Abstract
Nicotine, a major alkaloid in tobacco plants, acts as a defensive compound against insects. Nicotine is produced in tobacco roots and transported to leaves for storage. We found that expression of two genes (NtMATE1, NtMATE2) was specifically suppressed in the nic1nic2 mutant root. These genes encode similar proteins, which are homologous to multidrug and toxic compound extrusion (MATE) family transporters. Expression of these genes was tightly controlled by NIC regulatory genes and observed specifically in the wild type root. Promoter::GUS expression analysis demonstrated that NtMATE1 was expressed all tissues except for epidermis in the differentiated region. In NtMATE1 over-expressing transgenic tobacco BY-2 cells, NtMATE1 was localized to the tonoplast. Analysis of nicotine secretion in NtMATE1 over-expressing BY-2 cells and transgenic tobacco roots in which NtMATE1 expression was reduced by RNAi suggest NtMATE1 promotes excretion of nicotine from the vacuole, and consequently facilitates translocation of nicotine from roots to aerial parts.
