玉米自交系叶绿素代谢对热胁迫的响应特征

Response Characteristics of Chlorophyll Metabolism to Heat Stress in Maize Inbred Lines

【目的】阐明热胁迫下玉米叶绿素代谢的调控机制,为玉米耐热研究提供科学依据。【方法】以耐热玉米自交系HZ4和热敏感自交系L9K为材料,于喇叭口至开花期进行热胁迫处理,每隔5 d取样1次,共取样6次,测定叶绿素及其前体物质的含量,采用RT-qPCR测定相关基因的相对表达量。【结果】热胁迫导致HZ4和L9K叶片中叶绿素a、叶绿素b、总叶绿素及其合成前体物质原卟啉Ⅸ(protoporphyrinⅨ,ProtoⅨ)、镁原卟啉Ⅸ(Mg-protoporphyrinⅨ,MgPⅨ)和原叶绿素酸酯(protochlorophyllide,Pchlide)的含量显著下降,δ-氨基乙酰丙酸(δ-aminolevulinic acid,ALA)和单卟啉胆色素原(porphobilinogen,PBG)的含量显著升高,且HZ4的变化幅度小于L9K。6个叶绿素合成相关基因(PBGD、UROD、MgPMT、POR、CHLG、CAO)的表达量显著下调,且在HZ4中的表达量显著高于在L9K中的表达量;4个叶绿素降解相关基因(CBR、CLH、PPH、PAO)的表达量显著上调,且在HZ4中的表达量显著低于在L9K中的表达量。【结论】热胁迫通过下调叶绿素合成基因和上调叶绿素降解基因的表达,导致叶绿素含量下降。阻碍位点在PBG向ProtoⅨ转化阶段,其主要原因是PBGD和UROD基因下调表达。基因差异表达是耐热型和热敏感型玉米叶绿素含量存在差异的分子机制。

[Purpose]To elucidate the regulation mechanism of maize chlorophyll metabolism under heat stress,providing a scientific basis for heat resistance research in maize.[Methods]The heat-tolerant maize inbred line HZ4 and the heat-sensitive maize inbred line L9K were treated under heat stress from the trumpet stage to the flowering stage,with sampling every five days for a total of six times.The contents of chlorophyll and its synthetic precursors were measured,and the relative expression levels of genes related to chlorophyll metabolism were detected by RT-qPCR.[Results]The contents of chlorophyll a,chlorophyll b,total chlorophyll,and synthesis precursors protoporphyrinⅨ(ProtoⅨ),Mg-protoporphyrinⅨ(MgPⅨ),and protochlorophyllide(Pchlide)in maize leaves decreased significantly under heat stress,whileδ-aminolevulinic acid(ALA)and porphobilinoge(PBG)contents increased significantly,with the variation amplitudes of these components being smaller in HZ4 than in L9K.The expression levels of six chlorophyll synthesis-related genes(PBGD,UROD,MgPMT,POR,CHLG,CAO)were significantly down-regulated,with HZ4 showing significantly higher levels than L9K.Meanwhile,four chlorophyll degradation-related genes(CBR,CLH,PPH,PAO)were significantly up-regulated,with expression levels in HZ4 significantly lower than in L9K.[Conclusion]Heat stress results in the decrease of chlorophyll content in maize due to the down-regulated expression of synthesis-related genes and up-regulated expression of degradation-related genes.The sites of inhibition in maize chlorophyll biosynthesis under heat stress are located at the PBG to ProtoⅨtransition stage,mainly due to down-regulation of PBGD and UROD gene expression.The differential expression of chlorophyll metabolism-related genes is the molecular mechanism behind the differences in chlorophyll content between heat-tolerant and heat-sensitive maize.