Aluru Maneesha R., Rodermel Steven R.
Department of Genetics, Developmental and Cellular Biology, Iowa State University, Ames, Iowa 50011, USA.
Physiol Plant. 2004 Jan;120(1):4-11. doi: 10.1111/j.0031-9317.2004.0217.x.
Variegation mutants offer excellent opportunities to study interactions between the nucleus-cytoplasm, the chloroplast, and the mitochondrion. Variegation in the immutans (im) mutant of Arabidopsis is induced by a nuclear recessive gene and the extent of variegation can be modulated by light and temperature. Whereas the green sectors have morphologically normal chloroplasts, the white sectors are devoid of pigments and accumulate a colourless carotenoid, phytoene. The green sectors are hypothesized to arise from cells that have avoided irreversible photooxidative damage whereas the white sectors originate from cells that are photooxidized. Cloning of the IMMUTANS (IM) gene has revealed that IMMUTANS (IM) is a plastid homologue of the mitochondrial alternative oxidase. This finding suggested a model in which IM functions as a redox component of the phytoene desaturation pathway, which requires phytoene desaturase activity. Consistent with this idea, IM has quinol oxidase activity in vitro. Recent studies have revealed that IM plays a more global role in plastid metabolism. For example, it appears to be the elusive terminal oxidase of chlororespiration and also functions as a light stress protein.
叶色变异突变体为研究细胞核-细胞质、叶绿体和线粒体之间的相互作用提供了绝佳的机会。拟南芥免疫突变体（im）中的叶色变异由一个核隐性基因诱导，叶色变异的程度可受光照和温度调节。绿色部分具有形态正常的叶绿体，而白色部分缺乏色素并积累一种无色类胡萝卜素——八氢番茄红素。据推测，绿色部分源于避免了不可逆光氧化损伤的细胞，而白色部分则起源于发生了光氧化的细胞。免疫基因（IM）的克隆表明，免疫基因（IM）是线粒体交替氧化酶的质体同源物。这一发现提示了一个模型，即IM作为八氢番茄红素去饱和途径的氧化还原成分发挥作用，该途径需要八氢番茄红素去饱和酶活性。与此观点一致，IM在体外具有喹啉氧化酶活性。最近的研究表明，IM在质体代谢中发挥着更广泛的作用。例如，它似乎是难以捉摸的叶绿体呼吸末端氧化酶，还作为一种光胁迫蛋白发挥作用。
