Different functions of the histone acetyltransferase HAC1 gene traced in the model species Medicago truncatula, Lotus japonicus and Arabidopsis thaliana.

In eukaryotes, histone acetyltransferases regulate the acetylation of histones and transcription factors, affecting chromatin structural organization, transcriptional regulation, and gene activation. To assess the role of HAC1, a gene encoding for a histone acetyltransferase in Medicago truncatula, stable transgenic lines with modified HAC1 expression in the model plants M. truncatula, Lotus japonicus, and Arabidopsis thaliana were generated by Agrobacterium-mediated transformation and used for functional analyses. Histochemical, transcriptional, flow cytometric, and morphological analyses demonstrated the involvement of HAC1 in plant growth and development, responses to internal stimuli, and cell cycle progression. Expression patterns of a reporter gene encoding beta-glucuronidase (GUS) fused to the HAC1 promoter sequence were associated with young tissues comprised of actively dividing cells in different plant organs. The green fluorescent protein (GFP) signal, driven by the HAC1 promoter, was detected in the nuclei and cytoplasm of root cells. Transgenic lines with HAC1 overexpression and knockdown showed a wide range of phenotypic deviations and developmental abnormalities, which provided lines of evidence for the role of HAC1 in plant development. Synchronization of A. thaliana root tips in a line with HAC1 knockdown showed the involvement of this gene in the acetylation of two core histones during S phase of the plant cell cycle.