Japan International Research Center for Agricultural Sciences (JIRCAS), Crop Production and Environment Division, Abiotic Stress Tolerance Group, Ohwashi, Tsukuba, Ibaraki 305-8686, Japan.
J Exp Bot. 2010 Mar;61(5):1405-17. doi: 10.1093/jxb/erq007. Epub 2010 Feb 17.
High surface ozone concentration is increasingly being recognized as a factor that negatively affects crop yields in Asia. However, little progress has been made in developing ozone-tolerant genotypes of rice-Asia's major staple crop. This study aimed to identify possible tolerance mechanisms by characterizing two quantitative trait loci (QTLs) that were previously shown to influence visible leaf symptoms under ozone exposure (120 nl l(-1), 7 h d(-1), 13 d). Two chromosome segment substitution lines (SL15 and SL41) that carried introgressions of the QTLs OzT3 and OzT9, respectively, were exposed to ozone at 120 nl l(-1) along with their parent Nipponbare. In accordance with the expected QTL effect, SL15 showed stronger visible symptoms of ozone damage than Nipponbare, whereas SL41 had fewer symptoms. Gene expression profiling by microarray hybridization yielded 470 probes that were differentially expressed in SL15 and 314 in SL41. Potential tolerance mechanisms were evaluated by investigating changes in gene expression in three general categories. (i) Processes involved in programmed cell death, in which a number of genes related to ethylene or jasmonic acid metabolism or general disease resistance were identified that were differentially regulated in one of the substitution lines. (ii) Biosynthesis of antioxidants. Testing this hypothesis did not reveal any genes differentially regulated between genotypes, and it was thus rejected. (iii) Turnover of antioxidants and enzymatic detoxification of radical oxygen species (ROS), in which a number of differentially regulated genes were also identified. Genes encoding antioxidant enzymes (catalase and peroxidases) tended to be more strongly expressed in SL15. A potential tolerance gene which encodes a putative ascorbate oxidase was identified within the QTL introgression in SL41. This gene showed consistently lower expression in SL41 under ozone exposure across different points in time within independent experiments. Its expression may be involved in mechanisms leading to enhanced ascorbic acid status in SL41 under ozone exposure, and may be linked to a higher concentration of total apoplastic ascorbic acid in SL41 that was observed in an independent experiment.
高浓度的地表臭氧正日益被视为影响亚洲作物产量的一个负面因素。然而，在培育对臭氧具有耐受性的水稻（亚洲主要的主食作物）品种方面，进展甚微。本研究旨在通过鉴定两个先前表明在臭氧暴露下（120 nl l(-1)、7 h d(-1)、13 d）影响可见叶片症状的数量性状位点（QTLs），来确定可能的耐受机制。两个染色体片段代换系（SL15 和 SL41）分别携带 QTLs OzT3 和 OzT9 的导入片段，与亲本 Nipponbare 一起在 120 nl l(-1)下暴露于臭氧。与预期的 QTL 效应一致，SL15 比 Nipponbare 表现出更强的臭氧损伤可见症状，而 SL41 则症状较少。通过微阵列杂交进行的基因表达谱分析产生了在 SL15 中差异表达的 470 个探针和在 SL41 中差异表达的 314 个探针。通过研究三个一般类别中基因表达的变化来评估潜在的耐受机制。（i）程序性细胞死亡过程，其中鉴定出一些与乙烯或茉莉酸代谢或一般抗病性相关的基因，它们在一个代换系中受到差异调控。（ii）抗氧化剂的生物合成。对这一假说的测试并未揭示基因型之间差异调控的任何基因，因此被否定。（iii）抗氧化剂的转化和活性氧（ROS）的酶促解毒，其中还鉴定出一些差异调控的基因。编码抗氧化酶（过氧化氢酶和过氧化物酶）的基因在 SL15 中表达倾向更强。在 SL41 的 QTL 导入片段中鉴定出一个潜在的耐受基因，该基因编码一种假定的抗坏血酸氧化酶。在不同的时间点和独立实验中，该基因在臭氧暴露下在 SL41 中的表达始终较低。它的表达可能与臭氧暴露下 SL41 中抗坏血酸状态增强的机制有关，并且可能与在独立实验中观察到的 SL41 中总质外体抗坏血酸浓度较高有关。
