Cyclin A participates in the TSO1-MYB3R1 regulatory module to maintain shoot meristem size and fertility in Arabidopsis.

The stem cell pools at the shoot apex and root tip give rise to all the above- and below-ground tissues of a plant. Previous studies in Arabidopsis identified a TSO1-MYB3R1 transcriptional module that controls the number and size of the stem cell pools at the shoot apex and root tip. As TSO1 and MYB3R1 are homologous to components of an animal cell cycle regulatory complex, DREAM, Arabidopsis mutants of TSO1 and MYB3R1 provide valuable tools for investigations into the link between cell cycle regulation and stem cell maintenance in plants. In this study, an Arabidopsis cyclin A gene, CYCA3;4, was identified as a member of the TSO1-MYB3R1 regulatory module and cyca3;4 mutations suppressed the tso1-1 mutant phenotype specifically in the shoot. The work reveals how the TSO1-MYB3R1 module is integrated with the cell cycle machinery to control cell division at the shoot meristem.