Mechanisms Of Mechanical Pressure Regulating Cotton Hook Formation

The experiment was conducted with the cotton(Gossypium hirsutum L)variety K638.Under the condition of sand culture,we simulated different mechanical pressures with coverage depth of 1,2,3,and 4 cm of river sand to study the effect of mechanical pressure on apical hook formation of cotton.After 3 days of sowing,the hypocotyl length,diameter and hook angle of cotton seedlings,the contents of hormones such as ethylene,gibberellin and auxin as well as the expression of genes associated with hook formation were measured.Based on those measurements,the apical hooks of 1cm and 3cm covering cotton seedlings were selected and divided into the inner side and the outer side along the longitudinal centerline of the hooks to analyze the expression spectrum,and the differentially expressed genes in the process of forming the hooks were analyzed.The expression pattern of related genes formed by hooks,and the function of related genes was studied by using VIGS gene silencing technology.At the same time,the effect of exogenous ethylene on the formation of cotton hooks and its mechanism were studied.In addition,the effect of seeding rate on the formation of cotton hooks was also investigated.The main results are as follows:1.Mechanical pressure promoted the formation of apical hooks.In this experiment,the angle of apical hook expansion reduced with the greater mechanical pressure which was increased by cover depth.Compared with the 1cm treatment,the angle of cotton apical hook decreased by 28.2%、65.7% and 81.8% respectively with the cover depth of 2cm,3cm and 4cm.At the same time,as the mechanical pressure(cover depth)increase,the expression level of the key gene Gh HLS1 increases.2.Mechanical pressure promoted the formation of apical hook hooks by ethylene.In this experiment,as the mechanical pressure(cover depth)increased,the ethylene in the cotton seedlings also increased.Compared with the depth of 1cm,the ethylene in the cotton seedlings increased by 15.8%,31% and 39.2% respectively with a depth of 2cm,3cm and 4cm.At the same time,with the increase of the depth of coverage,the key genes Gh ACS8 and Gh ACO of cotton ethylene synthesis also increased.In addition,in this test by external application of ethylene,it was found that compared with the control group,the expansion angle of the apical hook was decreased,the ethylene content inside and outside of the apical hook was increased,and the expression of Gh HLS1 on the inside of the apical hook was up-regulated.3.The number of sowing per hole has an effect on the formation of the apical hook by ethylene.In this experiment,compared with cluster seeding,the angle of the apical hook of the monoseeding cotton decreased by 20.7%,and the content of ethylene of the monoseeding cotton increased by 18.2%.The expression of Gh HLS1 and Gh ACS8 of the ethylene synthesis were up-regulated.4.The difference in the distribution of hormones in the inner and outer sides of the apical hook and the differential expression of related genes are the main reasons for the formation of hooks.In this experiment,the apical hooks of 1cm and 3cm covering cotton seedlings were selected and divided into the inner side and the outer side along the longitudinal centerline of the hooks to analyze the expression spectrum,and the differentially expressed genes in the process of forming the hooks were analyzed.The difference in the inner and outer sides of the apical hook is related to the distribution of hormones and the differential expression of a series of related genes.The expression profiling data indicated that the expression of most of the jasmonic acid and gibberellin signal transduction pathway-related genes was higher than that of the inside during the formation of apical hooks,while the expression of the genes related to ethylene and auxin signal transduction pathways was higher than that of outside.In particular,it was identified that the Gh ACS expression levels of genes involved in ethylene synthesis were lower than the inside.In addition,the expressions of Gh GA20ox1,Gh GID1 B and Gh JAZ6 were up-regulated in the outside of cottton grown under 3 cm cover depth compared with the 1cm,which further indicating that the hormone plays a very important role in the formation of the apical hook.In conclusion,mechanical pressure can induce cotton seedlings to produce ethylene,which promotes the expression of Gh HLS1 and thereby promotes the formation of hook.Differential distribution of plant hormone between the inside and outside of hook is the key cause of cell division and growth during the formation of hook.