State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, South China Agricultural University, Guangzhou, China.
PLoS One. 2012;7(6):e39658. doi: 10.1371/journal.pone.0039658. Epub 2012 Jun 26.
Glycolate oxidase (GLO) is a key enzyme in photorespiratory metabolism. Four putative GLO genes were identified in the rice genome, but how each gene member contributes to GLO activities, particularly to its isozyme profile, is not well understood. In this study, we analyzed how each gene plays a role in isozyme formation and enzymatic activities in both yeast cells and rice tissues. Five GLO isozymes were detected in rice leaves. GLO1 and GLO4 are predominately expressed in rice leaves, while GLO3 and GLO5 are mainly expressed in the root. Enzymatic assays showed that all yeast-expressed GLO members except GLO5 have enzymatic activities. Further analyses suggested that GLO1, GLO3 and GLO4 interacted with each other, but no interactions were observed for GLO5. GLO1/GLO4 co-expressed in yeast exhibited the same isozyme pattern as that from rice leaves. When either GLO1 or GLO4 was silenced, expressions of both genes were simultaneously suppressed and most of the GLO activities were lost, and consistent with this observation, little GLO isozyme protein was detected in the silenced plants. In contrast, no observable effect was detected when GLO3 was suppressed. Comparative analyses between the GLO isoforms expressed in yeast and the isozymes from rice leaves indicated that two of the five isozymes are homo-oligomers composed of either GLO1 or GLO4, and the other three are hetero-oligomers composed of both GLO1 and GLO4. Our current data suggest that GLO isozymes are coordinately controlled by GLO1 and GLO4 in rice, and the existence of GLO isozymes and GLO molecular and compositional complexities implicate potential novel roles for GLO in plants.
乙醇酸氧化酶（GLO）是光呼吸代谢中的关键酶。在水稻基因组中鉴定出了 4 个假定的 GLO 基因，但每个基因成员如何贡献于 GLO 活性，特别是其同工酶谱，尚不清楚。在这项研究中，我们分析了每个基因在酵母细胞和水稻组织中同工酶形成和酶活性中的作用。在水稻叶片中检测到 5 种 GLO 同工酶。GLO1 和 GLO4 主要在水稻叶片中表达，而 GLO3 和 GLO5 主要在根中表达。酶活性测定表明，除 GLO5 外，所有在酵母中表达的 GLO 成员都具有酶活性。进一步的分析表明，GLO1、GLO3 和 GLO4 相互作用，但 GLO5 没有相互作用。在酵母中共同表达的 GLO1/GLO4 表现出与水稻叶片相同的同工酶模式。当沉默 GLO1 或 GLO4 时，两个基因的表达都同时受到抑制，大部分 GLO 活性丧失，与此观察结果一致，在沉默的植物中检测到很少的 GLO 同工酶蛋白。相比之下，当沉默 GLO3 时没有观察到可检测的效果。在酵母中表达的 GLO 同工型与来自水稻叶片的同工型之间的比较分析表明，这 5 种同工型中的两种是由 GLO1 或 GLO4 组成的同型寡聚体，而另外三种是由 GLO1 和 GLO4 组成的异型寡聚体。我们目前的数据表明，在水稻中，GLO 同工型由 GLO1 和 GLO4 协调控制，GLO 同工型的存在和 GLO 分子和组成的复杂性暗示 GLO 在植物中可能具有新的作用。
