The Relationship Of Differential Gene Expression To Root Hair Length Variation Of Diploid And Allopolyploid Wheats

Polyploidization has taken place throughout approximately 70%of angiosperms,which has long been recognized as a driving force shaping the evolution of flowering plants.Common wheat is a typical allohexaploid which has prominent performance such as increased productivity,greater quality,or even broader adaptability to stressful environments compared to diploid and tetraploid progenitors.However,little is known about the consequence of hybridization and polyploidization on root hair length in wheat and the underlying molecular mechanisms by which polyploids contribute to the phenotypic variation is still ambiguous.In this thesis,the relationship between differential gene expression pattern and root hair length variation in diploid and allopolyploid wheats were characterized and the main results were summarized as follows:1.We found that the root hair length of synthetic allotetraploid wheat was significantly longer than that of diploid parents,but no difference was observed between synthetic allohexaploid and allotetraploid parent,suggesting the contribution of D-genome to root hair length was limited.2.We compared the root hair length of 109 natural wheat accessions with varying ploidy and found 1)the root hair length of SS group was significantly longer than that of AA and DD groups;2)the root hair length of tetaploid was significantly longer than that of AA,SS and DD groups;3)allopolyploid wheats displayed increased root hair length when compared to three diploid progenitors but no statistical difference in root hair length between the allohexaploid and allotetraploid wheat,indicating increased root hair length in allohexaploid wheat originated in the allotetraploid progenitors and retained during subsequent evolution.3.We cloned wheat ortholog to AtRHD6 and AtRSL4 which are related to root hair development in Arabidopsis.The expression level of TaRHD6 and TaRSL4 genes were up-regulated in three synthetic allotetraploid wheats compared to their diploid parents.Further investigation showed that there were significantly positive correlation(P<0.01)between root hair length and expression level of TaRHD6 and TaRSL4 in 50 natural wheat accessions with varying ploidy.Overexpression of TaRHD6 and TaRSL4 in Arabidopsis showed longer root hair length and increased shoot fresh biomass compared to wild type.Remarkably,the differences of aerial size between transgenic line and wild type were more obvious under nutrient-poor conditions.4.We noted that unequal expression of TaRSL4 homoeologs is prevalent in allopolyploid wheat.Moreover,wheat transgenic line with constitutive expression of TaRSL4 increased shoot fresh biomass under nutrient-poor conditions compared to wild type.Remarkably,synthetic allotetraploid wheat displayed much higher mid-parent heterosis of shoot fresh biomass under nutrient-poor conditions compared to nutrient-rich conditions.Taken together,increased root hair length profoundly enhanced the capacity to absorb nutrients and improved wheat seedling growth.5.We performed RNA-Seq on two-day-old seedlings roots of both wheat transgenic lines of TaRSL4 and wild type.In total,we identified 2,095 differentially expressed genes between each other,among which up-regulated and down-regulated genes in transgenic lines were 1,673 and 422,repectively.In addition,we found that TaMRHl was up-regulated in transgenic lines,and interestingly,the expression level of TaRSL4 and TaMRH1 genes were significantly correlated with each other(P<0.05)and a significant correlation(P<0.01)was observed between the expression level of TaMRH1 and root hair length in 50 natural wheat accessions with varying ploidy,indicating TaMRHl might be a candidate downstream gene of TaRSL4.6.DNA interference inhibited the expression of TaRHD6 and TaRSL4 in the wheat roots,resulting the decreased root hair length.We also cloned wheat gene TaEXPBl that is orthologous to HvEXPB1 related to root hair development in barley.We also verified that down-regulation of TaEXPBl gene in roots inhibited root hair growth by using DNAi,indicating DNAi technique may facilitate functional analysis of gene associated with root hair development in wheat.In addition,TaEXPBl gene displayed high-parent expression pattern in three synthetic allotetraploids and was up-regulated in transgenic wheat of TaRSL4 compared to wild type.Conclusively,we proposed that up-regulation of TaRHD6 and TaRSL4 as well as their downstream genes TaMRH1 and TaEXPB1 was one of the principle molecular variables contributing to the increased root hair length in synthetic allotetraploid wheat.