Abstract：
The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvate carboxykinase (PEPCK) subtypes of C4 photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea. We explore this inconsistency here via an analytical model that features explicit descriptions across a seamless gradient between C4 biochemistries to analyse light harvesting and dark photosynthetic metabolism. Our simulations show that the NADP-ME subtype, operated by the most productive crops, is the most efficient. The NAD-ME subtype has lower efficiency, but has greater light harvesting plasticity (the capacity to assimilate CO2 in the broadest combination of light intensity and spectral qualities). In both NADP-ME and NAD-ME backgrounds, increasing PEPCK activity corresponds to greater light harvesting plasticity but likely imposed a reduction in photosynthetic efficiency. We draw the first mechanistic links between light harvesting and C4 subtypes, providing the theoretical basis for future investigation.
摘要：
NADP-苹果酸酶（ME）的反复出现，C4光合作用的NAD-ME和磷酸烯醇丙酮酸羧激酶（PEPCK）亚型是趋同进化的标志性例子，这表明这些生物化学物质不会随机组装，而是由未知的进化驱动因素导致的特定适应。基于经典生物化学理解的理论研究已经反复提出光利用效率作为PEPCK亚型的可能益处。然而,量子产率测量不支持这个想法。我们在这里通过一个分析模型来探索这种不一致性，该模型在C4生物化学之间的无缝梯度上具有明确的描述，以分析光收获和暗光合代谢。我们的模拟表明，NADP-ME亚型，由最有生产力的作物经营，是最有效的。NAD-ME亚型的效率较低，但是具有更大的采光可塑性（在光强度和光谱质量的最广泛组合中吸收CO2的能力）。在NADP-ME和NAD-ME背景下，增加PEPCK活性对应于更大的采光可塑性，但可能会降低光合效率。我们得出了光捕获和C4亚型之间的第一个机械联系，为今后的调查提供理论依据。
