Genetic Basis Of High-molecular-weight Glutenin Subunit Variation In Wheat-rye Hybrid

Wide hybridization is an important way for speciation and an important force in plant evolution. Wide hybrid can generate novel traits, some of them can be inherited to the offspring. It plays as, therefore, a contributor of genetic diversity. Although wide hybridization and allopolyploidization have been largely studied, little is known about the molecular mechanism of generating novel traits.High-molecular-weight glutenin subunit (HMW-GS) affects quality and its structure associates with processing quality of wheat flour. In this study, we study the HMW-GS variations in hybrids of common wheat Shinchunaga (Triticum aestivum L.,2n=42, AABBDD) with Qinling rye (Secale cereale L. cv. Qinling,2n=14, RR) by analysis of morphology, cytology and molecular biology. Our results contribute to understand the molecular mechanism of HMW-GS variations. The results are as follows:SDS-PAGE analysis found three types of HMW-GS variations in F4seeds:(1)1Bx7, lBy8and1Dx2.2disappeared, while a new HMW-GS appeared neraby Rx in seeds B-1-2-2;(2)1Bx7,1By8disappeared in B-1-2-4;(3)1Bx7and1By8disappeared while a new HMW-GS nearby Rx in B-1-2-6. The HMW-GSs were consistent in their F5seeds derived from B-1-2-2and B-1-2-4, while F5seeds from B-1-2-6separated into the three types again. We further traced the composition of HMW-GS in their F1(B) and F2(B-1) and found them being wild type. However, F3(B-1-2) showed the muatant type.The two F5lines with homogenous HMW-GSs showed normal seed-sets and consistent agronomic traits that were similar to the maternal donor Shinchunaga. However, they were significant differences in plant height, tiller number, main spike length and spikelet number of main tiller from its paternal donor Qinling rye.Cytology analysis indicated all the F5hybrids having42chromosomes. At meiotic metaphase I (MI), they were paired into20ring and1rod bivalents, thus indicating a stable cytology. Further GISH analysis revealed that they had2rye chromosomes, which uaually formed a rod bivalent at MI and normally separated. FISH analysis indicated that they were1B/1R substitution line. These explained the reason of disappearance of1Bx7and1By8.Compared to wild type of Glu-1Dx2.2, we found a new gene sequence, named Glu-1Dx2.2v, with intact open reading frame of2523bp length that conatined typical HMW-GS structure and a deletion of two direct repeat sequences of295bp in the central repetitive region by illegitimated recombination. The generation of Glu-1Dx2.2v was the result of DNA deletion. In prokaryotic expression, the electrophoretic mobility for expression protein and the new HMW-GS are similar, thus confirmed that the new HMW-GS Glu-1Dx2.2v. The new Glu-1Dx2.2v expressed in endosperm. Our results proved that the new HMW-GS nearby Rx is the Glu-1Dx2.2vWe further traced the variation time of Glu-1Dx2.v and found that it may appeared in meiosis of F2generation by means of illegitimate recombination. At this stage, the union of a variation gamete and a wild gamete produced a F3seed that descended to later generations.