Molecular Mechanism Of Grain Enlargement For Aegilops Tauschii-wheat Introgression Line KF21

Wheat(Triticum aestivum,2n=6x=42,AABBDD)is one of the most important crops in the world,and its yield has always been focused by the researchers.With hybridization and doubling of cultivated emmer wheat(T.dicoccum,2n=4x=28,AABB)and Aegilops tauschii(2n=14,DD),the common wheat is cultivated.Scince the genetic diversity of the subgenome D was much lower than the subgenomes A and B,the improvement of common wheat faced the bottleneck.To increase the genetic diversity of the subgenome D is urgently needed.At present,distant hybridization is the dominant way to introduce excellent exogenous genes into common wheat.Aegilops tauschii,which is the D genome ancestor of common wheat,contains plenty of high resistant and yield genes,which are important genetic resources for variety improvement.In our previous study,an introgression line of Aegilops tauschii-wheat was obtained by hybridization of Zhoumai 18 and Aegilops tauschii,and back with Zhoumai 18,and then selfing 8times.The grain size and weight of the introgression line KF21,was significantly higher than that of the recurrent parent Zhoumai 18 in 5 consecutive years.But the molecular mechanism of grain enlargement is still unclear.In this study,we used Aegilops tauschii-wheat introgression line KF21 and recurrent parent Zhoumai 18 to reveal the molecular mechanism of grain enlargement of KF21 by morphological,cytological and genomic methods.The main results are as follows:(1)The characteristics of the introgression line KF21.Observation and statistics of the phenotypic traits of the introgressive line KF21 showed similarity to Aegilops tauschii on seedling phenotype and spike type,the stem is purplish red,the cob is longer,and the spikelet shell isharder,which is obviously different from wheat.Resequencing analysis showed that the D genome of KF21 had the most introgression genes with of 2465 introgression genes totally.And the chromosome 5D has the most introgression genes.The karyotype identification exhibited that there were 42 chromosomes in KF21,including 14 A,B,and D groups for each.Among them,a pair of 1BL/1RS chromosomes from control parent Zhoumai18 were also found.These results indicate that KF21 is a real and stable introgression line.(2)Comparison of grain phenotypes between the introgression line KF21 and Zhoumai 18.100 uniform mature grains were used to analyze grain length,grain width,circumference,area and100-kernel weight..The results showed that the difference between the other traits of KF21 and Zhoumai 18 was significant except grain width(P <0.05).The average grain length and 100-grain weight of KF21 grains are 7.76 mm and 5.98 g,respectively,which is higher than these of Zhoumai 18,and its yield is obviously increased.The grain length,grain width and fresh weight of KF21 and Zhoumai 18 were measured and compared everyday after flowering and pollination.During the period of 7 days to 10 days,the both growth rate was faster with 2.43 mm increasing for KF21 and 2.14 mm for Zhoumai 18,respectively.and the grain morphology almost stoped chaning at 12 days post pollination.However,the nutrients continue to accumulate with the weight increasing.(3)In order to explore the molecular mechanism of controlling the grain size for introgressive line KF21,16 samples including the pericarp,seed coat and endosperm of KF21 and its control parents Zhoumai18 at 8 days,10 days and 11 days post pollination were sequenced.233.26 Gb of transcriptome data was obtained,.Results showed that differentially expressed genes are mainly distributed in groups B and D,with fewer genes in group A.There are more differentiallyexpressed genes in the pericarp and seed coat,but fewer in the endosperm.The proportion of differentially expressed genes is biggest in the 11-day tissues.A total of 3922 significantly enriched entries were found by Gene ontology analysis,which were mainly divided into two groups: biological process and molecular function,containing 86 and 41 subcategories,respectively.A total of 1345 differentially expressed genes including16 metabolic pathways categories were annotated by KEGG pathway analysis.(4)According to the reported auxin signaling pathway of Arabidopsis thaliana,homologous genes of related genes in wheat were identified.The expression levels of some key auxin signaling pathway genes in the introgression line KF21 were significantly higher than those in Zhoumai 18.The tryptophan synthase in the tryptophan synthesis pathway of IAA precursor is TSA/TSB.The homologous gene expression of TSA reached the maximum value of 27.56 in KF21 10-day pericarp,and the maximum difference in 8-days endosperm was 27 times.The expression trend of TSB homologous gene increased gradually,reaching a maximum of 47.52 in the 11-day pericarp.The homologous gene of the aminotransferase AMI1 in the indole-3-pyruvic acid(IPy A)pathway reached a maximum expression level of 9.98 in the 10-day pericarp,while the expression level was lower in Zhoumai 18 at different stages.The two homologous genes of the amidase AMI1 in the indole-3-acetamide(IAM)pathway in wheat,their expression levels reached the maximum in the 11-day pericarp,12.85 and 10.32,respectively.The expression patterns of jasmonic acid and gibberellin signal pathway related genes in KF21 and Zhoumai 18 are similar,and the difference is not significant.The above results showed that the expression pattern of auxin homologous genes in wheat is basically consistent with the phenomenon of grain enlargement of KF21,indicating that auxin plays an important role in the grains development.