Study On The Mechanism Of Blueberry Root Hair Loss And Its Adaptive Mechanism

Blueberry(Vaccinium spp.),as a perennial shrub or small shrub species,belongs to Ericaceae family.Because of the high anthocyanins content and the medicinal functions of blueberry,FAO had listed blueberry as one of five international human health foods.Lacking root hair,blueberry's shallow fibrous root systems mainly distributes in shallow soil.Therefore,the soil's physico-chemical properties,such as soil compaction,organic matter content as well as the mycorrhiza status have a greater impact on its growth than other fruit species and the symbiotic mycorrhiza is of special importance.However,few report was available to unveil its mechanisms.So,based on the observation on the development process of blueberry root,the molecular mechanism of root hair loss in blueberry was analyzed through gene cloning and expression pattern assay.Meanwhile,The effects of soil microbe on the growth of blueberry were evaluated by comparing the tissue-cultured plantlets of blueberries grown in sterilized and non-sterilized soil.Finally,mycorrhizal fungi that have a positive effect on the growth of blueberries was screened and identified,which aimed to obtain the beneficial strains and establish a suitable vaccination methods.The study would supply a reference for the functions of mycorrhizal fungi for blueberry and promote the development of blueberry.The main results were summarized as followingThe roots of the two-year-old 'Brigitta' were used as the experimental material,the primary mechanism of lacking root hair in blueberry were analyzed through cloning the expression pattern assay of the relative genes.The results showed the root hair growth related genes WER,TTG and GL2 were successfully amplified from the blueberry root cDNA,but CPC,ETC1 and TRY failed to be cloned.Structural analysis indicated that the proteins encoded by WER,TTG and GL2 had the same domains as their homologies in other plant species.The amino sequences of GL2,WER were closest similar to the homologies in grape,indicating the similar protein functions.Since the CPC,ETC1 and TRY were not expressed,and WER,TTG and GL2 were normally expressed,it was speculated that the blueberry lacking root hair was resulted from the functions of the WER combined with TTG/GL3-EGL3 complex which are positively regulated the expression of GL2,thus inhibiting the development of root hair.The sterile blueberry tissue-cultured plantlets(Brigitta)were used as the experimental material.The effects of rhizosphere microbe on the growth of blueberry were studied through comparing the seedlings grown in sterilized and non-sterilized soils.The results showed that the growth of blueberries,especially the aboveground,in the non-steriled soil was significantly higher than that grown in the sterile soil.But the number of rhizospheric bacteria and fungi were lower than that in sterilized soil.The number of bacteria was especially difference.The sterilization of soil also increased the number of fungi,however,more symbiotic fungi were observed in roots grown in non-steriled soils,which may resulted from the predominance of the beneficial microbe.Furthermore,the activity of sucrase and hydrogen peroxide in non-sterilized rhizospheric soil were 0.56 and 2.15 times higher than that of the sterilized soils,respectively.The symbiotic fungi in root fractionation of 5-year-old blueberry(Brigitta,Premier,Sharpblue)were cultured,purified and identified through ITS sequence.Endophytic fungi strains with the number of 9,9 and 8 were respectively isolated from the roots of Brigitta,Premier and Sharpblue.The sequence results showed that these strains isolated from the same blueberry cultivars shared the same or the similar ITS sequence despite the significantly different morphological characteristics.Such as B1209(Talaromyces aculeatus)and B1210(Talaromyces verruculosus),T1205/T1213/T1214(Helotiales sp.)and T1206(Helotiales sp.)were the different sprecies but belonged to the same genus.Strain T1205,T1213 and T1214 belonged to Helotiales sp.(AB847035.1),and X1206,X1209 belonged to Epacris microphylla root associated fungus(AY 268189.1).Meanwhile,the mycorrhizal fungi of different blueberry roots were also the same.Such as B1207,T1209,X1206 and X1209 were belonged to Epacris microphylla root associated fungus(AY268189.1).B1205 and X1205 were belonged to Thozetella sp.(JX244056.1).X1207,T1205,T1213 and T1214 were belonged to Helotiales sp.(AB847035.1).Then,the tissue-cultured plantlets were inoculated with the isolated strains.After 2 month growth,it was found that B1206(Uncultured Ascomycota)increased the highest biomass growth.In summary,blueberry lacking root hair was resulted from the non-detectable transcription levels of CPC,ETC1 and TRY,as well as the normal expressions of WER,TTG and GL2,but the related regulatory mechanism still need further study.The growth of blueberry seedlings in non-sterilized soils was higher than that insterilized soils,implying that rhizospheric microbe being of great importance in the growth of blueberries.The symbiotic fungi isolated from roots of different blueberry cultivars diversified but shared some common species,simultaneously.After inoculation trials,it was showed B1202 and B1206 increased the highest biomass growth of blueberry seedlings.