Single-stranded DNA of 5'-upstream region of the rolC gene interacts with nuclear proteins of carrot cell cultures

The Agrobacterium Phenotypic Plasticity (Plast) Genes

The transfer of T-DNA sequences from Agrobacterium to plant cells is a well-understood process of natural genetic engineering. The expression of T-DNA genes in plants leads to tumors, hairy roots, or transgenic plants. The transformed cells multiply and synthesize small molecules, called opines, used by Agrobacteria for their growth. Several T-DNA genes stimulate or influence plant growth. Among these, iaaH and iaaM encode proteins involved in auxin synthesis, whereas ipt encodes a protein involved in cytokinin synthesis. Growth can also be induced or modified by other T-DNA genes, collectively called plast genes (for phenotypic plasticity). The plast genes are defined by their common ancestry and are mostly found on T-DNAs. They can influence plant growth in different ways, but the molecular basis of their morphogenetic activity remains largely unclear. Only some plast genes, such as 6b, rolB, rolC, and orf13, have been studied in detail. Plast genes have a significant potential for applied research and may be used to modify the growth of crop plants. In this review, I summarize the most important findings and models from 30 years of plast gene research and propose some outlooks for the future.

Pattern of DNA binding of nuclear proteins to the proximal Agrobacterium rhizogenes rolC promoter is altered during somatic embryogenesis of carrot

Carrot cells cultured in vitro in a medium supplemented with 2,4-D (2,4-dichlorophenoxyacetic acid) proliferate as unorganized cell clusters. Upon removal of 2,4-D from the culture medium, these cells undergo somatic embryo formation through globular, heart, and torpedo stages. Since the proximal -255 bp upstream region of the rolC gene of the Ri plasmid confers somatic embryogenesis-related activation on the uidA gene in transgenic carrot cell culture, we investigated the interaction of nuclear proteins with the proximal -255bp upstream sequences to characterize the mechanism of somatic embryogenesis-related activation. Gel retardation experiments revealed that there were several different profiles of the relative levels of DNA binding activities in nuclear protein extracts from calli, PEMs (proembryogenic masses), globular embryos, and heart/torpedo embryos. The binding activity associated with a fragment (-203 bp to -92 bp) of one protein (BI) was most abundant in globular embryos. Another DNA binding protein (AII) showed the highest DNA binding activity in calli, but had low binding activities in PEMs and globular embryos. Such an altered pattern of DNA binding activities of nuclear proteins may contribute to somatic embryogenesis-related activation of the rolC promoter. Competition experiments with oligonucleotides revealed that the BI protein interacts with AT-rich sequences.

A 43-kDa nuclear tobacco protein interacts with a specific single-stranded DNA sequence from the 5'-upstream region of the Agrobacterium rhizogenes rolC gene

We identified in the nuclear extract of tobacco seedlings a 43-kDa DNA-binding protein RCS2 that interacted with the 5'-upstream region of the rolC gene of the Agrobacterium rhizogenes Ri plasmid. DNA-protein gel shift and competition assays demonstrated that RCS2 bound to single-stranded DNA in a sequence-specific manner. A five-base direct repeat is important for the DNA binding of RCS2. South-Western blot analysis was employed to determine the size of RCS2 which appears to be approx. 43 kDa.