Genetic Map Of Triticum Turgidum Based On A Hexaploid Wheat Population Without Genetic Recombination For D Genome And SDG8, FT Function Synergistically To Regulate Plant Architecture And Flowering Time

In a previous study, we constructed a synthesizing double haploid (SynDH) hexaploid wheat population, which is actually tetraploidization-hexaploid DH population since they contain recombinant A and B chromosomes of two different T. turgidum genotypes while all the D chromosomes from Ae. tauschii are homogenous across the whole population. The present paper reports the development of a genetic map using this population. The major findings are:1. Of the606markers used to assemble the genetic map,588(97%) were assigned to linkage groups. They included513DArT (Diversity Arrays Technology) markers,72simple sequence repeats (SSR), one insertion site-based polymorphism (ISBP), and two high-molecular-weight glutenin subunit (HMW-GS) markers. This map has a length of2048.79cM and an average distance of3.48cM between adjacent markers.2. Compared with previously reported maps, most of shared markers showed highly consistent orders, indicating that this SynDH population is valid in generating genetic map.3. This map was successfully used to identify five quantitative trait loci (QTL), including two for spikelet number on chromosomes7A and5B, two for spike length on7A and3B, and one for1000-grain weight on4B.4. On the other hand, differences in crossability QTL between the two T. turgidum parents could be responsible for the existence of segregation distortion regions on chromosomes1A,3B, and6B.The Arabidopsis SET domain group8(SDG8) is a histone H3methyltransferase. It involves in a series of important plant development processes including flowering, branching and the control of seed specific gene expression. In this study, a mapping population was established from a suppressor mutant of sdg8-2. A new single point substitutional mutant allele of FT, which was named ft-11hereafter, was cloned via traditional map based cloning. Based on the characterization study of the double mutant on flowering time, plant architecture and seed storage protein expression, it was found that FT and SDG8function synergistically to regulate flowering time and plant archtecure, but FT did not involve in the regulation of seed specific gene expression. The major findings are:1. A single point mutant in FT can suppress the early flowering phenotype resulted from sdg8mutation:The flowering time was determined in wild type, single mutant sdg8-2,ft-1,ft-10and double mutant ft-11sdg8-2plants, by means of both dates and rosette leaf numbers. The flowering time of double mutant plants was in between that of sdg8and ft single mutant plants, similar to that of the wild type plants. This suggested that ft-11can suppress the early flowering phenotype of sdg8-2mutant plants. Based on realtime PCR analysis, FLC transcript level was reduced, while the API expression was at a low level when the SOC1expression was increased. This indicated that the reduction of the inhibitor FLC level may promote the expression of downstream API.2. Single amino aicd substitution at the key residues of the FT protein will greatly affect its function:Constructs expressing mutant version of FT proteins were constructed by targeted mutagenesis on several key amino acid residues. The physical associations between FT, including wild type and all mutant versions, and FD or14-3-3proteins were evaluated using BiFC and Y2H. It was found that the different FT mutant proteins showed altered binding capability to FD or14-3-3proteins, which was in line with the observed morphological phenotypes of the plants.3. A single point mutant in FT can suppress the more branch phenotype resulted from sdg8mutation:The branch number of the ft-11sdg8-2double mutant was less than that of sdg8-2single mutant, but still more than that of wild type or ft single mutant plants. RT-PCR and realtime PCR analysis demonstrated that the expressions of a few key regulatory genes on branch were altered in the double mutant. SPS1expression was increased in the double mutant compared to that of sdg8-2, while the UGT74E2expressopn was lower. These results indicated that the ft-11mutant resulted in altered auxin/cytokinin balance, therefore suppressed the more branch phenotype of sdg8.4. Mutation in FT did not affect the expression of seed specific genes:A pCG::GUS reporter system was introduced into the ft-11sdg8-2plants to determine the expression of seed specific genes. ft-11mutation did not affect the expression of seed storage proteins. RT-PCR analysis demonstrated that At2S2and At7S1were not expressed in wild type, but in sdg8-2and the double mutant. The expression levels of these genes were similar in sdg8-2and the double mutant.