Department of Plant Science, Plant Genomics and Breeding Institute, Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul, 151-921, Korea.
Plant J. 2013 Apr;74(1):122-33. doi: 10.1111/tpj.12110. Epub 2013 Mar 4.
protochlorophyllide oxidoreductase (POR) catalyzes photoreduction of protochlorophyllide (Pchlide) to chlorophyllide in chlorophyll (Chl) synthesis, and is required for prolamellar body (PLB) formation in etioplasts. Rice faded green leaf (fgl) mutants develop yellow/white leaf variegation and necrotic lesions during leaf elongation in field-grown plants. Map-based cloning revealed that FGL encodes OsPORB, one of two rice POR isoforms. In fgl, etiolated seedlings contained smaller PLBs in etioplasts, and lower levels of total and photoactive Pchlide. Under constant or high light (HL) conditions, newly emerging green leaves rapidly turned yellow and formed lesions. Increased levels of non-photoactive Pchlide, which acts as a photosensitizer, may cause reactive oxygen accumulation and lesion formation. OsPORA expression is repressed by light and OsPORB expression is regulated in a circadian rhythm in short-day conditions. OsPORA was expressed at high levels in developing leaves and decreased dramatically in fully mature leaves, whereas OsPORB expression was relatively constant throughout leaf development, similar to expression patterns of AtPORA and AtPORB in Arabidopsis. However, OsPORB expression is rapidly upregulated by HL treatment, similar to the fluence rate-dependent regulation of AtPORC. This suggests that OsPORB function is equivalent to both AtPORB and AtPORC functions. Our results demonstrate that OsPORB is essential for maintaining light-dependent Chl synthesis throughout leaf development, especially under HL conditions, whereas OsPORA mainly functions in the early stages of leaf development. Developmentally and physiologically distinct roles of monocot OsPORs are discussed by comparing with those of dicot AtPORs.
原叶绿素氧化还原酶（POR）催化原叶绿素（Pchlide）在叶绿素（Chl）合成中的光还原，并且是质体前体（PLB）在黄化质体中形成所必需的。水稻褪色绿叶（fgl）突变体在田间生长的植物中叶伸长过程中出现黄/白叶斑驳和坏死病变。基于图谱的克隆表明，FGL 编码 OsPORB，是两种水稻 POR 同工型之一。在 fgl 中，黄化幼苗的质体前体中含有较小的 PLB，并且总 Pchlide 和光活性 Pchlide 的水平较低。在恒定或高光（HL）条件下，新出现的绿叶迅速变黄并形成病变。非光活性 Pchlide 水平增加，作为光敏剂，可能导致活性氧积累和病变形成。在短日照条件下，OsPORA 的表达受光抑制，OsPORB 的表达受昼夜节律调节。OsPORA 在发育中的叶片中高水平表达，并在完全成熟的叶片中急剧下降，而 OsPORB 的表达在叶片发育过程中相对稳定，类似于拟南芥中 AtPORA 和 AtPORB 的表达模式。然而，OsPORB 的表达被 HL 处理迅速上调，类似于 AtPORC 的通量依赖性调节。这表明 OsPORB 功能等同于 AtPORB 和 AtPORC 功能。我们的结果表明，OsPORB 对于维持光依赖性 Chl 合成在整个叶片发育过程中，特别是在 HL 条件下，是必不可少的，而 OsPORA 主要在叶片发育的早期阶段发挥作用。通过与双子叶拟南芥的 AtPORs 进行比较，讨论了单子叶植物 OsPORs 在发育和生理上的不同作用。
