γ-Tubulin interacts with E2FA, E2FB and E2FC transcription factors, regulates proliferation and endocycle in Arabidopsis

Abstract

Abstract γ-Tubulin is associated with microtubule nucleation, but evidence is accumulating in eukaryotes that it functions also in nuclear processes and in cell division control that are independent of its canonical role. We found that in Arabidopsis thaliana γ-tubulin interacts specifically with E2FA, E2FB, and E2FC transcription factors both in vitro and in vivo. The interaction of γ-tubulin with the E2Fs is not reduced in the presence of the dimerization partners (DPs) and, in agreement, we found that γ-tubulin interaction with E2Fs does not require the dimerization domain. γ-Tubulin associates with the promoters of E2F-regulated cell cycle genes in an E2F dependent manner, likely in complex with the E2F/DP heterodimer. The upregulation of E2F targets; PCNA, ORC2, CDKB1;1 and CCS52A under γtubulin silencing suggests a repressive function for γ-tubulin at G1/S, G2/M and 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 γ-tubulin RNAi plants. Altogether, our data show ternary interaction of γ-tubulin with E2F/DP heterodimer and suggest a repressive role for γ-tubulin with E2Fs in controlling mitotic activity and endoreduplication during plant development.