Sucrose accumulation and decreased photosynthesis are early symptoms of yellow canopy syndrome (YCS) in sugarcane (Saccharum spp.), and precede the visual yellowing of the leaves. To investigate broad-scale gene expression changes during YCS-onset, transcriptome analyses coupled to metabolome analyses were performed. Across leaf tissues, the greatest number of differentially expressed genes related to the chloroplast, and the metabolic processes relating to nitrogen and carbohydrates. Five genes represented 90% of the TPM (Transcripts Per Million) associated with the downregulation of transcription during YCS-onset, which included PSII D1 (PsbA). This differential expression was consistent with a feedback regulatory effect upon photosynthesis. Broad-scale gene expression analyses did not reveal a cause for leaf sugar accumulation during YCS-onset. Interestingly, the midrib showed the greatest accumulation of sugars, followed by symptomatic lamina. To investigate if phloem loading/reloading may be compromised on a gene expression level – to lead to leaf sucrose accumulation - sucrose transport-related proteins of SWEETs, Sucrose Transporters (SUTs), H⁺-ATPases and H⁺-pyrophosphatases (H⁺-PPases) were characterised from a sugarcane transcriptome and expression analysed. Two clusters of Type I H⁺-PPases, with one upregulated and the other downregulated, were evident. Although less pronounced, a similar pattern of change was observed for the H⁺-ATPases. The disaccharide transporting SWEETs were downregulated after visual symptoms were present, and a monosaccharide transporting SWEET upregulated preceding, as well as after, symptom development. SUT gene expression was the least responsive to YCS development. The results are consistent with a reduction of photoassimilate movement through the phloem leading to sucrose build-up in the leaf.

中文翻译：

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受YCS影响的甘蔗叶中肋糖积累和糖转运蛋白基因表达

蔗糖积累和光合作用降低是黄色篷综合征的早期症状（YCS）在甘蔗（甘蔗属spp。），并在叶片视觉发黄之前。为了调查YCS发作期间大规模基因表达的变化，进行了转录组分析和代谢组学分析。在整个叶片组织中，与叶绿体有关的差异表达基因数量最多，而与氮和碳水化合物有关的代谢过程最多。五个基因代表与YCS发作期间转录下调相关的TPM（每百万转录本）的90％，其中包括PSII D1（PsbA）。这种差异表达与对光合作用的反馈调节作用一致。大规模的基因表达分析未揭示YCS发作期间叶糖积累的原因。有趣的是，中脉显示出最大的糖分积累，其次是有症状的椎板。从甘蔗转录组中表征⁺ -ATPase和H ^+-磷酸酶（H ⁺ -PPase）并分析其表达。显然有两类I H ⁺ -PPases簇，其中一个被上调，另一个被下调。尽管不太明显，但是对于H ⁺ -ATPases观察到类似的变化模式。出现视觉症状后，运输二糖的SWEET被下调，运输单糖的SWEET症状发展之前和之后的上调。SUT基因表达对YCS的发展反应最少。结果与通过韧皮部的光同化运动的减少相一致，从而导致叶片中蔗糖的积累。