Cell specific, cross-species expression of myrosinases in Brassica napus, Arabidopsis thaliana and Nicotiana tabacum.

A prototypical characteristic of the Brassicaceae is the presence of the myrosinase-glucosinolate system. Myrosinase, the only known S-glycosidase in plants, degrades glucosinolates, thereby initiating the formation of isothiocyanates, nitriles and other reactive products with biological activities. We have used myrosinase gene promoters from Brassica napus and Arabidopsis thaliana fused to the beta -glucuronidase (GUS) reporter gene and introduced into Arabidopsis thaliana, Brassica napus and/or Nicotiana tabacum plants to compare and determine the cell types expressing the myrosinase genes and the GUS expression regulated by these promoters. The A. thaliana TGG1 promoter directs expression to guard cells and phloem myrosin cell idioblasts of transgenic A. thaliana plants. Expression from the same promoter construct in transgenic tobacco plants lacking the myrosinase enzyme system also directs expression to guard cells. The B. napus Myr1.Bn1 promoter directs a cell specific expression to idioblast myrosin cells of immature and mature seeds and myrosin cells of phloem of B. napus. In A. thaliana the B. napus promoter directs expression to guard cells similar to the expression pattern of TGG1. The Myr1.Bn1 signal peptide targets the gene product to the reticular myrosin grains of myrosin cells. Our results indicate that myrosinase gene promoters from Brassicaceae direct cell, organ and developmental specific expression in B. napus, A. thaliana and N. tabacum.