Morphological Identification And Genetic Mechanism Research Of A Flower-Defective Mutant In Cosmos

Flower development is important for plants development,which is related to the survival and reproduction of plants,and plants in the process of evolution formed a complex flower structure and inflorescence structure,this is the long-term adaptation of plants to the environment at the same time this affects the normal process of plant reproduction and the way how people use them.Asteraceae is one of the largest families and a relatively young family.Asteraceae plants are represented by their unique capitate-like inflorescences,highly compact inflorescences in the position of a single flower on the branches,so their capitate-like inflorescences can sometimes be called false flowers.Because of the complexity of inflorescence structure and molecular regulation mechanism,the mechanism of flower development regulation in Asteraceae is far less than that of other dicotyledons.Cosmos is an important ornamental plant in Asteraceae.We found a rare mutant cosmos named gh(green head).We have found some mechanism of gene mutation that led to its mutation from studying the morphological characteristics of its flower development and comparing the mutant characteristics with those of wild-type cosmos;the differentially expressed genes of gh mutants at different floral development stages were compared with those of wild-type cosmos by RNA-seq;the key genes related to the flower development of cosmos were cloned,the sequences and expression of the genes in mutant plants were analyzed and compared with those in wild-type plants,and their functions were verified by heterologous transformation.Some speculations were made on the molecular regulation mechanism that may lead to gh mutant traits.The results are as follows:1.We established a rapid propagation and long-term preservation scheme for gh mutants by improving the relevant asexual culture conditions.2.The flower developmental process of the head-like inflorescence of wild-type and mutant cosmos was observed by macroscopic phenotypic observation,anatomical microscopic observation,histological section and scanning electron microscopy.It was found that the relative characters of gh mutant during vegetative growth period were not different from those of wild-type cosmos,and the mutant characters occurred at the early inflorescence development stage.In the early stage of inflorescence development of gh cosmos,the transformation from inflorescence primordium to flower primordium was inhibited,and the flower primordium could not be formed.Instead,the inflorescence primordium which could produce secondary inflorescence repeatedly,and many ectopic bract-like structures were produced.3.We analyzed the transcriptome data of gh plants and wild-type plants in the early stage of flower development.We found that the differentially expressed genes were mainly concentrated in three biological pathways: enzymes with EC numbers,plant-pathogen interaction and protein processing in endoplasmic reticulum.A series of plant physiological changes during flower development in cosmos may have some effects on plant stress response to pathogens and resistance to pathogens.At the same time,we analyzed the differential expression of flower development-related genes between gh mutant and wild-type cosmos in the early and late stages of flower development,and found that the decrease of LFY,UFO,AP1-like and other homologous genes at the early stage of flower development may be an important reason for the decrease of gene expression related to flower organ development.4.We cloned Cb LFY,Cb UFO,Cb AP1-like 1,Cb AP1-like 2,which are the key genes related to the development of cosmos.The sequence analysis,phylogenetic analysis and sequence comparison with other species related homologous genes were carried out.We confirmed that Cb LFY was the homologous gene of LFY,Cb UFO was the homologous gene of UFO,Cb AP1-like1 and Cb AP1-like2 were the homologous genes of FUL gene.We compared the expression of Cb LFY,Cb UFO and Cb AP1-like1 in wild type and gh mutants during flower development by q PCR and in situ hybridization.Cb LFY was microexpressed in vegetative buds and had the highest expression level in the development stage of inflorescence primordium in wild-type cosmos,and then decreased gradually.Cb UFO was microexpressed in leaves and vegetative buds,and had the highest expression during the transformation of inflorescence primordium to flower primordium.These results indicate that it is possible that Cb UFO gene plays a dominant role in the process of inflorescence primordium transformation to flower primordium,and the FUL homologous gene Cb AP1-like1 is expressed in vegetative organs and flower organs,and has the highest expression level in flower buds.The expression of Cb UFO gene in the gh mutant was And,we indicated that the inhibition of Cb UFO gene expression in the gh mutant of cosmos may be the direct cause of its flower-defectivet mutation.5.We constructed 35S: Cb LFY and 35S: Cb UFO vectors and transferred them into Arabidopsis for functional verification.The results showed that transgenic Arabidopsis plants overexpressed with Cb LFY had early flowering and floral organ variation,while transgenic Arabidopsis plants overexpressed with Cb UFO gene had leaf variation and petal increase,but did not show early flowering.These results suggest that Cb LFY and Cb UFO genes are conserved in some parts of Arabidopsis.Cb LFY can regulate the transformation of inflorescence primordia to floral primordia in Arabidopsis,and Cb UFO can only regulate vegetative organs and floral organs development in Arabidopsis.