Differentiation of rhizosphere fungal assemblages by host ploidy level in mixed-ploidy Larrea tridentata populations

Polyploidy—whole genome duplication—is common in plants. Studies over the
last several decades have documented numerous mixed-ploidy populations.
Whether arising via recurrent whole genome duplication events within a
population, or from secondary contact, the persistence of mixed
populations is possible by niche differentiation. Specifically, one
mechanism facilitating ploidy co-occurrence is microbially-mediated niche
differentiation (MMND), wherein cytotypes occupy different niches via
interactions with different sets of microbes. Inherently cryptic, MMND is
underexplored in polyploid plant populations. Here, we search for evidence
of MMND in creosotebush (Larrea tridentata), a dominant desert shrub of
the southwestern U.S. and northern Mexico. We sequenced root-associated
fungal taxa in soil diploid, autotetraploid, and autohexaploid plants
growing in two naturally-occurring mixed-cytotype populations. Within
populations, we found substantial fungal assemblage overlap across host
plant cytotypes. However, using indicator species analysis, we identified
some fungi that are differentiated by host plant cytotype, satisfying a
precondition for MMND. Future study is needed to determine the degree of
niche differentiation conferred, if any, and whether the identified fungi
play a role in the long-term persistence of multiple cytotypes within
populations.

多倍性——即全基因组复制——在植物中十分常见。近数十年来的研究已记录了大量多倍型混合种群。这类混合种群既可能源于种群内反复发生的全基因组复制事件，也可能源自次生接触，而生态位分化可维持其存续。具体而言，促进多倍型共存的一种机制是微生物介导的生态位分化（microbially-mediated niche differentiation, MMND）：不同胞型宿主通过与不同类群微生物互作，占据不同生态位。由于其本质上具有隐蔽性，MMND在多倍体植物种群中的研究仍有待深入。本研究以美国西南部及墨西哥北部的优势荒漠灌木——三齿拉雷亚灌木（Larrea tridentata）为对象，探寻其MMND相关证据。我们对两个自然形成的多胞型混合种群中，生长于土壤内的二倍体、同源四倍体及同源六倍体宿主植物的根关联真菌类群进行了测序。在种群内部，不同宿主胞型的真菌群落存在大量重叠。不过，通过指示物种分析，我们鉴定出了部分随宿主胞型呈现差异化分布的真菌类群，这满足了MMND存在的前提条件。未来仍需开展研究，以明确（若存在的话）此类真菌介导的生态位分化程度，以及所鉴定出的真菌是否对种群内多胞型的长期存续发挥作用。