Evolution of drought tolerance and defense: dependence of tradeoffs on mechanism, environment and defense switching
Evolution of drought tolerance and defense: dependence of tradeoffs on mechanism, environment and defense switching
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DOI：
10.1111/j.2007.0030-1299.16111.x
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发表时间：
2008-02-01
期刊：
影响因子：
3.4
通讯作者：
Siemens, David H.
中科院分区：
文献类型：
--
作者：
Haugen, Riston;Steffes, Lexi;Siemens, David H.
植物在压力环境中进化出对食草动物和病原体的防御能力；然而，对其他环境应激源进化出耐受性的植物可能具有妥协的防御能力。这种涉及防御的权衡可能取决于有限的资源或其他压力环境；然而，压力环境对防御表达的影响可能因不同的基因类型而不同(GxE)。为了验证这些预测，我们在两个遗传变异水平上研究了干旱胁迫耐性和防御的遗传变异和协变：在密切相关的物种之间和内部。我们在一个生长室内的试验性干旱压力梯度上完成了这项工作，这些物种的耐旱性可能存在遗传差异。与预测明显相反的是，来自较低和较干燥海拔的十字花科植物Boechera holboellii的固有生长速度较慢，相应地防御性硫代葡萄糖苷的总浓度也高于来自较高海拔的近缘物种B.strata。因此，B.holboellii既耐旱又被防御；然而，最优化理论确实预测了防御和生长之间的权衡。不同物种在缺水对硫代葡萄糖苷生产的直接影响上的差异并没有掩盖生长或防御之间的权衡。B.holboellii也可能对专业食草性小菜蛾更具抵抗力；这一趋势不太明显，因为它取决于植物的发育和缺水条件。在较细的遗传变异尺度上，家系和自然自交系之间的耐旱性存在显著差异，包括固有生长量、干旱处理下的生长反应标准、地上部水势和蒸腾速率。在抗性和蒸腾速率或硫代葡萄糖苷和生长速率之间的遗传相关性中，也发现了在B.strata中进行权衡的证据。在这些更细微的遗传变异尺度上没有检测到GxE，尽管有时权衡取决于干旱条件。干旱胁迫的直接影响导致了对伤害的抗性和耐受性之间的明显的可塑性转换，这可能是一种避免成本的机制，因为权衡从来不涉及对伤害的容忍。因此，当耐旱性表现为内在生长速度缓慢时，植物也可能具有相对较高的防御水平，特别是在压力大的环境中。否则，防御可能会受到干旱应对机制的影响，尽管塑料转换为成本较低的防御可能会缓解压力环境中的限制。
Plants evolve defenses against herbivores and pathogens in stressful environments; however, plants that evolve tolerances to other environmental stressors may have compromised defenses. Such tradeoffs involving defenses may depend on limited resources or otherwise stressful environments; however, the effect of stressful environments on defense expression might be different for different genotypes (GxE). To test these predictions, we studied genetic variation and co-variation of drought stress tolerance and defenses at two levels of genetic variation: between and within closely related species. We did this across an experimental drought stress gradient in a growth room for species for which genetic variation in drought tolerance was likely. In apparent contrast to predictions, the species Boechera holboellii (Brassicaceae) from lower and dryer elevations had slower inherent growth rates and correspondingly higher total defensive glucosinolate concentrations than the closely related species B. stricta from higher elevations. Thus, B. holboellii was both drought tolerant and defended; however, optimality theory does predict tradeoffs between defense and growth. Differences between species in the direct effect of water deficiency on glucosinolate production did not obscure the grow-or-defend tradeoff. B. holboellii may also have been more resistant to the specialist herbivore Plutella xylostella; a trend that was less clear because it depended on plant development and water deficient conditions. At finer scales of genetic variation, there was significant variation among families and naturally occurring inbred lines of B. stricta in drought tolerance measured as inherent growth, the reaction norm of growth across drought treatments, shoot water potential, and transpiration rates. Evidence for tradeoffs was also found within B. stricta in genetic correlations between resistance and transpiration rates, or glucosinolates and growth rates. No GxE was detected at these finer scales of genetic variation, although sometimes the tradeoff was dependent on drought conditions. Direct effects of drought stress resulted in an apparent plastic switch between resistance and tolerance to damage, which might be a cost avoidance mechanism because tradeoffs never involved tolerance to damage. Thus, when drought tolerance is manifest as slow inherent growth rates, plants may also have relatively high defense levels, especially in stressful environments. Otherwise, defenses may be compromised by drought-coping mechanisms, although plastic switches to less costly defenses may alleviate constraints in stressful environments.