| Castanea henryi is not only an important woody grain tree species in southern China,but also an important precious timber tree species.Forestry production is closely related to mycorrhiza,and hormones,especially auxin,play an important role in mycorrhizal development and even plant growth and development.Studies have shown that the inoculation of ectomycorrhizal(ECM)fungi can significantly promote lateral root growth of C.henryi,and the auxin precursor indole-3-butyric acid(IBA)can also induce lateral root development of C.henryi.Therefore,does IBA play a regulatory role in the establishment of ECM symbiotes in host plants of C.henryi?Therefore,the following experiments were carried out in this study:(1)We screened the strains not affected by IBA and the optimum concentration of IBA to promote the development of lateral roots of C.henryi.(2)The seedlings of C.henryi were inoculated with ECM fungi and treated with exogenous IBA.The effects of IBA on mycorrhizal development and seedling growth of C.henryi seedlings were determined by measuring mycorrhizal infection rate,growth index,root configuration,photosynthesis parameters,nutrient content,organic matter metabolism content,auxin-related enzyme activity and endogenous hormone content.(3)Based on the whole genome data of C.henryi,the genes related to mycorrhizal symbiosis and auxin signal transduction were screened,and the expression characteristics of IBA on genes related to symbiosis and auxin signal transduction pathway were clarified by qRT-PCR analysis,in order to explore the mechanism of mycorrhizal development regulated by IBA.The main results are as follows:1.The strain not affected by IBA was identified as LY-9(Scleroderma citrinum),and the optimum concentration of IBA is 10 μM.Six ECM fungal strains obtained in the previous stage of the research group were cultured in the medium containing different concentrations of IBA(0 μM,0.1 μM,1 μM,10 μM,50 μM,100 μM),and the colony diameter and mycelial dry mass were determined.The results showed that except LY-9,the other five strains were affected by the concentration of IBA.The colony diameter and mycelial dry mass of LY-9 were 1.4 cm and 1.6 cm,respectively.The seedlings of C.henryi were placed in the medium with different concentrations of IBA,and the number of lateral roots and root configuration were counted.The results showed that when the concentration of IBA was 10 μM,the root configuration was normal and the number of lateral roots reached 45.2.Both inoculation and IBA treatment can significantly improve the seedling growth and nutrient content of C.henryi,and the effect of inoculation with IBA(JJ+IBA)was the best.After six months of inoculation,the plant height and ground diameter increased by 33%and 15%compared with the control(CK)treatment,respectively.JJ+IBA significantly promoted the growth of root tip number of C.henryi seedlings.After six months of inoculation,the root tip number reached 7413,which was significantly higher than that of other treatments and increased by 68%compared with CK treatment.Compared with the total nitrogen and total potassium content,the inoculation treatment had the most significant effect on the total phosphorus content of C.henryi.The total phosphorus content of JJ+IBA treatment was the highest,and the total phosphorus content of root,stem and leaf reached 2.21mg/g,0.90mg/g and 1.41mg/g,which was 2.94,1.76 and 2.04 times higher than that of the control treatment,respectively.3.Inoculation and IBA treatment significantly improved the physiological activity of C.henryi seedlings.After inoculation for six months,the inoculation treatment significantly decreased the contents of malondialdehyde,soluble sugar and abscisic acid in C.henryi seedlings.It increased the content of soluble protein,activities of auxin-related enzymes(peroxidase,polyphenol oxidase and indole acetic acid oxidase)and auxin content.After six months of inoculation,the root auxin content of C.henryi treated with JJ and JJ+IBA increased by 11%and 12%respectively,while the abscisic acid content decreased by 29%and 35%,respectively.4.IBA may be involved in mycorrhizal formation of C.henryi by regulating ChNORK gene.Eighteen genes related to mycorrhizal symbiosis and auxin signal transduction pathway were screened according to the whole genome of C.henryi.Fluorescence quantitative analysis of root tips of C.henryi seedlings with different treatments showed that the relative expression of mycorrhizal symbiosis related gene Che020397(ChNORK)in inoculated treatment(JJ)and inoculated with IBA treatment(JJ+IBA)was significantly higher than that of the control,and the expression of JJ+IBA treatment was the highest,which was 4.7 times higher than that of the control treatment.The expression of auxin-related genes Che003007(ChSA UR23)and Che022104(ChPODC)genes was significantly up-regulated in IB A treatment and inoculation treatment,and the expression of ChSAUR23 gene in IB A treatment(CK+IBA)and JJ treatment was 27 times and 60 times higher than that of control treatment,respectively. |
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