Evolution of Life Cycle in Land Plants

摘要

A complete life cycle of sexually reproducing eukaryotes consists of a diploid phase and a haploid phase. The relative length of either phase varies greatly among different lineages of eukaryotes. Under a recently reconstructed molecular phylogeny of streptophytes (charophyte algae and land plants), we examined the pattern of life cycle change in Characeae, liverworts, mosses, hornworts, lycophytes, monilophytes, and seed plants. We found that the life cycle of land plants had evolved in a direction of continuously expanding the diploid phase while reducing the haploid phase. In other words, evolution of land plants can be viewed as a series of events of delaying meiosis after fertiliza-tion and reducing mitosis after meiosis. Adaptive significance of this life cycle change will be dis-cussed, and molecular mechanisms underlying this life change will also be explored.