State Key Laboratory of Tree Genetics and Breeding, Forestry Institute of New Technology, Chinese Academy of Forestry, Beijing, China.
State Key Laboratory of Tree Genetics and Breeding, Institute of Forestry, Chinese Academy of Forestry, Beijing, China.
Sci Rep. 2019 Jul 12;9(1):10111. doi: 10.1038/s41598-019-46635-5.
Carbon starvation is the current leading hypothesis of plant mortality mechanisms under drought stress; recently, it is also used to explain tree die-off in plant diseases. However, the molecular biology of the carbon starvation pathway is unclear. Here, using a punch inoculation system, we conducted transcriptome and physiological assays to investigate pathogen response in poplar stems at the early stages of Botryosphaeria and Valsa canker diseases. Transcriptome assays showed that the majority of differentially expressed genes (DEGs) in stem phloem and xylem, such as genes involved in carbon metabolism and transportation, aquaporin genes (in xylem) and genes related to the biosynthesis of secondary metabolites and the phenylpropanoid pathway (related to lignin synthesis), were downregulated at 7 days after inoculation (DAI). Results also showed that the expression of the majority of disease-resistance genes upregulated in poplar stems, which may be connected with the downregulation expression of the majority of WRKY family genes. Physiological assays showed that transpiration rate decreased but WUE (water use efficiency) increased the 3 and 7 DAI, while the net photosynthetic rate decreased at 11 DAI in Botryosphaeria infected poplars (ANOVA, P < 0.05). The NSC (non-structural carbohydrates) content assays showed that the soluble sugar content of stem phloem samples increased at 3, 7, and 11 DAI that might due to the impede of pathogen infection. However, soluble sugar content of stem xylem and root samples decreased at 11 DAI; in contrast, the starch content unchanged. Therefore, results revealed a chronological order of carbon related molecular and physiological performance: declination of genes involved in carbon and starch metabolism first (at least at 7 DAI), declination of assimilation and carbon reserve (at 11 DAI) second. Results implied a potential mechanism that affects the host carbon reserve, by directly inhibiting the expression of genes involved in carbon metabolism and transport.
碳饥饿是目前干旱胁迫下植物死亡机制的主要假说；最近，它也被用于解释植物疾病中的树木死亡。然而，碳饥饿途径的分子生物学尚不清楚。在这里，我们使用打孔接种系统，在杨树茎部早期的胶孢炭疽病和溃疡病菌感染过程中，通过转录组和生理测定来研究病原体的反应。转录组测定表明，韧皮部和木质部中大多数差异表达基因（DEGs），如参与碳代谢和运输的基因、木质部中的水通道蛋白基因和与次生代谢物和苯丙烷途径（与木质素合成有关）合成相关的基因，在接种后 7 天（DAI）下调。结果还表明，杨树茎中大多数上调的抗病基因表达上调，这可能与大多数 WRKY 家族基因的下调表达有关。生理测定表明，蒸腾速率在第 3 和 7 DAI 下降，但水分利用效率（WUE）增加，而在第 11 DAI 时，感染胶孢炭疽病的杨树净光合速率下降（ANOVA，P < 0.05）。非结构性碳水化合物（NSC）含量测定表明，茎韧皮部样本中的可溶性糖含量在第 3、7 和 11 DAI 增加，这可能是由于病原体感染受阻。然而，在第 11 DAI 时，茎木质部和根样本中的可溶性糖含量下降；相比之下，淀粉含量不变。因此，结果揭示了与碳相关的分子和生理表现的时间顺序：首先是参与碳和淀粉代谢的基因下降（至少在第 7 DAI），其次是同化和碳储备下降（在第 11 DAI）。结果表明，通过直接抑制参与碳代谢和运输的基因的表达，影响宿主碳储备的潜在机制。
