The Function Of Different Alleles And Mechanism Underlying Transcription Regulatory Of ZmCCT

Flowering time is a significant factor affecting yield and adaption zones of maize.Stalk rot is one of the most destructive corn diseases worldwide.In China,it caused nearly 5%-10%yield losses every year.Previous studies have showed that ZmCCT tended to have pleiotropism.ZmCCT was found to modulate flowering time by photoperiodic pathway,which was one of the most significant genes for maize flowering time and adapting to temperate zones.Meanwhile,ZmCCT was the causal gene at the qRfg1,which could significantly enhance maize resistance to Gibberella stalk rot.A polymorphic CACTA-like transposable element(TE)2.4 kb upstream of ZmCCT is the genetic determinant of allelic variation for flowering time and resistance to stalk rot.The presence or absence of TE insertions at the ZmCCT promoter region has led to the substantial divergence of Zm CCT promoter sequence.At least 15 ZmCCT haplotypes have been isolated,of which 9 have no TE insertion(non-TE).Nine non-TE ZmCCT haplotypes were introgressed into seven elite maize inbred lines by marker-assisted backcrossing.All backcrossing progeny and converted hybrids tested resistance to maize stalk rot and flowering time.Secondly,the effect of ZmCCT on root length and dry weight under low nitrogen and high salt stress conditions and expression pattern of ZmCCT and marker genes response to stress of stress after stress were studied.Finally,the mechanism of transcription regulation of ZmCCT was studied.Main results are as follows:1.Nine resistant non-TE ZmCCT haplotypes were introgressed into Zheng58,Chang7-2,83B28,A5302,Jing24,F349,Yu87-1 seven elite maize inbred lines.We conducted foreground selection,recombinant selections,phenotypic selection and background selection and achieved 63 converted inbred lines had 0.7-5.1 Mb of resistant ZmCCT donor segments with over 90%recovery rates.2.All converted lines tested exhibited enhanced resistance to maize stalk rot but varied in photoperiod sensitivity.Non-TE ZmCCT-directed photoperiod sensitivity depended on genetic background.3.ZmCCT haplotypes had a dose-dependent effect on flowering time,resistance to stalk.The heterozygote of ZmCCT has a positive effect on yield related traits,such as,ear length and 100-kernel weight,and yield in hybrids.Of nine resistant ZmCCT haplotypes,haplotype H5 exhibited excellent performance for both flowering time and stalk rot resistance and is thus expected to have potential value in future China maize breeding programs.4.Under low nitrogen and high salt stress conditions,non-TE ZmCCT could improve plant root growth by using scanner and related softwares.The expression level of ZmCCT was increased and then decreased after stress by Real-time PCR analysis.ZmCCT could respond to low nitrogen and high salt stress conditions and enhance the adaption to abiotic stress of maize.5.The transactivation activity assay of ZmCCT was studied in the yeast GAL4 system.We discovered ZmCCT had strong transactivation activity.The region before CCT domain was essential for its transactivational activity.6.2×Flag-ZmCCT label vector was constructed and transferred into maize receptor B73.T1 transgenic plants were derived.A ZmCCT prokaryotic expression vector was constructed,in order to study the DNA target sequence of ZmCCT protein and explains pleiotropic molecular mechanism.