Root‐specific expression of opine genes and opine accumulation in some cultivars of the naturally occurring genetically modified organism Nicotiana tabacum

Summary Previous studies have shown that Nicotiana tabacum contains three Agrobacterium ‐derived T‐ DNA sequences inherited from its paternal ancestor Nicotiana tomentosiformis . Among these, the TB locus carries an intact mannopine synthase 2′ gene ( TB ‐ mas2 ′). This gene is similar to the Agrobacterium rhizogenes A4‐ mas2 ′ gene that encodes the synthesis of the Amadori compound deoxyfructosyl‐glutamine ( DFG or santhopine). In this study we show that TB ‐ mas2 ′ is expressed at very low levels in N. tomentosiformis and in most N. tabacum cultivars; however, some cultivars show high TB ‐ mas2 ′ expression levels. The TB ‐ mas2 ′ promoter sequences of low‐ and high‐expressing cultivars are identical. The low/high level of expression segregates as a single Mendelian factor in a cross between a low‐ and a high‐expression cultivar. pTB ‐mas2 ′ ‐ GUS and pA 4‐mas2 ′ ‐ GUS reporter genes were stably introduced in N. benthamiana . Both were mainly expressed in the root expansion zone and leaf vasculature. Roots of tobacco cultivars with high TB ‐ mas2 ′ expression contain detectable levels of DFG .