Application of AtMYB75 as a reporter gene in the study of symbiosis between tomato and Funneliformis mosseae.

Composite plants containing transgenic hairy roots produced with Agrobacterium rhizogenes-mediated transformation have become an important method to study the interaction between plants and arbuscular mycorrhizal fungi (AMF). Not all hairy roots induced by A. rhizogenes are transgenic, however, which leads to requirement of a binary vector to carry a reporter gene to distinguish transgenic roots from non-transformed hairy roots. The beta-glucuronidase gene (GUS) and fluorescent protein gene often are used as reporter markers in the process of hairy root transformation, but they require expensive chemical reagents or imaging equipment. Alternatively, AtMYB75, an R2R3 MYB transcription factor from Arabidopsis thaliana, recently has been used as a reporter gene in hairy root transformation in some leguminous plants and can cause anthocyanin accumulation in transgenic hairy roots. Whether AtMYB75 can be used as a reporter gene in the hairy roots of tomato and if the anthocyanins accumulating in the roots will affect AMF colonization, however, are still unknown. In this study, the one-step cutting method was used for tomato hairy root transformation by A.rhizogenes. It is faster and has a higher transformation efficiency than the conventional method. AtMYB75 was used as a reporter gene in tomato hairy root transformation. The results showed that the overexpression of AtMYB75 caused anthocyanin accumulation in the transformed hairy roots. Anthocyanin accumulation in the transgenic hairy roots did not affect their colonization by the arbuscular mycorrhizal fungus, Funneliformis mosseae strain BGC NM04A, and there was no difference in the expression of the AMF colonization marker gene SlPT4 in AtMYB75 transgenic roots and wild-type roots. Hence, AtMYB75 can be used as a reporter gene in tomato hairy root transformation and in the study of symbiosis between tomato and AMF.