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Title: A radiation hybrid map of chromosome ID reveals synteny conservation at a wheat speciation locus.

item Michalak De Jimenez, M
item Bassi, F
item Ghavami, F
item Simons, K
item Dizon, R
item Setan, R
item Alnemer, L
item Denstin, A
item Dogramaci, Munevver
item Simkova, H
item Dolezel, J
item Seth, K
item Luo, M-c
item Dvorak, J
item Gu, Yong
item Kianian, S

Submitted to: Functional and Integrative Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2013
Publication Date: 3/12/2013
Citation: Michalak De Jimenez, M.K., Bassi, F.M., Ghavami, F.G., Simons, K., Dizon, R., Setan, R.I., Alnemer, L.M., Denstin, A.M., Dogramaci, M., Simkova, H., Dolezel, J., Seth, K., Luo, M., Dvorak, J., Gu, Y.Q., Kianian, S.F. 2013. Accelerated evolution of the mitochondrial genome in an alloplasmic line of durum wheat. Functional and Integrative Genomics. 13:19-32.

Interpretive Summary: The genetic information of wheat is located in the nuclear, mitochondrial and chloroplast genomes. A proper cross-talk between the three genomes, referred to as “nuclear-cytoplasmic interactions” (NCI), is very critical for breeding programs when integrating desirable traits from close relatives through interspecific crosses. The close relatives of wheat are a valuable source of resistance genes to various biotic and abiotic stresses which are needed to enhance wheat cultivars. Species cytoplasm-specific (scs) genes are some of the genes involved in the NCI in wheat. A lack of appropriate scs genes is a major obstacle in generating viable and vigorous plants from crosses between durum wheat and its wild relatives. It is than very important to identify the position of scs genes to be able to introduce them into wheat cultivars to ensure the compatible NCI in the interspecific hybrids. This study focused on locating one of the scs genes, originating from bread wheat. The location of the scs gene was narrowed down using radiation hybrid mapping, comparative genomics, and synteny analysis. The evolutionary significance of the scs genes and their role in the speciation of grasses was also described.

Technical Abstract: The species cytoplasm specific (scs) genes affect nuclear-cytoplasmic interactions in interspecific hybrids. A radiation hybrid (RH) mapping population of 188 individuals was employed to refine the location of the scsae locus of Tritcum aestivum chromosome 1D. ‘Wheat Zapper’, a comparative genomics tool, was used to predict synteny between wheat 1D, Oryza sativa, Brachypodium distachyon, and Sorghum bicolor. A total of 57 markers were developed based on synteny or literature and genotyped to produce a RH map spanning 205.2 cR. An elegant testcross methodology was devised for the phenotyping of RH progenies, and through forward genetic the scsae locus was pinpointed to a 1.1 Mb segment containing eight genes. Further, the high resolution provided by RH mapping, combined with chromosome-wise synteny analysis, located the ancestral point of fusion between the telomeric and centromeric repeats of two paleochromosomes that originated chromosome 1D. Also, it indicated that the centromere of this chromosome is likely the result of a neocentromerization event, rather than the conservation of an ancestral centromere as previously believed. Interestingly, the scs locus is located in close proximity to the point of paleofusion, but it is speculated that the evolutionary importance of this locus has prevented rearrangement in this otherwise very eventful region, as synteny in this fragment is surprisingly well conserved. The so called “Maan’s scs hypothesis” is here reviewed from this prospective to conclude that the scs genes might not have only directed the speciation of the Triticeae tribe, but possibly of all the Poaceae.