Abstract：
Due to the chelation of phosphorus in the soil, it becomes unavailable for plant growth and development. The mechanisms by which phosphorus-solubilizing bacteria activate immobilized phosphorus to promote the growth and development of woody plants, as well as the intrinsic molecular mechanisms, are not clear. Through the analysis of microbial communities in the rhizosphere 16S V3-V4 and a homologous gene encoding microbial alkaline phosphomonoesterase (phoD) in phosphate-efficient (PE) and phosphate-inefficient apple rootstocks, it was found that PE significantly enriched beneficial rhizobacteria. The best phosphorus-solubilizing bacteria, Bacillus sp. strain 7DB1 (B2), was isolated, purified, and identified from the rhizosphere soil of PE rootstocks. Incubating with Bacillus B2 into the rhizosphere of apple rootstocks significantly increased the soluble phosphorus and flavonoid content in the rhizosphere soil. Simultaneously, this process stimulates the root development of the rootstocks and enhances plant phosphorus uptake. After root transcriptome sequencing, candidate transcription factor MhMYB15, responsive to Bacillus B2, was identified through heatmap and co-expression network analysis. Yeast one-hybrid, electrophoretic mobility shift assay, and LUC assay confirmed that MhMYB15 can directly bind to the promoter regions of downstream functional genes, including chalcone synthase MhCHS2 and phosphate transporter MhPHT1;15. Transgenic experiments with MhMYB15 revealed that RNAi-MhMYB15 silenced lines failed to induce an increase in flavonoid content and phosphorus levels in the roots under the treatment of Bacillus B2, and plant growth was slower than the control. In conclusion, MhMYB15 actively responds to Bacillus B2, regulating the accumulation of flavonoids and the uptake of phosphorus, thereby influencing plant growth and development.
摘要：
由于土壤中磷的螯合作用，它变得不可用于植物生长和发育。溶磷菌活化固定化磷促进木本植物生长发育的机理,以及内在的分子机制，不清楚。通过分析根际16SV3-V4中的微生物群落和编码磷酸盐有效（PE）和磷酸盐无效苹果砧木中微生物碱性磷酸单酯酶（phoD）的同源基因，发现PE显著富集有益根瘤菌。最好的溶解磷的细菌，Bacillussp.菌株7DB1（B2），被隔离,纯化,并从PE砧木的根际土壤中鉴定。在苹果砧木的根际中与芽孢杆菌B2一起孵育，显着增加了根际土壤中可溶性磷和黄酮的含量。同时,此过程刺激砧木的根系发育并增强植物对磷的吸收。根转录组测序后，通过热图和共表达网络分析鉴定了对芽孢杆菌B2有反应的候选转录因子MhMYB15。酵母单杂种，电泳迁移率变动分析，和LUC实验证实MhMYB15可以直接结合下游功能基因的启动子区域，包括查耳酮合成酶MhCHS2和磷酸盐转运蛋白MhPHT1;15.用MhMYB15进行的转基因实验表明，在芽孢杆菌B2处理下，RNAi-MhMYB15沉默的品系未能诱导根中类黄酮含量和磷水平的增加，并且植物生长比对照慢。总之,MhMYB15主动响应芽孢杆菌B2，调节类黄酮的积累和磷的吸收，从而影响植物的生长发育。
