Transgenic tobacco plants expressing rgp1, a gene encoding a ras‐related GTP‐binding protein from rice, show distinct morphological characteristics¹

Abstract

SummaryThe rgp7 gene, originally isolated from rice seedlings, encodes a small GTP-binding protein which is related to the product of the human proto-oncogene, ras-p21. To determine the physiological role of the rgpl protein, rgpl-p25, the coding region of rgpl was introduced into tobacco plants in both sense and antisense orientations. Transformants, which were found to contain the rgpi gene at up to three loci, showed distinct phenotypic changes. The most notable was a reduction in apical dominance with increased tillering, together with dwarfism or abnormal flower development or both. These effects were similarly observed in both sense and antisense transformants. Northern hybridization analysis showed that rgp7 was expressed only in phenotypically abnormal transformants and not in the apparently normal phenotypes. Furthermore, the R1 progenies from most transformants co-segregated into a 31 ratio for both kanamycin resistance and tillering. The expression of tgp7, a presumed tobacco homologue of rgpl, was markedly reduced in transformants expressing the antisense rgpi, whereas it was apparently unaffected in transformants with sense rgpl. These observations suggest that the phenotypic changes in antisense transformants may be mediated by an effect on native tgp7 mRNA, whereas in sense transformants the changes may be induced by over-production of rgplp25. The possibility that the increased tillering may be related to abnormal phytohormone metabolism or response pathways, and that rgpl -p25 may mediate the transmission of signals in these pathways is discussed.

Developmental Abnormalities and Reduced Fruit Softening in Tomato Plants Expressing an Antisense Rab11 GTPase Gene

“…The rumpled leaves and abnormal flower morphology seen in tobacco plants expressing a NTH15 homeobox transgene was accompanied by reduced GA 1 levels and increased levels of cytokinin (Tamaoki et al, 1997), and plants with increased cytokinin levels caused by transformation with the Agrobacterium ipt gene form ectopic buds on leaves (Estruch et al, 1991). Increased levels of cytokinin and abnormal flower development were both seen in tobacco plants expressing sense or antisense copies of a rice Rab gene (Kamada et al, 1992;Sano et al, 1994). We have confirmed that ethylene levels were perturbed in our plants, suggesting that phytohormone levels may be involved in producing at least some of the phenotypic effects in plants expressing Rab antisense transgenes as well as in those expressing homeobox genes.…”

Expression of a rice homeobox gene causes altered morphology of transgenic plants.

“…The isopentenyl transferase gene of the Ti plasmid also induces formation of abundant shoot apices in transgenic plants (Smart et al, 1991;Smigocki, 1991;Hagen and Guilfoyle, 1992), as does the rolC gene in the Ri plasmid (Estruch et al, 1991) and the rice GTP binding protein gene (Kamada et al, 1992). Overproduction of cytokinins is thought to be the mechanism by which these genes increase the number of shoot apices and reduce apical dominance.…”

Rice Diversity Panel Mapping for Identifying Genetics Behind Leaf Vein Density Trait in Rice (<i>Oryza sativa</i> L.)

“…The rgp1 is a gene that encodes rasrelated GTP-binding protein. [29] reported that transgenic tobacco plants expressing rgp1, show different morphological characteristics. For example, some R1 progenies of selfpollinating plants developed abnormal leaf phenotypes, such as the abnormal branching of the main vein leading to the formation of twin or even triple leaves [29].…”