Expression of bean arcelin-1 and β-phaseolin genes in seeds of common bean and transgenic tobacco

Abstract

A gene, PHVARC1-1, encoding the insecticidal protein arcelin-1 has been isolated from the common bean (Phaseolus vulgaris, line SARCl-7). It contains no intron and is 2692 bp long, including 1167 bp in the 5' upstream region, 798 bp in the coding region, and 727 bp in the 3' downstream region. The coding region of PHVARC1-1 is identical to those of pARC1-11, (Osborn et al, 1988b) and Phvarc1a (Anthony et al, 1991). Arcelin and phaseolin are the major seed storage protein in domestic beans. The expression of these genes has been compared at the mRNA and transcriptional levels in the common bean plants (Phaseolus vulgaris). Northern blot analysis revealed that the onset of arcelin mRNA accumulation coincides with a reduction in the phaseolin mRNA level. This reduction at least partly due to a decrease in the transcription rate of phaseolin genes, as shown by nuclear run-on assays. Potential gene interaction mechanisms are discussed. The expression of these two genes was also examined in transgenic tobacco plants. The arcelin and/or phaseolin gene(s) under the control of their respective or alternative promoters were introduced into tobacco (Nicotiana tabacum cv Xanthi.nc) via the Agrobacterium/Ti plasmid vector system. All of these transgenes were expressed in the transformed tobacco seeds. The accumulation of the phaseolin mRNA in the developing tobacco seeds peaked about 2 days earlier than the arcelin mRNA. However, the changes at the mRNA level observed for the two genes in the common beans were not observed in the transgenic tobacco plants. The levels of arcelin mRNA driven by either promoter were lower than those of the phaseolin mRNA. The possible causes of this finding are discussed.