TRANSCRIPTIONAL ACTIVATION OF A MAIZE ALPHA-TUBULIN GENE IN MYCORRHIZAL MAIZE AND TRANSGENIC TOBACCO PLANTS

Mycorrhizae are symbioses between soil fungi and roots, with substanti al modifications of the cells of both partners. Thus, host cells colon ized by mycorrhizal fungi may express otherwise inactive genes. Here i t is demonstrated that two arbuscular mycorrhizal (AM) fungi, Glomus v ersiforme and Gigaspora margarita, cause the transcriptional activatio n of a gene coding for alpha-tubulin in the colonized cells of maize a nd transgenic tobacco roots. Tobacco plants transformed with a constru ct containing the maize Tub alpha 3 gene promoter fused upstream from the bacterial GUS gene showed an intense GUS activity only in meristem atic regions. When colonized by G. margarita, GUS activity was detecte d in the cortical root cells containing fungal arbuscules. No GUS acti vity was found in root cells when transformants carrying Tub alpha 1 p romoter were used, nor when Tub alpha 3 transformants were colonized b y ericoid mycorrhizal fungi, leading to a non-specific interaction. Ac tivation of the Tub alpha 3 appears to be specific to the gene and to the appropriate interaction. Further evidence that fully differentiate d host tissues re-activate the Tub alpha 3 gene following colonization by AM fungi also comes from accumulation of the corresponding transcr ipts in maize root cells containing arbuscules.