De novo cortical cell division triggered by the phytopathogen Rhodococcus fascians in tobacco

Plant growth, development, and morphology can be affected by several enviro nmental stimuli and by specific interactions with phytopathogens. In many c ases, plants respond to pathogenic stimuli by adapting their hormone levels . Here, the interaction between the phytopathogen Rhodococcus fascians and one of its host plants, tobacco, was analyzed phenotypically and molecularl y. To elucidate the basis of the cell division modulation and shoot primord ia initiation caused by R. fascians, tobacco plants were infected at leaf a xils and shoot apices, Adventitious meristems that gave rise to multiple-sh oot primordia (leafy galls) were formed. The use of a transgenic line carry ing the mitotic CycB1 promoter fused to the reporter gene coding for beta - glucuronidase from Escherichia coli (uidA), revealed that stem cortical cel ls were stimulated to divide in an initial phase of the leafy gall ontogene sis. Local cytokinin and auxin levels throughout the infection process as w ell as modulation of expression of the cell cycle regulator gene Nicta;CycD 3;2 are discussed.