Lindblom Stormy D, Wangeline Ami L, Valdez Barillas Jose R, Devilbiss Berthal, Fakra Sirine C, Pilon-Smits Elizabeth A H
Department of Biology, Colorado State University, Fort Collins, CO, United States.
Department of Biology, Laramie County Community College, Cheyenne, WY, United States.
Front Plant Sci. 2018 Aug 20;9:1213. doi: 10.3389/fpls.2018.01213. eCollection 2018.
Endophytes can enhance plant stress tolerance by promoting growth and affecting elemental accumulation, which may be useful in phytoremediation. In earlier studies, up to 35% elemental selenium (Se) was found in Se hyperaccumulator . Since Se can be produced by microbes, the plant Se was hypothesized to be microbe-derived. Here we characterize a fungal endophyte of named A2. It is common in seeds from natural seleniferous habitat containing 1,000-10,000 mg kg Se. We identified A2 as via 18S rRNA sequence analysis and morphological characterization. X-ray microprobe analysis of seeds that did or did not harbor , showed that both contained >90% organic seleno-compounds with C-Se-C configuration, likely methylselenocysteine and glutamyl-methylselenocysteine. The seed Se was concentrated in the embryo, not the seed coat. X-ray microprobe analysis of A2 in pure culture showed the fungus produced Se when supplied with selenite, but accumulated mainly organic C-Se-C compounds when supplied with selenate. A2 was completely resistant to selenate up to 300 mg L, moderately resistant to selenite (50% inhibition at ∼50 mg Se L), but relatively sensitive to methylselenocysteine and to Se extracted from (50% inhibition at 25 mg Se L). Four-week old seedlings derived from surface-sterilized seeds containing endophytic were up to threefold larger than seeds obtained from seeds not showing evidence of fungal colonization. When supplied with Se, the -colonized seedlings had lower shoot Se and sulfur levels than seedlings from uncolonized seeds. In conclusion, may contribute to the Se observed earlier in , and affect host growth and Se accumulation. A2 is sensitive to the Se levels found in its host's tissues, but may avoid Se toxicity by occupying low-Se areas (seed coat, apoplast) and converting plant Se to non-toxic Se. These findings illustrate the potential for hyperaccumulator endophytes to affect plant properties relevant for phytoremediation. Facultative endophytes may also be applicable in bioremediation and biofortification, owing to their capacity to turn toxic inorganic forms of Se into non-toxic or even beneficial, organic forms with anticarcinogenic properties.
内生菌可通过促进植物生长和影响元素积累来增强植物的胁迫耐受性，这在植物修复中可能具有重要作用。在早期研究中，在硒超富集植物中发现高达35%的元素硒（Se）。由于硒可由微生物产生，因此推测植物中的硒来源于微生物。在此，我们对一种名为A2的真菌内生菌进行了表征。它在天然富硒生境的种子中很常见，这些种子含硒量为1000 - 10000 mg/kg。通过18S rRNA序列分析和形态学特征鉴定，我们确定A2为[具体菌种名称未给出]。对含有或不含有[具体菌种名称未给出]的种子进行X射线微探针分析，结果表明两者都含有>90%的具有C - Se - C构型的有机硒化合物，可能是甲基硒代半胱氨酸和谷氨酰甲基硒代半胱氨酸。种子中的硒集中在胚中，而非种皮。对纯培养的A2进行X射线微探针分析表明，当提供亚硒酸盐时，该真菌能产生硒，但当提供硒酸盐时，主要积累有机C - Se - C化合物。A2对高达300 mg/L的硒酸盐具有完全抗性，对亚硒酸盐具有中等抗性（在约50 mg Se/L时50%受抑制），但对甲基硒代半胱氨酸和从[具体植物名称未给出]中提取的硒相对敏感（在25 mg Se/L时50%受抑制）。来自含有内生[具体菌种名称未给出]的表面消毒种子的四周龄[具体植物名称未给出]幼苗比未显示真菌定殖迹象的种子所产生的幼苗大三倍。当提供硒时，定殖有[具体菌种名称未给出]的幼苗地上部分的硒和硫水平低于未定殖种子的幼苗。总之，[具体菌种名称未给出]可能是早期在[具体植物名称未给出]中观察到的硒的来源，并影响宿主生长和硒积累。A2对其宿主组织中的硒水平敏感，但可能通过占据低硒区域（种皮、质外体）并将植物中的硒转化为无毒硒来避免硒毒性。这些发现说明了超富集植物内生菌在影响与植物修复相关的植物特性方面的潜力。兼性内生菌也可能适用于生物修复和生物强化，因为它们有能力将有毒的无机硒形式转化为具有抗癌特性的无毒甚至有益的有机形式。
