The Effect Of Trichoderma Asperellum T6 On Plant-growth Promoting Under P-deficiency And The Role Of Its Siderphores On Colonization

Phosphorus is one of the important elements for plants growth and development,but the content of soluble phosphorus in soil is rare,which is difficult to meet the needs of plants growth.The beneficial microorganisms in soil can transform the insoluble phosphorus into the soluble phosphorus by producing enzymes or organic acids,which can be absorbed and utilized to promote the growth and development of plants directly.However,there are many mechanisms of promoting plant growth under low phosphorus stress,in which the effective colonization of microorganisms in the rhizosphere is also a significant factor.Trichoderma asperellum T6,a biocontrol and growth promotion fungus was isolated and identified from plant rhizosphere by our laboratory,which can resistant to biotic and abiotic stresses.Previous studies showed that Trichoderma asperellum could promote plant growth under the condition of low phosphorus and iron stress,but its mechanism was not clear.The relationship of the secondary metabolite siderophores of Trichoderma asperellum under low iron stress and the colonization of bacteria in plant rhizosphere under low phosphorus stress has not been studied.In this paper,T6 was used to study the effects of different phosphorus concentrations on the growth of Arabidopsis thaliana,the IAA production,phosphorus solubilization,siderophore production and the colonization in Arabidopsis thaliana roots.The effects of low phosphorus stress on the expression of siderophore gene and auxin gene of Trichoderma asperellum was analyzed.The colonization of the T6,T6-1 and ?sidA in Arabidopsis thaliana root,serving the functions of the relationship betweensiderophores and the colonization were identified.The effects of Trichoderma asperellum on auxin expression of Arabidopsis and siderophores on rhizosphere colonization under p-deficiency was studied firstly,which provides a theoretical basis for the plant-growth promoting mechanism of Trichoderma asperellum.The specific research are summarized as follows:(1)The effects of Trichoderma asperellum T6 on seed germination,root length and fresh weight of Arabidopsis thaliana under P-deficiency were studied.The results showed that the germination rate,root length and fresh weight of Arabidopsis thaliana inoculated with Trichoderma asperellum were significantly higher than those without T6 under P-deficiency,but there was no significant difference in the fresh weight of Arabidopsis under sufficient-P condition,which proved Trichoderma asperellum can promote the growth of Arabidopsis thaliana under P-deficiency.(2)The effects of different phosphorus concentration on the production of siderophores,IAA and the ability of dissolving phosphorus of T6 were determined.Trichoderma asperellum,which was screened by rifampicin labeling method,was used to study the colonization in Arabidopsis rhizosphere.The results showed that there was no significant difference in IAA yield and phosphorus solubilizing ability of Trichoderma asperellum under different phosphorus concentrations,but low phosphorus stress promoted the yield of siderophores.The rhizosphere colonization of Trichoderma asperellum under low phosphorus stress was 2.5~3 times higher than that under sufficient phosphorus stress,which indicated that low phosphorus stress promoted the rhizosphere colonization of Trichoderma asperellum.(3)RT-PCR and Q-PCR were used to study the effect of low phosphorus stress on the expression of siderophore gene sidA of Trichoderma asperellum.The results showed that low phosphorus stress can promote the expression of sidA.It can also increase the secretion of fluorescence intensity(auxin)in the root of DR5:: GFP and promote the expression of auxin gene YUC in Arabidopsis thaliana.(4)Compared with T6,T6-1(obtained by UV mutagenesis)and ?sidA(obtained and preserved by our laboratory)decreased their siderophore production significantly,but there was no significant difference in IAA production and phosphorus solubilizing ability.Under low phosphorus stress,there was no significant difference of the colonization of the three strains in the iron-containing medium(without siderophores),but the colonization of T6-1 and ?sidA was significantly lower than that of the T6 in the iron-deficient medium(with siderophores),which showed that siderophores could promote the rhizosphere colonization of Trichoderma asperellum.