of positions within the chromosomes (Bassi et al ., ; Riera‐Lizarazu et al ., ; Tiwari et al ., ). Accordingly, radiation‐induced breaks were found to be evenly distributed across the 5AS chromosome, agreeing with previous RH mapping results (Balcárková et al ., ; Bassi et al ., , ; Kalavacharla et al ., ; Kumar et al ., ; 2105; Mazaheri et al ., ; Tiwari et al ., , ). We calculated a 389‐fold increased map resolution for the low‐recombinogenic Qfhs.ifa‐5A interval compared to the genetic map and an 817.5‐ and 633‐fold for the centromeric and interstitial bin, respectively.…”

Fast‐forward genetics by radiation hybrids to saturate the locus regulating nuclear–cytoplasmic compatibility in Triticum

“…The in vivo RH strategy has been documented in wheat to provide high map resolution (reviewed in Kumar et al ., , , b; Bassi et al ., ). Here, the resolution achieved was 288 Kb, which is fivefold higher than what previously reported by Michalak et al ., (1.5 Mb) using a population 3.5 times smaller.…”

“…Further, this resolution is similar to what reported by Bassi et al . (), where a resolution of 388 Kb was achieved for chromosome 3B using a population of 696 RH individuals tagged with 140 markers. Overall, this is the highest map resolution reported to date for RH in wheat, confirming the advantages of this approach for mapping its complex genome.…”

A High Resolution Radiation Hybrid Map of Wheat Chromosome 4A

“…However, none of them matches the map constructed in this study in the density and the resolution. There are two RH maps developed for wheat chromosome 3B based on seed panels and either combination of ISBP, SSR and DArT markers on 70 RH lines (Kumar et al, 2012a), or DArT markers on 463 RH lines (Bassi et al, 2013). The first map, with the length of 1871 cR comprises 541 markers.…”