γ-Tubulin interacts with E2F transcription factors to regulate proliferation and endocycling in Arabidopsis

gamma-Tubulin is associated with microtubule nucleation, but evidence is accumulating in eukaryotes that it also functions in nuclear processes and in cell division control independently of its canonical role. We found that in Arabidopsis thaliana, gamma-tubulin interacts specifically with E2FA, E2FB, and E2FC transcription factors both in vitro and in vivo. The interaction of gamma-tubulin with the E2Fs is not reduced in the presence of their dimerization partners (DPs) and, in agreement, we found that gamma-tubulin interaction with E2Fs does not require the dimerization domain. gamma-Tubulin associates with the promoters of E2F-regulated cell cycle genes in an E2F-dependent manner, probably in complex with the E2F-DP heterodimer. The up-regulation of E2F target genes PCNA, ORC2, CDKB1;1, and CCS52A under gamma-tubulin silencing suggests a repressive function for gamma-tubulin at G(1)/S and G(2)/M transitions, and the endocycle, which is consistent with an excess of cell division in some cells and enhanced endoreduplication in others in the shoot and young leaves of gamma-tubulin RNAi plants. Altogether, our data show ternary interaction of gamma-tubulin with the E2F-DP heterodimer and suggest a repressive role for gamma-tubulin with E2Fs in controlling mitotic activity and endoreduplication during plant development.