Table_8_Physio-biochemical and transcriptomic analysis of Bacillus amyloliquefaciens PG-4-induced salt stress tolerance in Macrotyloma uniflorum.DOCX

IntroductionMacrotyloma uniflorum is an important legume fodder crop and green fertilizer. Salinity impedes plant growth and productivity of legume crops by disrupting the ionic and osmotic balance and hormonal regulation. Plant growth-promoting rhizobacteria (PGPR) are rhizosphere bacteria that contribute to the improvement of plant growth through diverse physiological mechanisms.
MethodsIn this study, the growth promoting characteristics of the isolated strain Bacillus amyloliquefaciens PG-4 were analyzed, and to further investigated the possible mechanism of PG-4 in mitigating the damage caused by salt stress in M. uniflorum plants through pot experiments.
ResultsIn presence of different salt levels, PG-4 showed a high potentiality to produce several plant growth promoting metabolites such as NH3, siderophore, 1-aminocyclopropane-1-carboxylic acid deaminase (ACC-deaminase), and hydrolytic enzymes. Inoculation of the PG-4 significantly enhanced plant tolerance to salt stress, as demonstrated by promotion of plant growth (shoot and root biomass) under salt stress condition. Furthermore, PG-4 improved salt tolerance of Macrotyloma uniflorum seedlings by affecting the antioxidant enzymes including peroxidase (POD) and superoxide dismutase (SOD), by increasing the levels of proline, soluble sugars and chlorophyll. Treatment with PG-4 increased the K+ content while decreased the Na+ concentration level under salt stress. Transcriptomic analysis revealed 5525 genes were differentially expressed (PG-4-inoculated versus non-inoculated samples) at 0 mM NaCl, of which 3277 were upregulated and 2248 downregulated, while 1298 genes were differentially expressed at 100 mM NaCl, of which 819 were upregulated and 479 were downregulated. GO and KEGG enrichment analyses showed that these DEGs were significantly enriched in several terms and pathways mainly involved in the regulation of the cellular redox state, cell wall modification, metabolic adjustments, hemoglobin, biosynthesis of secondary metabolites and plant hormone signal transduction.
DiscussionThese data showed that Bacillus amyloliquefaciens PG-4 significantly enhance salt stress tolerance in Macrotyloma uniflorum plants during salt stress conditions. Therefore, the results may be useful for explaining the mechanism by which PGPR inoculation regulates the salt tolerance of crops.

引言：单花扁豆（Macrotyloma uniflorum）是一类重要的豆科饲用作物与绿肥作物。盐胁迫可通过破坏离子与渗透稳态、干扰激素调控，抑制豆科作物的生长及产量形成。植物促生根际细菌（Plant growth-promoting rhizobacteria, PGPR）是定殖于植物根际的一类细菌，可通过多种生理途径促进植物生长发育。
材料与方法：本研究首先分析了分离获得的解淀粉芽孢杆菌（Bacillus amyloliquefaciens）PG-4菌株的促生特性，进而通过盆栽试验，深入探究PG-4缓解盐胁迫对单花扁豆植株造成损伤的潜在作用机制。
结果：在不同盐浓度梯度条件下，PG-4菌株展现出较强的合成多种植物促生代谢物的能力，包括氨（NH3）、铁载体、1-氨基环丙烷-1-羧酸脱氨酶（ACC脱氨酶）以及水解酶。PG-4接种可显著提升植株的盐胁迫耐受性，具体表现为盐胁迫环境下植株生长（地上部与根部生物量）得到显著促进。此外，PG-4可通过调控过氧化物酶（peroxidase, POD）、超氧化物歧化酶（superoxide dismutase, SOD）等抗氧化酶活性，提升脯氨酸、可溶性糖及叶绿素含量，从而增强单花扁豆幼苗的耐盐性。盐胁迫条件下经PG-4处理的植株，其钾离子（K+）含量显著升高，而钠离子（Na+）浓度显著降低。转录组分析结果显示，在0 mM NaCl处理组中，接种PG-4与未接种的样本间共鉴定出5525个差异表达基因（differentially expressed genes, DEGs），其中3277个基因上调表达、2248个基因下调表达；在100 mM NaCl处理组中，共鉴定出1298个差异表达基因，其中819个基因上调表达、479个基因下调表达。基因本体（Gene Ontology, GO）与京都基因与基因组百科全书（Kyoto Encyclopedia of Genes and Genomes, KEGG）富集分析表明，这些差异表达基因显著富集于多个条目与通路，主要涉及细胞氧化还原稳态调控、细胞壁修饰、代谢调节、植物血红蛋白功能、次生代谢产物生物合成以及植物激素信号转导。
讨论：上述研究结果证实，解淀粉芽孢杆菌PG-4可在盐胁迫环境下显著提升单花扁豆植株的盐胁迫耐受性。因此，本研究结果可为阐明PGPR接种调控作物耐盐性的内在分子机制提供重要的理论参考。