Dumigan Christopher R, Muileboom Jade, Gregory Jake, Shrestha Anuja, Hewedy Omar A, Raizada Manish N
Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
Front Plant Sci. 2021 Sep 16;12:660673. doi: 10.3389/fpls.2021.660673. eCollection 2021.
Plants can adapt to their surroundings by hosting beneficial bacteria that confer a selective advantage in stressful conditions. Endophytes are a class of beneficial bacteria that exist within the internal spaces of plants and many species can improve plant nitrogen use efficiency. Nitrogen is an essential plant macronutrient, and is often a limiting factor to plant growth, especially in cereal crops such as maize. Every year farmers apply over 100 million metric tonnes of synthetic nitrogen fertilizer to meet the growing demand for stable food crops. Breeding efforts in maize over the past several decades has focused heavily on yield in response to nitrogen inputs, and so may have selected against adaptations that allow plants to survive in nitrogen stressed conditions. Data suggests that our heavy dependence on synthetic nitrogen fertilizer is not sustainable in the long term, and so there is on-going research efforts to reduce and replace this currently essential part of modern agriculture. Bacteria that improve plant tolerance to nitrogen stressed environments would allow farmers to reduce the amount of fertilizer they apply. The selection of maize under high nitrogen conditions to create modern varieties may have caused the plant to lose these beneficial bacteria that allowed wild maize ancestors to thrive in low nitrogen soil. Here in this study, we examine the root and shoot microbiomes of the wild ancestor of all maize, Parviglumis, and an ancient Mexican landrace (Mixteco) from Oaxaca, the area of early maize diversification. Both of these maize genotypes have thrived for thousands of years with little to no nitrogen inputs and so we hypothesized that they host beneficial bacteria that allow them to thrive in nitrogen stressed conditions. We identified multiple root endophyte species from each ancient maize relative that increased the growth of annual ryegrass (model maize relative) under nitrogen starvation. Furthermore, research infers these strains were vertically transmitted to new generations of plants, potentially through seed, indicating selection pressure for Parviglumis and Mixteco to maintain them in their microbiome.
植物可以通过容纳有益细菌来适应周围环境，这些细菌在压力条件下赋予植物选择性优势。内生菌是一类存在于植物内部空间的有益细菌，许多种类的内生菌可以提高植物的氮利用效率。氮是植物必需的大量营养素，通常是植物生长的限制因素，尤其是在玉米等谷类作物中。每年，农民施用超过1亿吨的合成氮肥，以满足对稳定粮食作物不断增长的需求。在过去几十年里，玉米育种工作主要集中在氮肥投入下的产量，因此可能没有选择那些能让植物在氮胁迫条件下生存的适应性特征。数据表明，我们对合成氮肥的严重依赖从长远来看是不可持续的，因此目前正在进行研究，以减少和取代现代农业中这一目前必不可少的部分。能提高植物对氮胁迫环境耐受性的细菌将使农民减少化肥施用量。在高氮条件下选择玉米培育现代品种，可能导致这种植物失去了那些能让野生玉米祖先在低氮土壤中茁壮成长的有益细菌。在本研究中，我们研究了所有玉米的野生祖先小颖玉米以及来自瓦哈卡州（早期玉米多样化地区）的一个古老墨西哥地方品种（米斯特克玉米）的根和地上部微生物群。这两种玉米基因型在几乎没有或没有氮输入的情况下已经茁壮成长了数千年，因此我们推测它们含有能让它们在氮胁迫条件下茁壮成长的有益细菌。我们从每个古老玉米近缘种中鉴定出多种根内生菌物种，这些物种在氮饥饿条件下增加了一年生黑麦草（模式玉米近缘种）的生长。此外，研究推断这些菌株可能通过种子垂直传播到新一代植物中，这表明小颖玉米和米斯特克玉米在其微生物群中保留这些菌株存在选择压力。
