A sustained CYCLINB1;1 and STM expression in the neoplastic tissues induced by Rhodococcus fascians on Arabidopsis underlies the persistence of the leafy gall structure

Abstract

Rhodococcus fascians is a gram-positive phytopathogen that infects a wide range of plant species. The actinomycete induces the formation of neoplastic growths, termed leafy galls, that consist of a gall body covered by small shoots of which the outgrowth is arrested due to an extreme form of apical dominance. In our previous work, we demonstrated that in the developing gall, auxin drives the transdifferentiation of parenchyma cells into vascular elements. In this work, with the use of transgenicArabidopsis thalianaplants carrying molecular reporters for cell division (pCYCB1;1:GUS) and meristematic activity (pSTM:GUS), we analyzed the fate of cells within the leafy gall. Our results indicate that the size of the gall body is determined by ongoing mitotic cell divisions as illustrated by strongCYCB1;1expression combined with thede novoformation of new meristematic areas triggered bySTMexpression. The shoot meristems that develop in the peripheral parts of the gall are originating from high ectopicSTMexpression. Altogether the presented data provide further insight into the cellular events that accompany the development of leafy galls in response toR. fasciansinfection.