Genomes, Chromosomes and Genes of the Wheatgrass Genus Thinopyrum: the Value of their Transfer into Wheat for Gains in Cytogenomic Knowledge and Sustainable Breeding

Abstract

Perennial wheatgrass species of the genus Thinopyrum possess several appealing attributes for wheat improvement, contributing to tolerance to biotic and abiotic stresses, as well as to quality and even to yield increase. Major genes or QTLs underlying such traits have been identified on numerous chromosomes of both diploid (Th. elongatum and Th. bessarabicum) and polyploid (mainly Th. intermedium and Th. ponticum) representatives of the genus, having different genome origin (E, J, St/S) and involving several homoeologous groups. Thinopyrum chromosomes sharing homoeology with wheat group 7 chromosomes turned to be particularly rich in beneficial genes; among them, a Th. ponticum group 7 chromosome referred to as 7Ag or 7el has been extensively targeted in various successful attempts of harnessing its attractive gene content. A survey of the several wheat translocation/recombinant lines involving this chromosome in the background of both bread and durum wheat is given. Such lines are described as highly valuable tools for a variety of studies, from development of integrated genetic and physical maps, to the analysis of structural and functional characteristics associated with defined alien chromosome subregions. The validity of Th. ponticum group 7 transfers as breeding materials (notable genes and traits including Lr19, Sr25, Fusarium head blight resistance, yellow pigment content, and even yield) is also highlighted. Finally, examples are given of pyramiding of group 7 Thinopyrum genes through 'precision' breeding strategies of chromosome

Harnessing Genetic Diversity of Wild Gene Pools to Enhance Wheat Crop Production and Sustainability: Challenges and Opportunities

“…ponticum largely homologous 7el 1 L and 7el 2 L chromosome arms, both contain one or more Sd genes, which have been studied rather intensively, primarily because of the linked beneficial genes of breeding relevance (see above in this section, and Section 2). The SD phenotype determined by Sd gene(s)/SDR(s) that is linked to the 7el 1 L segment of translocation line T4 and of other bread and durum wheat lines possessing the same or shorter 7el 1 L portions, exemplifies the highly variable, probably background-dependent, outcomes, as described earlier (reviewed in [36]). On the other hand, the effects of the 7el 2 L-linked Sd gene(s) appear relatively more consistent through studies and backgrounds.…”

“…As shown in Figure 5, the work of Forte et al [41] enabled a higher map resolution than previously achieved [64], separating this SDR from a more proximal one, containing the PSR129 marker, associated, in turn, to 7el 1 L-linked SD effects in various studies and materials (both bread and durum wheat recombinant lines, see [36] for a review). Within the 7el 2 L SDR, it seems of interest to note the presence of a wheat EST (Expressed Sequence Tag), namely BF200943, for whose nucleotide sequence a BLAST search (https://blast.ncbi.nlm.nih.gov/Blast.cgi) indicated a high homology with a protein product belonging to the mitogen-activated protein kinase (MAPK) cascades of several Triticeae species.…”

“…Various beneficial genes can thus be accumulated, and unwanted genes possibly eliminated. Particularly noteworthy examples of this strategy concern gene combinations from perennial Triticeae species of the Thinopyrum genus, one of the richest sources of valuable genes/QTL for wheat improvement [36,37]. By means of ph1b-mediated recombination between a bread wheat-Th.…”

“…In progeny of wheat-alien combinations, one of the most likely causes for the skewed transmission of complete or segmental alien chromosomes of various wild species (most studied those from Aegilops and Thinopyrum genera) has been suggested to be gametophytic competition during zygote formation, with male gametogenesis being affected in the majority, though not all of the cases [36,54,55]. The phenomenon, however, proved to be highly variable even for a given SDR containing a segregation distortion (Sd) gene, going from selective or even exclusive retention in the wheat background through generations (preferential transmission), to a more or less dramatic self-elimination.…”

“…However, when considering that such genes are widely spread, if not omnipresent, in plants, in which they must have played a major evolutionary role in terms of karyotype diversification and speciation by sexual isolation, it seems reasonable to expect a variety of elements and mechanisms responsible for these phenotypes between and within species [36,55,65]. In this frame, epigenetic phenomena should also be contemplated.…”