CAREER: Is phytohormone crosstalk the mechanism that predisposes drought-stressed conifers to bark beetle attack?

在过去的二十年里，北美西部的景观中发生了大规模的树皮甲虫爆发，对公共和私人土地产生了巨大的生态和经济影响。越来越多的证据表明，树木易受环境条件，特别是水分胁迫的影响。因此，区域性干旱可能为甲虫种群的快速增长创造条件，导致甲虫爆发和大规模森林死亡。然而，目前还不清楚为什么干旱胁迫下的树木更容易受到树皮甲虫的攻击-一种可能性是干旱胁迫抑制了树木的自我保护能力。虽然树木不像动物那样具有适应性免疫系统，但许多针叶树能够通过在树脂中产生有毒化学物质来识别和应对昆虫造成的细胞损伤。这些毒素的产生是由激素发出的信号，这些激素可能在甲虫攻击之前发生水分胁迫时功能受损。这项工作的目标是研究干旱胁迫如何干扰针叶树激素的产生和敏感性，并确定这种干扰是否是整个景观森林死亡率模式的基础。更广泛的影响包括STEM体验式学习的要素，对代表性不足的学生群体的指导，为学龄儿童开发新的教育材料，以及向广大受众进行科学传播。为了在生物和环境胁迫事件中生存下来，植物已经进化出生化信号传导途径，以适当地重新编程其表型以响应特定的挑战。虽然食草性昆虫的爆发往往是由环境胁迫事件，降低植物抵抗食草性的能力，这些相互作用的生理机制还不清楚。这是植物-昆虫相互作用领域的一个重要空白，因为它妨碍了我们将许多自然生态系统中的模式与过程联系起来的能力。对这种模式的一种基于过程的解释是，当环境压力先于生物挑战时，保守的激素受体会降低植物对防御激发子的敏感性。该项目将确定控制针叶树防御和开发新的理论，在化学生态学使用多个Engelmann云杉（云杉Engelmanni）人口，北美云杉树皮甲虫（Dendroctonus rufipennis），和甲虫相关的共生真菌（Leptographium abietinum）作为研究系统。该研究计划提出了四个相互关联的研究假设：（1）树木通过产生激素对不同类型的生物挑战做出不同的反应，（2）对这些激素的敏感性驱动化学和物理防御，（3）甲虫驱动的防御诱导降低了甲虫种群的表现，（4）环境压力抑制了树木对激素做出反应的能力，从而产生了适当的防御反应。解决这些集体的假设将阐明的信号机制，链接模式的生态系统干扰与基本的生理过程，并描述人口为基础的变化，激素敏感性和防御诱导在一个长寿的树种。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Large bark beetle outbreaks have occurred across the landscape of western North America during the past two decades with dramatic ecological and economic impacts for public and private lands. There is growing evidence that trees are predisposed to bark beetle attack by environmental conditions, especially water stress. Consequently, regional droughts could set the stage for rapid beetle population growth that leads to outbreaks and large-scale forest mortality. However, it remains unclear exactly why drought-stressed trees become more susceptible to bark beetle attack--one possibility is that drought stress inhibits the ability of trees to defend themselves. Although trees do not have an adaptive immune system like animals, many conifers are able to recognize and respond to cell damage from insects by producing toxic chemicals in their resin. Production of these toxins are signaled by hormones that may be functionally impaired when water stress occurs prior to beetle attack. The goal of this work is to examine how drought stress interferes with hormone production and sensitivity in conifers and determine whether this interference underlies patterns of forest mortality across landscapes. Broader impacts include elements of experiential learning in STEM, mentoring of underrepresented student populations, development of new educational materials for school-age children, and science communication to broad audiences. To survive biological and environmental stress events, plants have evolved biochemical signaling pathways to reprogram their phenotypes appropriately in response to specific challenges. Although insect herbivore outbreaks are often preceded by environmental stress events that reduce the ability of plants to resist herbivory, physiological mechanisms underlying these interactions are not understood. This is an important gap in the field of plant-insect interactions as it precludes our ability to connect pattern with process in many natural ecosystems. One process-based explanation for this pattern is that conserved hormone receptors drive reduced sensitivity of plants to defense elicitors when environmental stress precedes a biological challenge. This project will identify controls over conifer tree defenses and develop new theory in chemical ecology using multiple Engelmann spruce (Picea engelmanni) populations, the North American spruce bark beetle (Dendroctonus rufipennis), and a beetle-associated symbiotic fungus (Leptographium abietinum) as the study system. The research plan addresses four interconnected research hypotheses: (1) trees respond differently to different types of biotic challenge through producing hormones, (2) sensitivity to these hormones drives chemical and physical defenses, (3) hormone-driven defensive induction reduces beetle population performance, and (4) environmental stress suppresses the ability of trees to respond to hormones and thus mount an appropriate defensive response. Addressing these collective hypotheses will elucidate the signaling mechanisms that link patterns of ecosystem disturbance with basic physiological processes and describe population-based variation in hormone sensitivity and defensive induction in a long-lived tree species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.