Genetic Mechanisms Study Of Drought Tolerance Related To Plant Architecture In Maize (Zea Mays L.)

Maize?Zea mays L.?is one of the most important crops that is utilized as food,animalfeed,and raw material of bioenergy,and its safety production is important for sustainable development of agriculture.Drought is considered one of the most important abiotic stresses that influence agriculture production.Maize is sensitive to drought,and drought stress can adversely affect maize growth,physiological metabolism,and grain yield,even causing 9.3%³5.1%reduction in maize yield.The drought tolerance in maize is a complex quantitative trait,and some drought related traits are controlled by multiple micro-genes.Hence,it is of great significance to reveal the molecular mechanisms of drought related traits and detect functional genes/QTLs,which will give great help in breeding drought-tolerant maize varieties to improve maize production in dry area.Plant architecture in maize are closely consisted with dense planting,lodging,and drought tolerance,moreover the ideal plant type breeding is an important breeding strategy to improve dense planting,lodging,drought tolerance,and yield potential in maize.Therefore,two F₂ populations?POP1-1 and POP2-1?/two F_2:3 populations were derived from Langhuang×TS141 and Chang7-2×TS141 to analyze the relationship between plant architecture/yield component traits and drought tolerance,to identify corresponding QTLs,QTL by environment interaction?QTL×E?,and epistasis interaction,to detect QTLs/stable QTLs?sQTLs?for drought related plant architecture/yield component traits under nine different watering conditions;The consensus map of QTLs for plant architecture/yield component traits were developed via bioinformatics to identify corresponding meta-QTLs?mQTLs?,and the candidate genes were predicted in corresponding mQTLs intervals;One major sQTL for plant architecture trait was used for further fine mapping with one BC₃F₂ population,and the target gene for corresponding trait was detected in the sQTL via individual sequencing technology between parents.The main results are as follows:1.The correlation and clustering analysis by two F2 and two F2:3 populations showed that plant architecture traits and yield component traits were significant correlation with each other.This finding suggested that plant architecture plasticity in maize is the result of the synergistic effect of multiple plant architecture traits,and these traits can significant influence corresponding yield component trait to increase grain yield.2.The performances of plant architecture/yield component traits were analyzed in four maize generations,namely three parents,two F₁ hybrids,and two F_2:3 populations under both four water-stressed and four well-watered conditions.It showed that plant height?PH?,ear height?EH?,plant height-to-ear height ratio?EHPH?,leaf length?LL?,leaf width?LW?,leaf angle?LA?,leaf size?LS?,and tassel branch number?TBN?were significantly reduced,however,leaf orientation value?LOV?and anthesis-silking interval?ASI?were significantly increased in these materials under water-stressed conditions.Moreover,the changes of these corresponding traits in compact/drought-tolerant inbred lines Langhuang and Chang7-2 were more less than flat/drought-sensitive inbred line TS141.These findings showed that stimulates changes in maize plant architecture to decrease light absorption,transpirational loss,and blade temperature under water deficit,even to improve drought tolerance in maize.Additionally,it showed that ear number per plant?EN?,ear weight?EW?,cob weight?CW?,grain weight?GW?,100-kernel weight?KW?,kernel ratio?KR?,and ear length?EL?were significantly reduced in the four generations under drought stress.This finding indicated that these yield component traits also can be used as selection criteria with drought tolerance in maize.3.872 simple sequence repeats?SSRs?were selected from Maize Genome Database?MaizeGDB?,which were located in all ten chromosomes.Then,213 polymorphic SSRs were screened out between Langhuang and TS141 to develop a genetic map,which spanned length of 1542.5cM with an average interval of 7.8cM between markers.Similarly,217 polymorphic SSRs were screened out between Chang7-2 and TS141 to build a genetic map,which was 1648.8cM with an average distance of 8.0cM between markers.4.Using single environment mapping with CIM,136/197 QTLs for PH,EH,EHPH,LL,LW,LA,LOV,LS,ASI,TBN,EN,EW,CW,GW,KW,KR,and EL were mapped in two F₂ populations/two F_2:3 populations,which explained 4.10%¹5.73%or3.37%²6.95%of phenotypic variance in a single environment.For these QTLs,130QTLs were mapped under water-stressed conditions.Further analysis showed that 25sQTLs were detected in two F₂ populations,and 53 s QTLs were mapped under water-stressed conditions in two F_2:3 populations.5.Using joint analysis of all environment with MCIM,148 joint QTLs for these 17plant architecture/yield component traits were identified across two F2:3 populations.Moreover,60/148 QTLs were involved in QTL-by-environment interaction?QTL×E?.In addition,43 pairs of significant epistatic interactions for these 17 traits were identified with additive by additive?AA?,additive by dominance?AD?,and dominance by dominance?DD?epistatic interaction effects among all environments in two F_2:3populations.These findings revealed that except for QTL×E and epistasis,the QTLs for these traits were mainly controlled by main gene effect.6.Using bioinformatics,the first consensus map?7244.9 cM?was developed from661 selected QTLs for LA,LOV,LL,LW,LS,and leaf shape value?LSV?,then 22mQTLs were identified in the map by meta-analysis,and 24 candidate genes were predicted in these mQTLs intervals to regulate the development of plant architecture traits in maize.Similarly,the second consensus map?7246.9cM?was built from 228selected QTLs for TBN and EN,then 20 mQTLs were validated in the map by meta-analysis,and 34 candidate genes were identified in these mQTLs to regulate the development of inflorescence and improvement of stress resistance in maize.And the third consensus map?7244.9cM?was constructed from 794 selected QTLs for PH,EH,EHPH,ASI,EW,CW,GW,KW,KR,EL,and grain yield?GY?,then 36 mQTLs were detected in the map by meta-analysis,and 40 candidate genes were identified in these mQTLs to regulate the development of plant,formation of yield,and improvement of stress resistance?drought tolerance?in maize.7.The BC₃F₂ population?contained 258 individuals?were constructed and 45 new SSRs were developed in this study to fine mapping one major sQTL?umc2177-umc1378?for LA and LOV,the result showed that the sQTL were successfully mapped in marker LA16 to LA19 interval,and the fine mapping further shortened the distance of the sQTL.The number of different SNPs,Indels between parents were 4968525 and1678012,745274 and 250309 via individual sequencing technology,then 258 genes were detected in the sQTL and to identify one target gene?Zm00001d018659_T006?for LA and LOV in the sQTL by GO,COG,KEGG,SwissProt,and Nr annotation.These results can provide valuable information for revealing the drought genetic mechanisms responsible for plant architecture,can lay foundations for the corresponding gene/QTL cloning,and can provide useful targets for marker-assisted selection?MAS?breeding for drought related plant architecture.