Department of Biology, The Norwegian University of Science and Technology, Realfagbygget, 7491 Trondheim, Norway.
BMC Genomics. 2011 Aug 19;12:423. doi: 10.1186/1471-2164-12-423.
Phloem-feeding aphids deprive plants of assimilates, but mostly manage to avoid causing the mechanical tissue damage inflicted by chewing insects. Nevertheless, jasmonate signalling that is induced by infestation is important in mediating resistance to phloem feeders. Aphid attack induces the jasmonic acid signalling pathway, but very little is known about the specific impact jasmonates have on the expression of genes that respond to aphid attack.
We have evaluated the function that jasmonates have in regulating Arabidopsis thaliana responses to cabbage aphid (Brevicoryne brassicae) by conducting a large-scale transcriptional analysis of two mutants: aos, which is defective in jasmonate production, and fou2, which constitutively induces jasmonic acid biosynthesis. This analysis enabled us to determine which genes' expression patterns depend on the jasmonic acid signalling pathway. We identified more than 200 genes whose expression in non-challenged plants depended on jasmonate levels and more than 800 genes that responded differently to infestation in aos and fou2 plants than in wt. Several aphid-induced changes were compromised in the aos mutant, particularly genes connected to regulation of transcription, defence responses and redox changes. Due to jasmonate-triggered pre-activation of fou2, its transcriptional profile in non-challenged plants mimicked the induction of defence responses in wt. Additional activation of fou2 upon aphid attack was therefore limited. Insect fitness experiments revealed that the physiological consequences of fou2 mutation contributed to more effective protection against B. brassicae. However, the observed resistance of the fou2 mutant was based on antibiotic rather than feeding deterrent properties of the mutant as indicated by an analysis of aphid feeding behaviour.
Analysis of transcriptional profiles of wt, aos and fou2 plants revealed that the expression of more than 200 genes is dependent on jasmonate status, regardless of external stimuli. Moreover, the aphid-induced response of more than 800 transcripts is regulated by jasmonate signalling. Thus, in plants lacking jasmonates many of the defence-related responses induced by infestation in wt plants are impaired. Constant up-regulation of jasmonate signalling as evident in the fou2 mutant causes reduction in aphid population growth, likely as a result of antibiotic properties of fou2 plants. However, aos mutation does not seem to affect aphid performance when the density of B. brassicae populations on plants is low and aphids are free to move around.
吸食韧皮部的蚜虫会剥夺植物的同化产物，但它们大多设法避免造成咀嚼式昆虫造成的机械组织损伤。然而，被侵害后诱导的茉莉酸信号在介导对韧皮部食者的抗性方面很重要。蚜虫的攻击会诱导茉莉酸信号通路，但人们对茉莉酸对响应蚜虫攻击的基因表达的具体影响知之甚少。
我们通过对两个突变体（aos，其茉莉酸产生有缺陷；和 fou2，其组成性诱导茉莉酸生物合成）进行大规模转录分析，评估了茉莉酸在调节拟南芥对甘蓝蚜（Brevicoryne brassicae）反应中的作用。这项分析使我们能够确定哪些基因的表达模式依赖于茉莉酸信号通路。我们鉴定了 200 多个在非胁迫植物中表达依赖于茉莉酸水平的基因，以及 800 多个在 aos 和 fou2 植物中对侵染的反应与 wt 植物不同的基因。在 aos 突变体中，几个蚜虫诱导的变化受到损害，特别是与转录调控、防御反应和氧化还原变化有关的基因。由于茉莉酸触发了 fou2 的预先激活，其在非胁迫植物中的转录谱模拟了 wt 中防御反应的诱导。因此，在受到蚜虫攻击后， fou2 的进一步激活受到限制。昆虫适应性实验表明， fou2 突变的生理后果有助于更有效地保护拟南芥免受 B. brassicae 的侵害。然而，正如对蚜虫取食行为的分析所示， fou2 突变体的观察到的抗性基于突变体的抗生素而不是取食抑制特性。
wt、aos 和 fou2 植物的转录谱分析表明，200 多个基因的表达依赖于茉莉酸状态，而与外部刺激无关。此外，茉莉酸信号调节了 800 多个转录物的诱导的蚜虫反应。因此，在缺乏茉莉酸的植物中，wt 植物中因侵染而诱导的许多防御相关反应受损。在 fou2 突变体中明显的茉莉酸信号的持续上调导致蚜虫种群生长减少，可能是由于 fou2 植物的抗生素特性所致。然而，当甘蓝蚜种群密度较低且蚜虫可以自由移动时， aos 突变似乎不会影响蚜虫的表现。
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