玉米脱镁叶绿酸氧化酶基因ZmPAO表达与叶绿素含量动态变化的关联分析

Association profiles between the expression of pheophorbide a oxygenase gene ZmPAO and dynamic variation of chlorophyll contents in maize

【目的】分析玉米脱镁叶绿酸氧化酶基因ZmPAO序列多态性,并挖掘该基因与玉米成熟后期穗位叶叶绿素组分含量相关的功能位点,为基于ZmPAO开发功能标记提供结构信息,有助于对玉米成熟后期叶绿素代谢遗传机制的理解。【方法】以141份具有广泛遗传变异的玉米自交系为试验材料组成关联群体,以2个环境7个时间点的叶绿素组分含量为表型数据,利用Tassel 5.0通过混合线性模型(MLM,mixed linear model)开展玉米脱镁叶绿酸氧化酶基因(ZmPAO)与成熟后不同时期叶绿素组分变化的相关变异位点的关联分析,并对性状的有效关联位点进行单倍型分析。【结果】在玉米生长后期大部分取样时间点的叶绿素组分含量变异较大,叶绿素a普遍低于叶绿素b的含量,最终总叶绿素(叶绿素a与叶绿素b的和)有下降趋势。结果共鉴定ZmPAO中19个有效功能位点,其中4个处于外显子区,1个位于UTR区域,其他均位于内含子区域;功能位点对叶绿素组分含量变异的表型解释率在3.89%~16.57%,总表型效应在5.24%~41.78%。来自第6个内含子的位点S3235对于Yang-chlb6有高达16.57%的表型解释率;第7外显子S3675分别解释了Yang-chla1和Yangchlb1表型变异的12.16%和14.14%。性状显著单倍型中有利位点和关联分析的变异位点偏好相似。【结论】有效功能位点挖掘和性状单倍型分析表明,ZmPAO外显子发生了2个氨基酸变异,均由疏水氨基酸转化为亲水氨基酸,说明该基因可能通过蛋白结构的变异进行调控,但较多关联位点处于非编码区,说明该基因也受转录水平的调控。转录水平受环境影响较大,故导致该基因出现不同地点因播期和生育期的不同找到的关联位点并不一致,但有效变异位点的存在具有普遍性。

【Objectives】To better understand the polymorphism of pheophorbide a oxygenase gene (ZmPAO) in maize and the functional sites related to the contents of chlorophyll components in maize ear leaves, the structural information used for the development of ZmPAO functional markers was analyzed to clarify the genetic mechanism of chlorophyll metabolism at late maturity stage of maize.【Methods】A total of 141 of maize inbred lines with extensive genetic variation was used as a related population. The chlorophyll component contents in two sites from 7 time points were measured as phenotypic data. Tassel 5.0 was used to analyze the relationship between the expression profiles of pheophorbide a oxygenase gene (ZmPAO) and the changes of chlorophyll components at different periods after maturity by the mixed linear model (MLM, Mixed linear model), and the effective association sites were investigated by haplotype analysis.【Results】The chlorophyll contents at the late growth stage of maize revealed greater variation, and chlorophyll a generally has lower accumulation than chlorophyll b, but the total chlorophyll (the sum of chlorophyll a and chlorophyll b) showed a downward trend. A total of 19 of effective functional sites were identified, in which 4 sites were existed in the exon region, one of them located at UTR and others settled in the intron. The phenotypic interpretation rate in the functional site for chlorophyll component content variation was ranged from 3.89% to 16.57%, the total phenotypic effect ranged from 5.24% to 41.78%. Site S3235 from the sixth intron had a phenotypic interpretation rate of 16.57% for Yangchlb6;Site S3675 of the seventh exon represented 12.16% phenotypic interpretation rate for the phenotypic variation for Yang-chla1 and 14.14% for Yang-chlb1, respectively. The favorable trait sites with obvious haplotypes was the same as preferred variation sites in association analysis.【Conclusions】The excavation of effective functional sites and haplotype analysis of traits showed that two amino acids mutated in the ZmPAO exon, and the hydrophobic amino acids were transformed into hydrophilic amino acids, indicating that the ZmPAO gene might be regulated by the protein structure variation and as well as the transcriptional level because more related sites appeared in noncoding regions, although they are not yet identified. However, the transcription level is greatly affected by environmental factors which usually lead to the inconsistency of the related sites that found in different locations of the gene at different growth stages, but the existence of effective mutation sites is universal.