Morita Koichi, Hatanaka Tomoko, Misoo Shuji, Fukayama Hiroshi
Laboratory of Crop Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan.
Plant Physiol. 2014 Jan;164(1):69-79. doi: 10.1104/pp.113.228015. Epub 2013 Nov 19.
Rubisco small subunits (RbcSs) are encoded by a nuclear multigene family in plants. Five RbcS genes, OsRbcS1, OsRbcS2, OsRbcS3, OsRbcS4, and OsRbcS5, have been identified in rice (Oryza sativa). Among them, the amino acid sequence of OsRbcS1 differs notably from those of other rice RbcSs. Phylogenetic analysis showed that OsRbcS1 is genetically distant from other rice RbcS genes and more closely related to RbcS from a fern and two woody plants. Reverse transcription-PCR and promoter β-glucuronidase analyses revealed that OsRbcS1 was not expressed in leaf blade, a major photosynthetic organ in rice, but was expressed in leaf sheath, culm, anther, and root central cylinder. In leaf blade of transgenic rice overexpressing OsRbcS1 and leaf sheath of nontransgenic rice, OsRbcS1 was incorporated into the Rubisco holoenzyme. Incorporation of OsRbcS1 into Rubisco increased the catalytic turnover rate and Km for CO2 of the enzyme and slightly decreased the specificity for CO2, indicating that the catalytic properties were shifted to those of a high-activity type Rubisco. The CO2 assimilation rate at low CO2 partial pressure was decreased in overexpression lines but was not changed under ambient and high CO2 partial pressure compared with nontransgenic rice. Although the Rubisco content was increased, Rubisco activation state was decreased in overexpression lines. These results indicate that the catalytic properties of Rubisco can be altered by ectopic expression of OsRbcS1, with substantial effects on photosynthetic performance in rice. We believe this is the first demonstration of organ-specific expression of individual members of the RbcS gene family resulting in marked effects on Rubisco catalytic activity.
核酮糖-1,5-二磷酸羧化酶/加氧酶小亚基（RbcSs）由植物中的一个核多基因家族编码。在水稻（Oryza sativa）中已鉴定出五个RbcS基因，即OsRbcS1、OsRbcS2、OsRbcS3、OsRbcS4和OsRbcS5。其中，OsRbcS1的氨基酸序列与其他水稻RbcSs的序列有显著差异。系统发育分析表明，OsRbcS1在遗传上与其他水稻RbcS基因距离较远，而与一种蕨类植物和两种木本植物的RbcS关系更为密切。逆转录PCR和启动子β-葡萄糖醛酸酶分析表明，OsRbcS1在水稻的主要光合器官叶片中不表达，但在叶鞘、茎、花药和根中柱中表达。在过表达OsRbcS1的转基因水稻叶片和非转基因水稻叶鞘中，OsRbcS1被整合到核酮糖-1,5-二磷酸羧化酶全酶中。将OsRbcS1整合到核酮糖-1,5-二磷酸羧化酶中提高了该酶的催化周转率和对CO2的Km值，并略微降低了对CO2的特异性，表明催化特性向高活性型核酮糖-1,5-二磷酸羧化酶转变。与非转基因水稻相比，过表达株系在低CO2分压下的CO2同化率降低，但在环境和高CO2分压下没有变化。虽然核酮糖-1,5-二磷酸羧化酶含量增加，但过表达株系中核酮糖-1,5-二磷酸羧化酶的活化状态降低。这些结果表明，通过异位表达OsRbcS1可以改变核酮糖-1,5-二磷酸羧化酶的催化特性，对水稻的光合性能产生显著影响。我们认为，这是首次证明RbcS基因家族单个成员的器官特异性表达对核酮糖-1,5-二磷酸羧化酶催化活性产生显著影响。
