Study On Physiological And Molecular Mechanism Of Time Course Of Early Maturity In Weedy Rice(Oryza Sativa L.f.spontanea)

Weedy rice(Oryza sativa L.f.spontanea)and cultivated rice(Oryza sativa L.)are regarded as the same species,and they share common or similar morphological and physiological traits.The damage of weedy rice to cultivated rice has become more and more serious,and weedy rice has been considered as one of the three worst weeds in paddy fields worldwide.One of the key reasons why weedy rice becomes a weed is early maturity,which can cause early shattering or early withering of weedy rice to persist by escaping artificial harvesting in the paddy fields.However,the time course and the formation mechanism of early maturity in weedy rice are not well understood.A selected sample of both weedy and associated cultivated rices from Maoming,Taizhou,Yangzhou,Dandong city was sown under different day-length and sowing date conditions,flowering time,period related to grain filling and morphological characteristics of weedy rice and associated cultivated rice were quantitatively observed.We observed and measured the grain filling rate,ethylene evolution rate,ABA content,the activities of key enzymes and expressions of genes involved in starch synthesis pathway of both weedy and cultivated rice.We compared the methylation level of the promoter and coding region of OsEIL1,OsEIL3,OsERF3 in the ethylene pathway of weedy rice and cultivated rice.We also measured the expression levels of OsEIL1,OsEIL3,OsERF3,OsEBP-89.Comprehensive analysis was made on the correlation of those indexes with the period related to grain filling of the biotypes.The main study results are given as followings:1.Studies on responses of reproductive growth period and agronomic traits to day-length in weedy and cultivated riceThe flowering time of weedy rice were 2-30 d shorter than that of associated cultivated rice under natural long-day condition.The flowering strategies of weedy rice have diverged under short day condition.Compared with the short day conditions,the whole growth period of all populations were significantly larger under the natural long day conditions.The photoperiod sensitivity of weedy rice was significantly lower than that of associated japonica cultivated rice,while the photoperiod sensitivity of weedy rice was significantly higher than that of associated indica cultivated ric,while the basic vegetative growth showed the opposite rhythm.Regardless of day length,grain filling period of weedy rice was shorter than that of cultivated rice.Compared with short day conditions,most of agronomic trait indexes were larger under natural long day conditions.Regardless of day length,the whole growth periods of weedy rice were significantly shorter than that of cultivated rice.2.Early flowering and rapid grain filling determine early maturity and escape from harvesting in weedy riceThe growth periods of weedy rice were 10-38 d shorter than that of associated cultivated rice under conventional sowing dates,while under the delayed sowing dates the growth period was 8-37 d shorter than the later.Under conventional sowing dates,weedy rice accessions flowered 3-26 d earlier than their associated cultivars in both years,with the exception of the local pair from Yangzhou(YZCR and YZWR)which did so simultaneously.Delayed sowing caused divergence in the flowering regimes in weedy rice,and the flowering time of weed rice in Jiangsu is later than that of cultivated rice.However,regardless of the sowing date,the grain filling period of weedy rice was shorter than that of cultivars in both study years.Under the conventional sowing dates,the grain filling period of weedy rice was 10-30 d shorter than that of cultivated rice,and while the grain filling period of weedy rice was 4-36 d shorter than that of cultivated rice under delayed sowing dates.Vegetative and reproductive traits of weedy and cultivated rice had different variation patterns with delayed planting.Under the same sowing daes conditions,the 1000-grain weight and seed setting rate(%)of weedy rice were lower than that of associated cultivated rice,the shattering rate(%)of weedy rice were larger than that of associated cultivated rice.In a word,regardless of sowing dates,the growth period and grain filling period of weedy rice were shorter than that of associated cultivated rice.3.Ethylene and ABA mediated rapid grain filling of weedy rice to promote early maturityAfter fertilization,the grains began to fill,and both of them entered milk stage first.Grain filling tended to stabilize and then entered soft dough stage,and the pericarp color of weedy rice changed from green to brown at 9-10 DPA,while grain filling of cultivated rice tended to stabilize and then entered soft dough stage at 15-18 DPA,and the pericarp color changed from green to white.Weedy rice completed grain filling 6-8 days earlier than cultivated rice.The grain filling rate of weedy rice was significantly higher than that of cultivated rice.The maximum grain-filling rate of weedy rice was 11.6%-39%higher than that of cultivated rice,the grain filling termination time(T)of weedy rice was 5-13d shorter than that of cultivated rice.Very similar to the grain filling rate,the SuSase activity change curve contained a single peak:the activity of SuSase(assayed in cleavage direction),at the early grain filling stage was relatively low,followed by increased activity as grain filling progressed and then a rapid decrease.Changes in the expression levels of SuSase genes,SuS2 and SuS4,were consistent with those in the activity of SuSase in both weedy and cultivated rice:relatively low in the early stage of the grain filling period,reaching a maximum during the middle of the filling stage,and then gradually declining thereafter,and it took shorter for gene expression level to reach its peak in weedy rice than in cultivated rice.Changes in the activities of key enzymes in starch synthesis,AGPase,SSS,GBSS,and SBE were very similar to those in the grain filling rate and activity of SuSase.Activities of these enzymes reached the peak more highly and earlier in weedy rice than in cultivated rice.The genes AGPS1,AGPS2b,AGPL2,GBSSⅠ,SSSⅡa,SSSⅡc,SBEI were all related to key starch synthesis enzymes.The changes in their expression levels were similar to those in AGPase,SSS,and SBE enzyme activity,in good agreement with the grain filling rate.ABA content of weedy rice was much greater in weedy rice than in associated cultivar at the early grain filling stage(3-10 DPA),and ABA content was significantly lower than that of associated cultivated rice at the middle grain filling stage(15-25 DPA).In a sharp contrast to ABA,ethylene evolution rate,ACC content,ACC synthase,ACC oxidase from grains were high at the early grain-flling stage,and decreased thereafter in both weedy rice and associated cultivated rice.ABA,not ethylene,was significantly positively correlated with filling rate,but there was a significant negative correlation between ethylene metabolism and grain filling-related periods.Exogenous supply of ethephon(an ethylene-releasing reagent)not only suppressed the activities of key enzymes and expressions of genes involved in sucrose-to-starch conversion but also shortened the filling period.4.Study on the mechanism of OsEIL1 methylation regulating ethylene level lead to early maturity of weedy riceExpression level of OsEILl in weedy rice were 26%-89%higher than that in cultivated rice.The number of methylation sites in the coding region of the OsEIL1 gene in weedy rice is 4-7 more than that in associated cultivated rice.The expression level of OsERF3 in weedy rice was 1.4-2.1 times higher than that in associated cultivated rice.The expression level of OsEBP-89 in weedy rice was 1.7-3.3 times higher than that in the associated cultivated rice.There was a significant positive correlation between the expression level and the methylation site in the coding region of OsEIL1 gene,while there was no correlation between expression level and methylation sites of OsEIL3 and OsERF3.BRW,periods related to grain filling(Active grain filling period,Grain filling termination time,Milk stage,Soft dough stage and Hard dough stage)were significantly and negatively correlated with the expression levels of OsEIL1,OsERF3,OsEBP-89 and the number of methylation sites of OsEIL1,respectively.Indexes related to ethylene metabolism were significantly and positively correlated with the expression levels of OsEIL1,OsERF3,OsEBP-89 and the number of methylation sites of OsEIL1,respectively.