The Study On Photoperiod Response Genes In Wheat (Triticum Aestivum L.)

Photoperiod response of plant is an important physiological phenomenon which control flowering time by receiveing day length.Wheat(Triticum aestivum L.) is a typical long-day plant and the photoperiod response greatly affects wheat growth period,adaptability and yield.The molecular mechanism of photoperiod pathway has made a great progress in the model species including Arabidopsis and rice in recent years,but it is less clear in wheat,the main food crop in the world.The present study focused on the diversity of Ppd-D1,Ppd-B1,the main photoperiod genes,and the circadian clock gene TaPRRl belonged to the same gene family with Ppds.The progresses were showed as follows:1.Three new diagnostic molecular markers combined with previously reported markers identified five polymorphisms in the Ppd-Dl gene in 495 wheat varieties originating from diverse geographic locations,25 synthetic varieties,and 30 Aegilops tauschii accessions.The discovery,distribution, expression and function of Ppd-D1 haplotypes were investigated.The major results showed as follows. (1) There are six haplotypes of Ppd-D1,named for haplotypeâ… toâ…¥.(2) Haplotypeâ…¡,â…¤andâ…¥were ancient types because they were found in synthetic wheat and Ae.tauschii.Among them,haplotypeâ…¤andâ…¥were lost whereasâ…¡was remained in common wheat during the wheat domestication.(3) Haplotypesâ… -â…¤had a similar expression pattern and all the expression peaks were at the same time,but their levels were different from one to another.The values of expression peaks of haplotypeâ… andâ…¢were the highest and the lowest,respectively.The others were intermediate.(4) Their expression abundance in the morning under the short day photoperiod condition were negatively correlated with the heading time and the haplotypes were associated with main agronomic traits such as thousand grain weight and plant height.(5) Haplotypeâ… varieties distributed mainly in lower latitudes regions, especially Asia,Oceania and Mexico;haplotypeâ…¡varieties were most frequently found in Asia; haploytpeâ…¢were most commonly found in wheat at higher latitudes of Europe and North America. Haplotypeâ…£was widely found in the wheat grown in much larger areas of different continents.2.The transcripts of Ppd-B1 were analyzed in present study,and the main results were as follows:(1) Ppd-B1 is an alternative splicing gene.There were three alternative splicing loci in the forms of exon inclusion,alternative 5' splice site and intron retention,which locate in 5'UTR,exon 5 and intron 6, respectively.The formers two did not change the conserved domains of PRR protein,while the last resulted in a frameshift mutation.(2) Ppd-B1 produces eight different transcripts through alternative splicing.Four of them including complete open reading frame could translate to be functional proteins. The others encoded truncated proteins for translation stopped ahead and they expressed at very low levels.(3) The alternative spliced transcripts of Ppd-B1 were differentially expressed,which were affected by photoperiod response of varieties and photoperiod conditions.The diversity of Ppd-B1 nucleotide acid sequences were detected in present studies.(1) There were six sequences types found in Ppd-B1 promoter region and four types in the gene coding region that were comprised 10 SNP ploymorphisms located on 5'UTR,exons and introns.(2) Each variety has a same promoter sequence and there were also another one sequences in some varieties.(3) There were at least two copies of Ppd-B1 sequences found in some varieties.The preliminary results implied that the diversity of Ppd-B1 sequences probably associated with the gene function for photoperiod response.3.The study on the circadian clock gene TaPRR1(the homolog to TOC1 from Arabidopsis) was carried out.The results were showed.(1) The orthologous gene TaPRR1-A1,TaPRR1-B1,TaPRR1-D1 from A,B and D genomes of hexaploid wheat(Triticum aestivum L.),respectively,were isolated by using homologous cloning combined with cDNA library screening methods.(2) TaPRR1 expressed quickly in the leaves of wheat seedling after germination in short day photoperiod condition,and their expression values increased quickly in the 6th day.(3) The expression of TaPRR1 varied with the cycles of circadian rhythms,but the expression patterns between long day and short day photoperiod conditions were different.TaPRR1 showed a single expression peak in short day period,which was similar to the.expression of TOC1 and OsPRR1 in Arabidopsis and rice,respectively.Under a long day period,TaPRR1 showed two peaks expression pattern.(4) The expressions of TaPRR1-A1,TaPRR1-B1 and TaPRR1-D1 showed some differences under both long day and short day photoperiod.Among them, TaPRR1-D1 expressed with the well circadian rhythm,the poor rhythm for TaPRR1-A1 and intermediate for TaPRR1-B1.(5) The TaPRR1 were located on wheat homoeologous chromosome 6 and TaPRR1-D1 was mapped between RFLP marker Xbcd1716 and Xcfd76 of wheat chromosome 6D with the genetic distances of 4.2 cM and 6.3 cM,respectively.