Impact Of Bt Cotton On Functional Gene Expression And Metabolic Enzyme Activity Of AM Fungi

Arbuscular mycorrhizal(AM) fungi are ubiquitous soil microorganisms in almost all kinds of soil ecosystems. AM fungi can form mutualistic symbioses with 80% of terrestrial plant families, facilitating the uptake of water and mineral nutrients, such as phosphate and nitrogen, to their host plants. And in return, AM fungi receive carbohydrates from the host. It has been proved that the nutrient exchange in the plant-fungi interface occurs in periarbuscular membrane. This are realized by the gene expression of a series of transporters and the catalysis of metabolic enzymes. Among those genes and enzymes, phosphate transporter gene, alkaline phosphatase gene, monosaccharide transporter gene, and phosphatase, urease play an important role in this process.AM fungi are sensitive to the change of plant physiological and biochemical characterics. In this study, we investigated the symbiotic relationships of AM fungus R.irregularis with five pairs of Bt cotton and their corresponding non-Bt lines. Mycorrhizal symbiosis structure, the expression of AM fungal genes, enzyme activities and symbiotic effect were detected at different time points. The main results are as follows:(1) The transformation of Bt gene resulted in a significant alteration on mycorrhizal colonization. The colonization rate, infection intensity, and arbuscular abundance of Bt cotton lines were lower than their corresponding non-Bt lines, except Zhong 41. Compared with the non-Bt lines, arbuscular area of Jin 26, Jin 44 and GK12 was significantly smaller, but there was no significant differences between Bt lines Zhong 41, sGK 321 and their corresponding non-Bt lines.(2) The transformation of Bt gene had a significant effect on the expression of GintPT, GintALP and GintMST2 gene of R.irregularis. Except some time points, the expression level of GintPT, GintALP, GintMST2 in Jin 44, Jin26, Zhong41 were lower than their corresponding non-Bt lines; the expression level of three genes in GK12 had no significant differences in contrast with Si3; the expression level of three genes in sGK321 was higher than that in Shiyuan321.(3) The transformation of Bt gene had an impact on the activity of alkaline phosphatase(ALP), acid phosphatase(ACP) and urease(URE). Except GK12, the activity of ALP, ACP and URE in Bt cotton roots decresed significantly or decreased without significant difference in contrast with those in non-transgenic lines.(4) The transformation of Bt gene had no significant impact on symbiotic effect. Inoculation with R.irregularis significantly increased the plant biomass and phosphate concentration, but the transformation of Bt gene did not result in significant difference in the biomass and phosphate concentration. Both inoculation with R.irregularis and the transformation of Bt gene did not lead to remarked difference in nitrogen concentration.