Genome-Wide Identification,Comparative Evolution Of Flowering Pathway In Brassicaceae And Expression Characterization Of Genes Related To Flowering In Arabidopsis Pumila

Flowering is an important physiological process in higher plants,marking the transition from vegetative to reproductive growth.Previous studies have shown that flowering-related genes are involved in eight pathways: Photoperiod,Vernalization,Aging,Hormones,Ambient temperature,Sugar,Autonomous and Circadian clock pathway,but some key genes,as key integrators,are involved in many flowering pathways.It is of great significance to thoroughly identify the flowering regulatory genes in different plant and address the adaptation mechanisms between flowering and environment.Ephemeral plants are widely distributed in the arid desert zone of Central Asia and can adapt to extreme habitats to complete their life cycle quickly.However,the molecular mechanisms underlying the rapid flowering transition in ephemeral plants are still poorly understood.Arabidopsis pumila,an early spring ephemeral plant,is mainly distributed in Xinjiang,China,which possesses the characteristics of drought tolerance,low temperature and salinity resistance.Understanding the mechanism of flowering transition in A.pumila provides a theoretical basis for insight into the molecular mechanism of plant adaptation to extreme habitats and flowering transition.In this study,genome-wide identification of flowering pathway members,genetic network analysis and comparative evolution of related gene families were investigated,and the main findings are as follows.(1)We carried out the identification and comparative evolutionary analysis of flowering pathway gene members in the Brassicaceae A.thaliana,A.pumila,and Camelina sativa.A total of 520 genes in A.pumila and 871 genes in C.sativa were identified and divided into eight categories according to their evolutionary relationships,and all of them showed uneven distribution on chromosomes.FLOWERING LOCUS C(FLC),a key gene in the flowering pathway,is absent in A.pumila and only one FLC gene is present in C.sativa.The genes in the Aging and Vernalization pathway underwent greater selection pressure than genes in other pathways,but overall flowering-related genes were purifying selection.(2)Identification,gene structure,protein motif and comparative evolutionary analysis of the members of the Sugar pathway related to flower in the genomes of seven species of Brassicaceae,including A.thaliana,A.lyrate,A.pumila,C.sativa,Brassica rapa,B.oleracea and B.napus.A total of 105 members were identified and classified into nine groups based on evolutionary relationships.The INDETERMINATE DOMAIN 8(IDD8)gene showed striking structural variations in different Brassicaceae species.All members had Ka/Ks less than 0.3.105 members underwent varying degrees of gene expansion during evolution,but SUCROSE SYNTHASE 4(SUS4)and SUCROSE-PROTON SYMPORTER 9(SUC9)were lost in the genomes of A.pumila,C.sativa,B.napus,B.oleracea,and B.rapa,respectively.SUC9 was also lost in A.lyrata.The tissue expression trends of A.pumila genes were divided into two categories,with high expression in early growth stage tissues and highly expressed in mid-to-late-growth tissues.However,the expression trends of paralogous homologs were similar,with only ADP GLUCOSE PYROPHOSPHORYLASE 1(ADG1)showing differential expression.A.pumila flowering-related proteins mainly interacted with proteins related to glycoconjugate synthesis,metabolism,and transport.(3)Genome-wide identification,structural characterization and comparative evolution of TCP(TEOSINTE BRANCHED 1,CYCLOIDEA,PROLIFERATING CELL FACTORS)gene members in the genomes of A.thaliana,A.lyrata,A.pumila and C.sativa were carried out.A total of 163 TCP members were identified,which could be classified into three subfamilies,Class I,CYC and CIN.All TCP proteins contained motif 1,but they also have unique conserved structural domains among different subfamilies.Both orthologous and paralogs of TCP genes were subject to strong purifying selection.Four Brassicaceae TCP genes underwent expansion,but A.pumila was no collinear relationship with At TCP11,and C.sativa was no collinear relationship with At TCP11 and At TCP23.Overexpression of ApTCP35 in A.thaliana and Oryza sativa resulted in distinct early flowering phenotypes.Several endogenous flowering genes in the transgenic plants,including APETALA1(AP1)and FRUITFULL(FUL)in A.thaliana and MADS14/15/18 in O.sativa,were significantly upregulated,indicating that ApTCP35 plays an important role in flowering transition.In summary,this study showed that most members of the flowering pathway genes were expanded in the A.pumila genome,but a few genes such as FLC were missing.It is also found that TCP35 plays an important role in regulating the flowering transition.This study explored the mechanism of flowering maturation in A.pumila adapted to the desert environment in Xinjiang in terms of identification,comparative evolution and genetic network of flowering regulatory pathway-related genes,laying the foundation for the comparative genomics study of ephemeral plant.The flowering-related genes identified in this study provided genetic resources for crop genetic improvement.