Department of Ecology and Evolutionary Biology, The University of Toronto, 25 Willcocks Street, Toronto, On M5S3B2 Canada.
Department of Ecology and Evolutionary Biology, The University of Toronto, 25 Willcocks Street, Toronto, On M5S3B2 Canada
J Exp Bot. 2014 Jul;65(13):3341-56. doi: 10.1093/jxb/eru180. Epub 2014 May 6.
In this review, we examine how the specialized "Kranz" anatomy of C4 photosynthesis evolved from C3 ancestors. Kranz anatomy refers to the wreath-like structural traits that compartmentalize the biochemistry of C4 photosynthesis and enables the concentration of CO2 around Rubisco. A simplified version of Kranz anatomy is also present in the species that utilize C2 photosynthesis, where a photorespiratory glycine shuttle concentrates CO2 into an inner bundle-sheath-like compartment surrounding the vascular tissue. C2 Kranz is considered to be an intermediate stage in the evolutionary development of C4 Kranz, based on the intermediate branching position of C2 species in 14 evolutionary lineages of C4 photosynthesis. In the best-supported model of C4 evolution, Kranz anatomy in C2 species evolved from C3 ancestors with enlarged bundle sheath cells and high vein density. Four independent lineages have been identified where C3 sister species of C2 plants exhibit an increase in organelle numbers in the bundle sheath and enlarged bundle sheath cells. Notably, in all of these species, there is a pronounced shift of mitochondria to the inner bundle sheath wall, forming an incipient version of the C2 type of Kranz anatomy. This incipient version of C2 Kranz anatomy is termed proto-Kranz, and is proposed to scavenge photorespiratory CO2. By doing so, it may provide fitness benefits in hot environments, and thus represent a critical first stage of the evolution of both the C2 and C4 forms of Kranz anatomy.
在这篇综述中，我们探讨了 C4 光合作用的特殊“花环”解剖结构是如何从 C3 祖先进化而来的。花环解剖结构是指将 C4 光合作用的生物化学物质分隔开来的环状结构特征，使 CO2 能够在 Rubisco 周围浓缩。利用 C2 光合作用的物种也具有简化版的花环解剖结构，其中光呼吸甘氨酸穿梭途径将 CO2 浓缩到围绕维管束组织的内束鞘状隔室中。C2 花环被认为是 C4 花环进化发展的中间阶段，这是基于 C2 物种在 14 条 C4 光合作用进化谱系中的中间分支位置。在最受支持的 C4 进化模型中，C2 物种的花环解剖结构是从 C3 祖先进化而来的，其束鞘细胞增大，叶脉密度增加。已经确定了四个独立的谱系，其中 C2 植物的 C3 姐妹种表现出束鞘中的细胞器数量增加和束鞘细胞增大。值得注意的是，在所有这些物种中，线粒体明显向束鞘内壁转移，形成 C2 型花环解剖结构的初始版本。这种 C2 花环解剖结构的初始版本被称为原花环，被认为可以清除光呼吸 CO2。这样做可能会在炎热的环境中提供适应性优势，因此代表了 C2 和 C4 形式的花环解剖结构进化的关键第一步。
