ARC Centre of Excellence for Translational Photosynthesis, Hawkesbury Institute for the Environment, Western Sydney University, Penrith NSW, Australia.
Plant Science, Rothamsted Research, West Common, Harpenden, Hertfordshire, UK.
J Exp Bot. 2020 Jan 23;71(3):1039-1052. doi: 10.1093/jxb/erz495.
Although sugar regulates photosynthesis, the signalling pathways underlying this process remain elusive, especially for C4 crops. To address this knowledge gap and identify potential candidate genes, we treated Setaria viridis (C4 model) plants acclimated to medium light intensity (ML, 500 µmol m-2 s-1) with low (LL, 50 µmol m-2 s-1) or high (HL, 1000 µmol m-2 s-1) light for 4 d and observed the consequences on carbon metabolism and the transcriptome of source leaves. LL impaired photosynthesis and reduced leaf content of signalling sugars (glucose, sucrose, and trehalose-6-phosphate). In contrast, HL strongly induced sugar accumulation without repressing photosynthesis. LL more profoundly impacted the leaf transcriptome, including photosynthetic genes. LL and HL contrastingly altered the expression of hexokinase (HXK) and sucrose-non-fermenting 1 (Snf1)-related protein kinase 1 (SnRK1) sugar sensors and trehalose pathway genes. The expression of key target genes of HXK and SnRK1 were affected by LL and sugar depletion, while surprisingly HL and strong sugar accumulation only slightly repressed the SnRK1 signalling pathway. In conclusion, we demonstrate that LL profoundly impacted photosynthesis and the transcriptome of S. viridis source leaves, while HL altered sugar levels more than LL. We also present the first evidence that sugar signalling pathways in C4 source leaves may respond to light intensity and sugar accumulation differently from C3 source leaves.
尽管糖调节光合作用，但这一过程的信号通路仍然难以捉摸，尤其是对于 C4 作物。为了解决这一知识空白并确定潜在的候选基因，我们用低光（LL，50 µmol m-2 s-1）或高光（HL，1000 µmol m-2 s-1）处理适应中光强度（ML，500 µmol m-2 s-1）的绿色柳枝稷（C4 模式植物）植株 4 天，并观察其对碳代谢和源叶转录组的影响。LL 会损害光合作用并降低信号糖（葡萄糖、蔗糖和海藻糖-6-磷酸）在叶片中的含量。相比之下，HL 强烈诱导糖积累而不抑制光合作用。LL 对叶片转录组的影响更为显著，包括光合作用基因。LL 和 HL 对比性地改变了己糖激酶（HXK）和蔗糖非发酵 1（Snf1）相关蛋白激酶 1（SnRK1）糖传感器以及海藻糖途径基因的表达。HXK 和 SnRK1 的关键靶基因的表达受到 LL 和糖耗竭的影响，而令人惊讶的是 HL 和强糖积累仅轻微抑制 SnRK1 信号通路。总之，我们证明 LL 深刻地影响了绿色柳枝稷源叶的光合作用和转录组，而 HL 比 LL 更能改变糖水平。我们还首次证明 C4 源叶的糖信号通路可能对光强度和糖积累的反应不同于 C3 源叶。
