Study On Allelic Variations Of The Key Starch Synthesis Gene TaSS?b-D In Wheat (Triticum Aestivum L.)

Transient starch provides carbon and energy for plant growth,and its synthesis is regulated by the joint action of a series of enzymes.SSIV is one of the important starch synthase isoforms,but its impact on wheat starch synthesis has not yet been reported due to the lack of mutant lines.TILLING technology was used to find out point mutations in M₂ population for TaSSIVb-D in wheat cultivar Jing 411.Based on the previous research,we detected whether these point mutations can inherit in M₅ population or not.Two mutations?nonsense and missense?in line E054-13 and E1137showed stable expression and significant phenotypic results in all generations.Expression analysis was studied in wheat leaves and grains during different developing stages of the three homeologous TaSS?b genes of these mutated lines.The main purpose of study was to estimate the effect of TaSS?b-D point mutations on expression and the function of SSIV in wheat.The main results were as following:1.Ten point mutations of wheat TaSSIVb-D gene had been detected,and among them one nonsense?E054-13?,one splicing?E2-2-558?and three missense?E469,E1137,E1226?mutations were inherited in M₅ population but five other point mutations were segregated in this population which showed that these mutations had no genetic effect on TaSSIVb-D.2.The expression analysis of the three homeologous TaSS?b genes showed that this gene was mainly expressed in the leaves of TaSS?b-D,while TaSS?b-A was less expressed.There was no difference in TaSS?b-A and TaSS?b-B at seedling stage,elongation stage and heading stage of wheat during expression analysis comparative to wild type.The overall results showed that point mutation led to reduce the expression of TaSSIVb-D,such as E054-13 showed 1/5 less expression from wild type in every stage of plant,while E1137 had significant difference at seedling stage.3.The three homeologous TaSS?b genes had different expression pattern in different developmental stages of grain.In wild type,TaSS?b-A expressed lowest in 18 day,however TaSS?b-D and TaSS?b-B were in 12 day.TaSS?b-D expression became highest in 24 day,while TaSS?b-A and TaSS?b-B expressed highest in 6 day.However,the expression level of TaSS?b-D was significantly lower in mutants,but TaSS?b-A and TaSS?b-B were no change.4.Phenotypic analysis revealed that the number of starch granules reduced at every stage of mutant plant leaves.In the mutants,the number of chloroplasts containing 0-2 granules were significantly increased,while the number of chloroplasts containing 3-4 granules were decreased.These results indicate that TaSSIVb-D plays an important role in the formation of transient starch granules in wheat.5.The photosynthesis parameters of E054-13 showed significant difference from wild type at heading stage and chlorophyll contents were also significantly reduced at seedling stage,elongation stage and heading stage which showed that point mutation in TaSSIVb-D has indirect effect on photosynthesis process.