Agorsor Israel D K, Kagel Brian T, Danna Cristian H
Department of Biology, University of Virginia, Charlottesville, VA 22904, USA.
Department of Molecular Biology & Biotechnology, School of Biological Sciences, College of Agriculture & Natural Sciences, University of Cape Coast, UC, Cape Coast P.O. Box 5007, Ghana.
Plants (Basel). 2023 Jan 12;12(2):371. doi: 10.3390/plants12020371.
The root microbiome structure ensures optimal plant host health and fitness, and it is, at least in part, defined by the plant genotype. It is well documented that root-secreted amino acids promote microbial chemotaxis and growth in the rhizosphere. However, whether the plant-mediated re-uptake of amino acids contributes to maintaining optimal levels of amino acids in the root exudates, and, in turn, microbial growth and metabolism, remains to be established. Here, we show that Lysine-Histidine Transporter-1 (LHT1), an amino acid inward transporter expressed in roots, limits the growth of the plant-growth-promoting bacteria WCS417r ( WCS417r). The amino acid profiling of the mutant root exudates showed increased levels of glutamine, among other amino acids. Interestingly, exudates or Gln-supplemented wild-type exudates enhance WCS417r growth. However, despite promoting bacterial growth and robust root colonization, exudates and Gln-supplemented wild-type exudates inhibited plant growth in a WCS417r-dependent manner. The transcriptional analysis of defense and growth marker genes revealed that plant growth inhibition was not linked to the elicitation of plant defense but likely to the impact of WCS417r amino acids metabolism on auxin signaling. These data suggest that an excess of amino acids in the rhizosphere impacts WCS417r metabolism, which, in turn, inhibits plant growth. Together, these results show that LHT1 regulates the amino-acid-mediated interaction between plants and WCS417r and suggest a complex relationship between root-exuded amino acids, root colonization by beneficial bacteria, bacterial metabolism, and plant growth promotion.
根系微生物群结构确保植物宿主的健康和适应性达到最佳状态，并且至少部分地由植物基因型决定。有充分的文献记载，根系分泌的氨基酸可促进微生物在根际的趋化作用和生长。然而，植物介导的氨基酸再吸收是否有助于维持根系分泌物中氨基酸的最佳水平，进而影响微生物的生长和代谢，仍有待确定。在这里，我们表明，赖氨酸-组氨酸转运蛋白-1（LHT1）是一种在根中表达的氨基酸内向转运蛋白，它限制了促进植物生长的细菌WCS417r（WCS417r）的生长。突变体根系分泌物的氨基酸谱分析表明，除其他氨基酸外，谷氨酰胺水平有所增加。有趣的是，突变体根系分泌物或添加了谷氨酰胺的野生型根系分泌物可促进WCS417r的生长。然而，尽管促进了细菌生长和强大的根部定殖，但突变体根系分泌物和添加了谷氨酰胺的野生型根系分泌物以WCS417r依赖的方式抑制了植物生长。对防御和生长标记基因的转录分析表明，植物生长抑制与植物防御的激发无关，而可能与WCS417r氨基酸代谢对生长素信号传导的影响有关。这些数据表明，根际中过量的氨基酸会影响WCS417r的代谢，进而抑制植物生长。总之，这些结果表明LHT1调节植物与WCS417r之间由氨基酸介导的相互作用，并表明根系分泌的氨基酸、有益细菌的根部定殖、细菌代谢和植物生长促进之间存在复杂的关系。
