Transcriptomics of bryophyte apical cells and young sporophytes

Alternation of generations, in which the haploid and diploid stages of the life cycle are each represented by multicellular forms that differ in their morphology, is a defining feature of the land plants (embryophytes). Anciently derived lineages of embryophytes grow predominately in the haploid gametophytic generation from shoot apical meristems (SAMs) that give rise to photosynthetic structures with either leaf-like organs or a ribbon-like thallus. More recently evolved plant lineages have multicellular SAMs, and photosynthetic shoot development is restricted to the sporophyte generation. The molecular genetic basis for this evolutionary shift from gametophyte dominant to sporophyte dominant life cycles remains a major question in the study of land plant evolution. We used laser microdissection and next generation RNA sequencing to address whether angiosperm meristem patterning genes expressed in the sporophytic SAM of Zea mays are expressed in the gametophytic SAMs, or in the non-meristematic sporophytes, of the model bryophytes Marchantia polymorpha and Physcomitrella patens.