The "Florigen–Antiflorgen" Hormone Systems Modified Flowering Transition And Plant Architecture In Cotton

Plant florigen FLOWERING LOCUS T（FT）protein promotes flowering and regulates determinate growth,while antiflorigen CENTRORADIALIS/TERMINAL FLOWER1/SELF-PRUNING（CETS）proteins inhibits flowering transition and promotes indeterminate growth of meristem.In the apical meristem of plants,FT and CETS compete with the b ZIP transcription factor FD protein to form“florigen activation complex（FAC）”and“anti-florigen complex”respectively,which regulate the vegetative growth and reproductive growth of plants,and ultimately determine the flowering time and plant architecture.In some crops,the mutation or expression expression of genes related to the“florigen–antiflorigen”system lead to the change of flowering phase,growth stage and plant architecture,which provides important genetic resources for the breeding of ideal plant architecture,and also make an important contribution to the improvement of crop cultivation mode and mechanized production.As an important economic crop,cotton（Gossypium hirsutum L.）architecture and growth stage are important factors affecting planting density,cultivation mode and mechanical picking.The improvement of cotton“florigen–antiflorigen”system can shape the ideal plant architecture,adjust the growth stage of cotton,and improve yield and mechanical production efficiency.The aim of this study was to reveal the potential molecular mechanism of cotton flowering transition and plant architecture development by studying the functions of GhFT,Gh14-3-3,GhFD and GhCETS,and to provide theoretical basis and gene elements for the improvement of cotton plant architecture.In addition,we further explored the effects of the genes related to the“florigen–antiflorigen”system on plant root structure development and nitrogen use efficiency,to provide a reference basis for the exploration and utilization of new gene functions.The main contexts and results of this study are as followa.1.Function of cotton FAC.Cotton genome contains only one GhFT gene that promotes flowering.A florigen receptor Gh14-3-3,which interacts directly with GhFT,was found through yeast screening library.There are five b ZIP transcription factors GhFD in cotton,which can be divided into two subclasses in evolution.GhFD1/2 have high similarities with Arabidopsis FD homologous genes.GhFD3/4/5 is unique to mallow.GhFT,Gh14-3-3 and five GhFDs proteins can interact in the nucleus to form three complexes.The functions of GhFDs involved in the regulation of cotton flowering time and root development.On the one hand,GhFT–Gh14-3-3–GhFD1/2 complex in shoot apical meristem could activate the expression of floral identity gene APETALA1 homolog in cotton,thus promoting flowering transition.On the other hand,GhFT–Gh14-3-3–GhFD3/4/5 complex in root activated AUXIN RESPONSE FACTOR19 homolog in cotton and promoted the development of cotton lateral roots.Analysis of GhFT–Gh14-3-3–GhFDs complex regulatory module reveals the internal mechanism of cotton flowering transition and the functional diversities of FAC complex at the molecular level.2.Function of antiflorigen gene in cotton.In cotton genome,there are three homologous genes named Gh SP,Gh TFL1-1 and Gh TFL1-2,which are highly expressed in roots,stems and floral organs of cotton,but barely expression in other tissues.Ectopic overexpression of three genes all promoted the vegetative growth of Arabidopsis thaliana and inhibited the flowering transition.Silencing of these three genes in cotton separately could promote cotton flowering.In addition to promoting early flowering,Gh SP silencing also terminate the indeterminated growth of cotton stem,resulting in self-capping and plant height reduction.In tetraploid cotton,the natural variation of gosp allele will lead to fruit branch shortening.In G.barbadense,Gbsp^113Ser mutation type produces zero type fruit branch,and in G.hirsutum,Ghsp^73Asn mutation produces cluster bolls,although the shoot-indeterminate state of the inflorescence is maintained.Gh SP,Gh TFL1-1 and Gh TFL1-2 can interact with GhFD1 and Gh14-3-3 in plant cells,respectively,but the mutant proteins of Ghsp and Gbsp can not interact with GhFD1.3.Regulation of plant root development and increase of nitrogen use efficiency by antiflorigen protein.In Arabidopsis,high nitrogen can up-regulate the transcription of TFL1 gene,and expression of TFL1protein,and increase the protein stability of TFL1 protein.Compared with wild type,tfl1-1 mutants are more sensitive to low nitrogen and produce longer main and lateral roots.Overexpression of TFL1 could simultaneously increase the biomass of the above-ground and underground parts of plant,increase the nitrate uptake rate and nitrate reductase activity of the root system,but severely delay the flowering of the plant.TFL1 gene was specifically expressed in roots,which can maintain the biomass and grain yield of plants under low-fertility conditions without affecting the flowering time of plants.In conclusion,although there is only one florigen in cotton,the different functions of five GhFD proteins in cotton carry out the diversities of functions in cotton florigen activation complex.There are three CETS genes in cotton,which can regulate flowering time,indeterminate growth and development of fruit branchs.These resuls indicate that the molecular module of the“florigen–antiflorigen”system of cotton regulate many aspects of growth and development.Moreover,in A.thaliana,antiflorigen genes can also increase nitrogen use efficiency and plant biomass,which also provides references and new genetic resources for the cultivation of new cotton varieties with less economic input and more output.