Symposium IV: Evolution of Plant Development
Abs #
40001: Evolution of plant body plan from Physcomitrella to Arabidopsis
Green plants landed more than 450 million years ago, and the basic body plan of land plants, the shoot system composed of a stem and leaves, was established in their early stage of evolution. To trace the origin and evolution of the molecular mechanisms of shoot system, homologues of the SHOOTMERISTEM LESS (STM) gene, which is a major regulator of shoot initiation and maintenance in flowering plants, were characterized in the fern Ceratopteris richardii and the moss Physcomitrella patens in addition to the assessment of polar auxin transport in the moss. Basic functions of STM and polar auxin transport are preserved among their diploid generation, although the moss does not form shoot-like structure in its diploid generation. This suggests that basal genetic tools for shoot system were established in the shoot-less common ancestor of land plants. On the other hand, STM expression and polar auxin transport were not detected in the haploid leafy-shoots of the moss, suggesting that diploid shoot systems of the vascular plants and haploid shoot systems of the moss evolved in parallel with different molecular mechanisms and that diploid shoots evolved with a de novo developmental system in stead of recruiting preexisted haploid shoot system.
The flower is a reproductive organ of angiosperms. MADS-box genes mainly manage the development. We characterized MADS-box genes in the moss Physcomitrella and three charophycean green algae. These genes were specifically expressed in eggs and sperm during their differentiation, and the expression. These suggest that land plant MADS-box genes were originally involved in the differentiation of haploid reproductive cells, and then such haploid genes were recruited into a diploid generation. To assess whether MADS-box genes with such ancestral functions maintained in higher plants, expression analyses of 107 Arabidopsis MADS-box genes were performed. This revealed that several MADS-box genes are expressed in pollen with generative cells and likely maintain their original functions.
We constructed an EST database of the moss Physcomitrella including 15,883 putative transcripts. The comparison between haploid-dominant moss transcriptome and the diploid-dominant Arabidopsis genome showed a general similarity between them. Based on these results, a scenario on the evolution of haploid and diploid body plans in land plants will be discussed.
