The intensification of global soil salinization has seriously decreased crop yield. At the same time, the rapid increase in population has raised the demand for crop yields. Reasonable use of saline-alkali land and cultivation of salt-tolerant crops through transgenic technology becomes more important. Sweet sorghum [Sorghum bicolor (L.)], as an important energy crop, resists abiotic stress effectively. In our previous salt tolerance gene-screening experiment of sweet sorghum, it was found that applying calcium ions could alleviate salt stress of sweet sorghum to some extent. Therefore, 10 and 20 mM CaCl₂ were applied to explore the effect of exogenous calcium application on salt stress. Compared with the sweet sorghum treated by salt stress, the dry and fresh weight of the plants were significantly increased, and the content of malondialdehyde (MDA) was decreased after applying calcium ions. At the same time, diaminobenzidine and nitro blue tetrazolium chloride monohydrate staining results showed that the contents of H₂O₂ and O₂^−• in the plants after calcium application were lower than those only treated with salt stress. To investigate the regulation mechanism of exogenous calcium application alleviating salt stress, RNA-seq analysis was performed using libraries established in Roma roots under normal and NaCl treatment. Combined with Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes analysis, we found that calcium-related genes were more involved in the oxidation-reduction process and carbohydrate metabolism pathway. Among all differentially expressed genes, 12 known functional genes were further explored based on functional annotations and existing studies. To detect whether these 12 genes are related to salt response, we treated the Arabidopsis mutants of their homologous genes with 150 mM NaCl for 7 days. Among them, atglr3.5, atgad4, atiqm4, atglr2.8 and annat7 showed worse growth, lower survival rate and higher MDA content than WT under salt stress. This indicates that applying exogenous calcium can affect the expression of SbGR3.4, SbGADX1, SbIQM4, SbGR2.8 and SbAnnD7, which can regulate the expression of genes related to the lignin degradation, absorption of NH₄⁺, and ubiquitination-proteasome pathway, energy metabolism and cleaning of ROS accumulation in sweet sorghum under salt stress, so as to enhance the salt tolerance of plants.

中文翻译：

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外源补钙提高甜高粱幼苗耐盐性

全球土壤盐渍化加剧，严重降低了农作物产量。与此同时，人口的快速增长也提高了对农作物产量的需求。合理利用盐碱地，通过转基因技术种植耐盐作物变得更加重要。甜高粱[ Sorghum bicolor (L.)]作为重要的能源作物，能有效抵抗非生物胁迫。在我们之前的甜高粱耐盐基因筛选实验中，发现施用钙离子可以在一定程度上缓解甜高粱的盐胁迫。因此，10 和 20 mM CaCl ₂用于探讨外源钙应用对盐胁迫的影响。与盐胁迫处理的甜高粱相比，施用钙离子后植株干鲜重明显增加，丙二醛（MDA）含量降低。同时，二氨基联苯胺和硝基蓝四唑氯化物一水合物染色结果表明H ₂ O ₂和O ₂ ^-•钙施用后的植物中的含量低于仅用盐胁迫处理的植物。为了研究外源钙应用缓解盐胁迫的调节机制，使用在正常和 NaCl 处理下在罗马根中建立的文库进行 RNA-seq 分析。结合Gene Ontology和Kyoto Encyclopedia of Genes and Genomes分析，我们发现钙相关基因更多地参与了氧化还原过程和碳水化合物代谢途径。在所有差异表达基因中，基于功能注释和现有研究进一步探索了12个已知功能基因。为了检测这 12 个基因是否与盐反应有关，我们用 150 mM NaCl 处理其同源基因的拟南芥突变体 7 天。其中，atglr3。5、atgad4、atiqm4、atglr2。8和annat7 在盐胁迫下表现出比 WT 更差的生长、更低的存活率和更高的 MDA 含量。这说明外源性钙的应用可以影响SbGR3的表达。4、SbGADX1、SbIQM4、SbGR2。8和SbAnnD7，可调节木质素降解、NH ₄ ^{+吸收相关基因的表达}, 泛素化-蛋白酶体途径, 能量代谢和盐胁迫下甜高粱 ROS 积累的清除, 从而增强植物的耐盐性。