The Oirgin And Evolution Of Seven Major Plant Hormone Signaling Pathways

The transition of plants from the aquatic lifestyle to a terrestrial lifestyle450millionyears ago is one of the most important events in the evolution of life, with far-reachingconsequences for the global ecosystem. Terrestrial environment is significantly different fromthe ocean environment, such as the temperature, the UV radiation and so on, so the first landplants need to change their developmental programs and morphology to adapt the newenvironment. The capacity for plants to adapt to myriad environmental stimuli is mediated byplant hormones which regulate virtually all aspects of development, physiology, andmetabolism. However, up to now, the origin and evolutionary modes of plant hormonesignalings remained obscure. Here, we use a comparative genomic, phylogenetic approachand protein structural domain analyses to show that if the genomes of land plants encode themachinery of auxin, abscisic acid, cytokinin, gibberellin, ethylene, jasmonate acid andbrassinosteroid signaling pathways. The main results as follows:1. Cytokinin signaling pathway emerged before the emergence of green algae. Auxin,abscisic acid, cytokinin, gibberellin, ethylene and jasmonate acid signaling pathway emergedbefore plant colonized land. Brassinosteroid signaling originated before the emergence ofangiosperms.2. Auxin and jasmonate acid signaling pathways have a common ancestral signalingpathway, and diverged before the emergence of land plants. Cytokinin and ethylene signalingpathways originated from two-component, respectively.3. Only a minor proportion of plant signaling components contain domains which arespecific for land plant, while most of them contain domains which origined from prokaryoticor of algae, suggesting that evolutionary tinkering plays a central role in the origin andevolution of plant signaling. Moreover, land-specific protein domains mainly exist insignaling receptors and inhibitors.4. We just researched rate-limiting enzymes participating every synthesis processesbecause synthesis processes are unexpectedly complicated. Our results showed that most ofthe protein domains contained by enzymes origined from bacteria.