Cytogenetically Engineered Rye Chromosomes 1R to Improve Bread-making Quality of Hexaploid Triticale

Hexaploid triticale (X Triticosecale Wittmack) is rarely used for human consumption because of its poor bread-making quality. To create the genetic potential for bread-making quality similar to that of bread wheat (Triticum aestivum L), rye (Secale cereale L.) chromosome 1R in triticale cv. Presto was cytogenetically engineered to remove secalin loci Sec-1 and Sec-3, and to introduce wheat storage protein loci Gli-1 and Glu-1. The manipulations were by homoeologous recombination between rye chromosome 1R and 1B or 1D of wheat, followed by homologous recombination of primary recombinants with translocation breakpoints in desired locations. This approach generated three classes of multi-breakpoint translocation chromosomes named Valdy, FC and RM. Chromosome Valdy is a three breakpoint translocation with loci Gli-D1, Sec-1 and Glu-D1; chromosomes FC1 and FC2 are five breakpoint translocations with loci Gli-D1 and Glu-D1, and chromosomes RM are six breakpoint translocations with loci Gli-B1 and Glu-D1. Preliminary tests of the effects of these chromosomes show a 230 to 250% increase of the SDSsedimentation value over the recipient triticale Presto. While the impact of these chromosomes on the agronomic value of triticale is not clear, they restore to triticale the genetic load of gluten-encoding loci similar to that of bread wheat, thereby creating the genetic potential for breeding bread-making triticales. T A MAN-MADE HYBRID of wheat (Triticum spp.) and rye was created to combine the high yielding capacity of wheat with the stress tolerance of rye. Early efforts concentrated on octoploids generated from bread wheat and rye, but their inherent meiotic instability prevented breeding progress. Only hexaploid triticales, mostly the so-called secondary triticales selected from hybrids of octoploids with newly-synthesized hexaploids, have truly demonstrated triticale’s promise. Despite its high yielding capacity and presumed lower nutrient and soil requirements than wheat, triticale’s acreage worldwide has been increasing only slowly (Arseniuk and Oleksiak, 2002). This may be a consequence of its rather limited end uses (Briggs, 1991; Pena, 1996). Triticale is bred and produced mainly for animal feed and forage. Despite some early attempts in several countries, it has never gained status as a human food. This is largely because, by wheat standards, its breadmaking quality is poor. Good quality baked products can be obtained from triticale but by using different baking technologies (Rakowska and Haber, 1991). The bread-making quality of bread wheat is determined by several factors of which the quantity and quality of gluten-forming storage proteins is critical (Bietz, 1987). Gluten is formed on dough mixing by polymerization of shorter subunits into long chains and interactions with lipids, giving dough its strength and elasticity (Simmonds, 1981). In bread wheat, gluten-forming proteins are encoded by loci located on chromosomes of homoeologous groups 1 and 6 (Payne et al., 1984; Payne, 1987). In group 1 the long arms carry lociGlu-1 for high molecular weight glutenin subunits; the short arms have loci Gli-1 for gliadins and Glu-3 for low molecular glutenin subunits. In group 6 the short arms carry loci Gli-2 that encode gliadins. The number of active genes in each locus may range from zero to many; the exact number of active gliadin genes has not yet been determined (Anderson et al., 1997). Each class of storage proteins contributes to a specific dough characteristic, such as strength, elasticity, extensibility and so on, that, in combination, determines loaf characteristics. Storage proteins in rye are known as secalins, and loci controlling them are located in positions corresponding to those of wheat (Shewry et al., 1984). Chromosome 1R has a Sec-1 locus on its short arm that encodes alcoholextractable proteins similar to gliadins of wheat; the long arm has locus Sec-3 in a position corresponding to the Glu-1 loci of wheat. TheGli-2-related rye locus, Sec-2, is located on the short arm of chromosome 2R. This is because of an ancient chromosome translocation, 2R–6R that differentiates wheat from rye (Devos et al., 1993). Rye cannot be baked using wheat bread-making technology. Because introgressions of rye chromatin in commercial wheats are frequent, the effect of secalins on the bread-making quality of wheat should be well known. It is generally believed to be detrimental, but this belief may be valid only for the Sec-1 locus (Kumlay et al., 2003). As all introgressions of Sec-1 into wheat have been accompanied by concomitant removal of one set of Gli-1/Glu-3 loci, it is not clear whether it is the presence of Sec-1 or the absence of wheat loci that negatively impact the bread-making quality. Not all secalins are detrimental to bread-making quality: replacement of some Glu-1 wheat loci by the Sec-3 locus produced a small positive effect on dough parameters in bread wheat (Kumlay et al., 2003), and in all rankings of the relative contribution of individual group-1 chromosomes to bread-making quality of triticale, rye chromosome 1R has always placed higher than wheat chromosome 1A (Kazman and Lelley, 1996; Lukaszewski, 1996, 1998;Wos et al., 2002; Kumlay et al., 2003). No effect of Sec-2 on any parameters of wheat dough has so far been detected (Gupta et al., 1989). The genomic constitution of hexaploid triticale is AABBRR whereas in bread wheat it is AABBDD. In effect, in triticale the rye (R) genome replaces the D genome of bread wheat. This difference in genomic constiDep. of Botany and Plant Sciences, Univ. of California, Riverside, CA 92521. Received 1 Mar. 2006. *Corresponding author (adam. [email protected]). Published in Crop Sci. 46:2183–2194 (2006). Crop Breeding & Genetics doi:10.2135/cropsci2006.03.0135 a Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 2183 Published online September 8, 2006