Differential expression of a gamma-zein gene in Medicago sativa, Lotus corniculatus and Nicotiana tabacum

With the aim of increasing the content of sulphur amino acids (SAAs) in the aerial part of the plants, Nicotiana tabacum and two leguminous species, Medicago sativa and Lotus corniculatus, were transformed with a maize gamma-zein gene (G1L), coding for a SAAs-rich protein. Gene fusions with two different promoters were constructed; one promoter was the constitutive cauliflower mosaic virus (CaMV) 35S and the other was the light-regulated ribulose bisphosphate carboxylase small subunit (rbcS) from a tobacco gene. The constructs were introduced by Agrobacterium-mediated gene transfer. All the transformants produced the G1L RNA (two differently sized transcripts were detected) and no relevant differences were found between the two promoters. Despite the presence of G1L message the gamma-zein was found only in tobacco plants (up to 0.05% of the alcohol soluble proteins). Post-transcriptional mechanisms seemed to inhibit protein accumulation. The low level of G1L RNA in the transformed plants was probably the main factor that limited the production of gamma-zein protein.