*2.2. Isolation of Endophytic Bacterium*

The entophytic bacterium was isolated from healthy onion plants collected from different locations in Hangzhou, China, according to [16] with slight modification. In brief, onion plants were collected at the seedling stage. The plants were washed carefully with tap water to remove the soil, then dried, and classified into leaves and roots. Onion leaves were cut into small pieces (2–3 cm) and disinfected with alcohol (70%) for 1 min followed by sodium hypoxy-chloride (1%) for 5 min and rinsed three times with sterile water under sterile conditions. One gram of sterile tissues was crushed separately in 9 mL saline water (0.85% NaCl), followed by serial dilution up to 10−<sup>5</sup> . For each of these dilutions, 0.1 mL was spread on nutrient agar (NA) medium [8,11,12] bought from Sangon Biotech, Shanghai, and incubated for two days at 30 ◦C. The colonies were purified by transferring single colonies to a new NA plate. The isolated strains were stored in 30% (*v*/*v*) glycerol at −80 ◦C until use.

#### *2.3. Identification of Endophytic Bacterium*

The isolated endophytic bacterium was identified through 16S rRNA gene sequence analysis. The isolate was grown for 24 h in NA medium and a single colony was transferred to NA broth and incubated in a shaker at 30 ◦C overnight. Bacterial DNA was isolated using a genomic bacterial DNA isolation Kit (Sangon Biotech (Shanghai) Co, Ltd., Shanghai, China) following the instructions in the protocol. The 16S rRNA gene was amplified by the bacterial-specific primer pairs 27F (AGAGTTTGATCGCTGCTCAG) and 1492F (GGTTACCTTGTTACGACTT) [17,18]. Complete volumes of PCR amplification in 50 µL were performed using the Bioer XP Thermal Cycler (Hangzhou Bioer Tech. Co., Ltd., Hangzhou, China) in 2× TSINGKE PCR Master Mix (TsingKe Biotechnology, Beijing, China). PCR parameters including the following cycles: the initial denaturation stage was 95 ◦C for 5 min and 30 cycles followed, each of which consisted of denaturation at 94 ◦C for 30 s, annealing at

53 ◦C for 30 s, and extending at 72 ◦C for 1 min. The final extension step was carried out for 5 min at 72 ◦C. PCR amplicons were verified by using Agarose Gel electrophoresis (1%). PCR products were purified by StarPrep Gel Extraction Kit (GeneStar, Beijing, China) and finally submitted for DNA sequencing in TsingKe Biological Technology, Beijing, China. The 16S rRNA gene sequence of the endophytic bacterium was aligned against a reference database using the BLAST server at National Center for Biotechnology Information (NCBI) (http://www.ncbi.nlm.nih.gov). The phylogenetic tree was constructed using the MEGA 6.0 program and the neighbour-joining method [19]. The sequence was deposited in the NCBI database.
