Epidermal fate map of the Arabidopsis shoot meristem.

The shoot meristem generates all of the aerial structures of an adult plant. It is organized in three layers which produce the epidermis (L1 layer) and the subepidermal layers (L2 and L3). The origin of adult structures has previously been fate mapped to the primary meristem for L2 and L3 tissues. In this work we constructed a fate map of L1 cells in the embryonic shoot meristem. Using the trichome mutation stichel as an epidermal marker, we analyzed 153 plants that included 178 sectors. Sectors on early leaves were found to be smaller and occurred more frequently than those on late leaves. Sectors on late leaves also appeared often to affect more than one leaf. In general, the width and extent of sectors were found to be variable rather than cell lineage-restricted. Our analysis allowed us to assign the most likely fates of L1 precursor cells within the embryonic shoot meristem. The results suggest that the meristem integrates growth dynamics and patterning of all three tissues. In contrast to this coordinated growth behavior of meristematic cells, we found a difference in the lineage restrictions between the L1 and the L2 for the formation of axillary buds.