Elevated production of reactive oxygen species is related to host plant resistance to sugarcane aphid in sorghum.

Sugarcane aphid (Melanaphis sacchari) is a phloem-feeding insect that severely affects the growth and productivity of sorghum and other related crops. While a growing body of knowledge is accumulating regarding plant, and insect interactions, the role of reactive oxygen species (ROS) against aphid infestation in sorghum has not been established yet. Here, the involvement of H2O2 and ROS detoxification enzymes in host plant resistance to sugarcane aphid in sorghum was demonstrated. The H2O2 accumulation and expression patterns of selected ROS scavenging enzymes including ascorbate peroxidase (APX), glutathione S transferase (GST), superoxide dismutase (SOD), and catalase (CAT) in response to sugarcane aphid infestation at 3, 6, 9, and 12 days post infestation (dpi) in resistant (Tx2783) and susceptible (Tx7000) sorghum genotypes were assessed, respectively. A significant increase in H2O2 accumulation was observed in resistant genotypes at all time points studied as compared to susceptible plants. Furthermore, gene expression analysis revealed that in responding to attack by sugarcane aphid, antioxidant genes were induced in both genotypes, but much stronger in the resistant line. Furthermore, aphid survival and fecundity were significantly inhibited in resistant plants compared to susceptible plants. Taken together, our results suggest that the elevated accumulation of H2O2 and the strong upregulation of the antioxidant genes in sorghum may have contributed to host plant resistance in Tx2783 against sugarcane aphid but the weak expression of those antioxidant genes in Tx7000 resulted in the failure of attempting defense against sugarcane aphid. This report also provides the experimental evidence for the role of ROS involvement in the early defensive response to an attack by sugarcane aphid in sorghum.

甘蔗蚜（Melanaphis sacchari）是一类以韧皮部汁液为食的昆虫，可严重影响高粱及其他相关作物的生长与产量。尽管目前关于植物与昆虫互作的研究积累日益丰厚，但高粱体内活性氧（reactive oxygen species, ROS）抵御蚜虫侵染的具体作用尚未明确。本研究证实了过氧化氢（H₂O₂）与ROS解毒酶在高粱宿主抵御甘蔗蚜的抗性机制中的参与作用。本研究分别检测了抗蚜（Tx2783）与感蚜（Tx7000）两种高粱基因型，在甘蔗蚜侵染后3、6、9、12天（dpi）时的H₂O₂积累水平，以及筛选得到的ROS清除酶——包括抗坏血酸过氧化物酶（ascorbate peroxidase, APX）、谷胱甘肽S-转移酶（glutathione S transferase, GST）、超氧化物歧化酶（superoxide dismutase, SOD）和过氧化氢酶（catalase, CAT）——的表达模式。相较于感蚜植株，抗蚜基因型在所有检测时间点的H₂O₂积累量均显著升高。此外，基因表达分析结果显示，两种基因型在遭遇甘蔗蚜侵染时，抗氧化基因均被诱导激活，但抗蚜品系的诱导程度显著更强。同时，与感蚜植株相比，抗蚜植株上的蚜虫存活率与繁殖力均受到显著抑制。综上，本研究结果表明，高粱体内H₂O₂积累量的提升与抗氧化基因的强上调表达，可能是Tx2783具备抗甘蔗蚜宿主抗性的核心原因；而Tx7000中抗氧化基因表达水平较弱，则导致其无法有效抵御甘蔗蚜侵染。本研究同时为ROS参与高粱早期抵御甘蔗蚜侵染的防御反应提供了实验依据。