Crown gall
tumors are formed mainly by actions of a group of genes in the
T-DNA that is transferred from Agrobacterium tumefaciens and integrated into the nuclear
DNA of host plants. These genes encode
enzymes for biosynthesis of
auxin and
cytokinin in plant cells. Gene 6b in the
T-DNA affects
tumor morphology and this gene alone is able to induce small
tumors on certain plant species. In addition, unorganized calli are induced from leaf disks of tobacco that are incubated on
phytohormone-free media; shooty
teratomas, and morphologically abnormal plants, which might be due to enhanced competence of cell division and meristematic states, are regenerated from the calli. Thus, the 6b gene appears to stimulate a reprogramming process in plants. To uncover mechanisms behind this process, various approaches including the yeast-two-hybrid system have been exploited and
histone H3 was identified as one of the
proteins that interact with 6b. It has been also demonstrated that 6b acts as a
histone H3 chaperon in vitro and affects the expression of various genes related to cell division competence and the maintenance of meristematic states. We discuss current views on a role of 6b
protein in
tumorigenesis and reprogramming in plants.