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

在过去的二十年里，北美西部地区发生了大规模的树皮甲虫暴发，对公共和私人土地造成了巨大的生态和经济影响。越来越多的证据表明，树木容易受到环境条件，特别是水分胁迫的攻击。因此，地区性干旱可能为甲虫种群的快速增长奠定基础，从而导致疫情暴发和大规模森林死亡。然而，目前还不清楚为什么干旱压力下的树木更容易受到树皮甲虫的攻击--一种可能性是干旱压力抑制了树木自我防御的能力。尽管树木没有动物那样的适应性免疫系统，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对细胞的破坏。这些毒素的产生是由荷尔蒙发出信号的，当甲虫攻击之前发生水分胁迫时，荷尔蒙可能会功能受损。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不同景观森林死亡模式的基础。更广泛的影响包括STEM的体验式学习要素、对代表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传播科学。为了在生物和环境胁迫事件中生存下来，植物进化了生化信号通路，以适当地重新编程它们的表型，以响应特定的挑战。虽然昆虫食草动物的暴发通常发生在环境胁迫事件之前，这些事件降低了植物抵抗食草性的能力，但这些相互作用的生理机制尚不清楚。这是植物-昆虫相互作用领域的一个重要缺口，因为它排除了我们在许多自然生态系统中将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，当环境胁迫先于生物挑战时，保守的激素受体导致植物对防御激发子的敏感度降低。该项目将以多个恩格尔曼云杉(Picea Engelmanni)种群、北美云杉树皮甲虫(Dendroctonus Rufipennis)和与甲虫相关的共生真菌(Leptograph Ium Abietum)为研究系统，确定针叶树防御的控制措施，并发展新的化学生态学理论。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)激素驱动的防御诱导降低甲虫的种群表现，(4)环境胁迫抑制树木对激素的反应能力，从而产生适当的防御反应。解决这些集体假设将阐明将生态系统干扰模式与基本生理过程联系起来的信号机制，并描述长寿树种在激素敏感性和防御诱导方面的基于种群的变化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.