Fuchs Benjamin, Damerau Annelie, Yang Baoru, Muola Anne
Biodiversity Unit, University of Turku, Turku FI-20014, Finland.
Food Sciences, Department of Life Technologies, University of Turku, Turku FI-20014, Finland.
Ann Bot. 2024 Dec 31;134(6):993-1002. doi: 10.1093/aob/mcae133.
Epichloë endophytes are vertically transmitted via grass seeds and chemically defend their hosts against herbivory. Endophyte-conferred plant defence via alkaloid biosynthesis might occur independently of costs for host plant growth. However, fitness consequences of endophyte-conferred defence and transgenerational effects on herbivore resistance of progeny plants are rarely studied. The aim of this study was to test whether severe defoliation in mother plants affects their seed production, seed germination rate and the endophyte-conferred resistance of progeny plants.
In a field study, we tested the effects of defoliation and endophyte symbiosis (Epichloë uncinata) on host plant (Festuca pratensis) performance, loline alkaloid concentrations in leaves and seeds, seed biomass and seed germination rates. In a subsequent greenhouse study, we challenged the progeny of the plants from the field study to aphid herbivory and tested whether defoliation of mother plants affects endophyte-conferred resistance against aphids in progeny plants.
Defoliation of the mother plants resulted in a reduction of alkaloid concentrations in leaves and elevated the alkaloid concentrations in seeds when compared with non-defoliated endophyte-symbiotic plants. Viability and germination rate of seeds of defoliated endophyte-symbiotic plants were significantly lower compared with those of non-defoliated endophyte-symbiotic plants and endophyte-free (defoliated and non-defoliated) plants. During 6 weeks of growth, seedlings of defoliated endophyte-symbiotic mother plants had elevated alkaloid concentrations, which was negatively correlated with aphid performance.
Endophyte-conferred investment in higher alkaloid levels in seeds, elicited by defoliation, provided protection from herbivores in progenies during the first weeks of plant establishment. Better protection of seeds via high alkaloid concentrations was negatively correlated with seed germination, indicating a trade-off between protection and viability.
内生真菌通过草种子进行垂直传播，并在化学层面保护宿主免受食草动物侵害。内生真菌通过生物碱生物合成赋予植物的防御作用可能独立于宿主植物生长的成本。然而，内生真菌介导的防御对植物适应性的影响以及对后代植物抗食草动物能力的跨代效应鲜有研究。本研究的目的是测试母本植物的严重去叶处理是否会影响其种子产量、种子发芽率以及后代植物中内生真菌介导的抗性。
在一项田间研究中，我们测试了去叶处理和内生真菌共生（Epichloë uncinata）对宿主植物（高羊茅）性能、叶片和种子中洛林生物碱浓度、种子生物量和种子发芽率的影响。在随后的温室研究中，我们用蚜虫取食挑战田间研究中植物的后代，并测试母本植物的去叶处理是否会影响后代植物中内生真菌介导的对蚜虫抗性。
与未去叶的内生真菌共生植物相比，母本植物的去叶处理导致叶片中生物碱浓度降低，种子中生物碱浓度升高。去叶的内生真菌共生植物的种子活力和发芽率显著低于未去叶的内生真菌共生植物和无内生真菌（去叶和未去叶）的植物。在生长的6周内，去叶的内生真菌共生母本植物的幼苗生物碱浓度升高，这与蚜虫的生长表现呈负相关。
去叶处理引发的内生真菌在种子中积累更高生物碱水平的投入，在植物建立的最初几周为后代提供了免受食草动物侵害的保护。通过高生物碱浓度更好地保护种子与种子发芽呈负相关，表明在保护和活力之间存在权衡。
