Origin And Evolution Of The Plant LHOG Gene And Preliminary Functional Detection Of The Rice OsLHOG Gene

The origin of land plants is a critical event in the establishment of modern terrestrial ecosystems.The ancestor of land plants is believed to be evolved from streptophyte algae and some new genes have evolved to facilitate the adaption on land in streptophyte algae.The plant LHOG gene encodes an unknown functional protein with a functionally unknown domanin DUF4091.The homo logs of this gene are present widely in land plants.However,the origin and evolutionary pattern of the plant LHOG gene was not detected.Further more,the biological function of this gene in plants remains unclear at present.In order to illustrate the origin and evolutionary pattern of the plant LHOG gene and to preliminarily reveal its roles in plant growth and development,a combination of bioinformatics and molecular biology were performed in this thesis..In addition,overexpression transgenic lines and CRISPR/Cas9 mutants of OsLHOG were used for further functional analyses.The main results were shown as follows:(1)The typical feature of the plant LHOG gene is that an evolutionary conserved DUF4091 domain in C-terminus of its protein product.This gene does not possess homologous genes in Chlorophyta,but has homologous genes in the Klebsormidi nitens genome of Charophyta.Based on the sequence analysis of this genes in representative plant species,it was found that most plant genomes have only one LHOG gene,and the LHOG protein sequences have high similarity.(2)Blast results reveled that the homo logs of Streptophyta LHOG genes are only present in prokaryotes,including bacteria and Archea.In the phylogenetic trees,all the selected streptophyta LHOG genes formed a single branch with high bootstrap supports,which fell into the branches of CFB group bacteria.In addition,streptophyta LHOG genes show the highest similarity with those in CFB group bacteria.These results suggested streptophyta acquired LHOG gene from CFB group bacteria through a horizontal gene transfer(HGT)event.(3)Adaptive evolution analysis indicated that the Streptophyta LHOG genes have undergone positive selection after a short period of origination from HGT event,while the dominant force contributing to the evolution in Streptophyta was the purifying selection,suggesting that LHOG genes have experienced functional adaptive evolution after the HGT event.(4)The analysis of expression patterns of the rice OsLHOG gene revealed that the transcription of this gene was regulated by multiple abiotic stress including drought,heat,cold and salt and ABA,suggesting that the OsLHOG gene might be involved in plant response to stresses.(5)In order to illustrate the putative biological function of the rice OsLHOG gene,overexpression transgenic lines and CRISPR/Cas9 mutants of OsLHOG were constructed.Compared with the wild-type,rice tillers and 1000-grain weight were increased in overexpression lines.In contrast,both of them decreased in CRISPR/Cas9 mutants,suggesting that this gene might participate in the positive regulation of rice tillers and 1000-grain weight.Our analyses revealed that Streptophyta LHOG genes were acquired from bacteria through an horizontal gene transfer event,and then inherited into land plants.The expression patterns of the rice OsLHOG gene revealed that it was regulated by multiple abiotic stresses.According to the analyses of overexpression transgenic lines and CRISPR/Cas9 mutants of the OsLHOG gene,we preliminarily proved the important roles of this gene in growth of rice.Our results will not only provide the theoretical basis on revealing the origin and molecular evolution of land plants,but also provide important references for further functional detection of the plant LHOG gene.