Differentiation of programmed Arabidopsis cells.

Plants express genes that encode enzymes that catalyse reactions to form plant secondary metabolites in specific cell types. However, the mechanisms of how plants decide their cellular metabolic fate and how cells diversify and specialise their specific secondary metabolites remains largely unknown. Additionally, whether and how an established metabolic program impacts genome- wide reprogramming of plant gene expression is unclear. We recently isolated PAP1-programmed anthocyaninproducing (red) and -free (white) cells from Arabidopsis thaliana; our previous studies have indicated that the PAP1 expression level is similar between these two different cell types. Transcriptional analysis showed that the red cells contain the TTG1-GL3/TT8-PAP1 regulatory complex, which controls anthocyanin biosynthesis; in contrast, the white cells and the wild-type cells lack this entire complex. These data indicate that different regulatory programming underlies the different metabolic states of these cells. In addition, our previous transcriptomic comparison indicated that there is a clear difference in the gene expression profiles of the red and wild-type cells, which is probably a consequence of cellspecific reprogramming. Based on these observations, in this report we discuss the potential mechanisms that underlie the programming and reprogramming of gene expression involved in anthocyanin biosynthesis.