Maize kernels were sown in soil and grown in a growth chamber (14 h/10 h of light/dark, 30°C/25°C of day/night, 40%/60% relative humidity of day/night, 1,000 lx of light intensity), and the seedlings were grown to the 3-leaf stage for the follow-up experiments.
For determination of phytohormone content, the method was as follows:1) Metabolite extraction: The extraction of JA and asmonoyl-isoleucinewas (JA-Ile) followed the method descripted by Pan et al [55] . 2) Quantitative analysis of JA and JA-Ile . The contents of plant hormones in the samples are determined by Ultra High Performance Liquid Chromatography -Mass Spectrometry (HPLC-MS). The sample were separated by Agilent 1290 Infinity LC ultra-high performance liquid chromatography system. Samples were loaded in an automatic injector at 4 , the liquid chromatography column temperature was 45 . The mobile phase A was 0.05% formic acid aqueous solution, the mobile phase B was 0.05% formic acid acetonitrile solution. The flow rate was 400 μL/min, the sample size was 4μL. The relevant liquid phase gradient was as follows: 0-1min, the B phase changes linearly from 2% to 10%; 1-10min, the B phase changes linearly from 10% to 70%; From 10-11min, the B phase changed linearly from 70% to 95%. From 11-11.1min, the B phase changed linearly from 95% to 2%. From 11.1-13min, the B-phase was maintained at 2%. A QC sample was set up every certain number of experimental samples in the sample queue to detect and evaluate the stability and repeatability of the system. For correction of chromatographic retention time, standard mixtures of target substances was set up in the sample cohort. MS was performed in positive/negative ion mode on a 5500 QTRAP mass spectrometer (SCIEX). 5500 QTRAP ESI source positive ion
For determination of phytohormone content, the method was as follows:1) Metabolite extraction: The extraction of JA and asmonoyl-isoleucinewas (JA-Ile) followed the method descripted by Pan et al [55] . 2) Quantitative analysis of JA and JA-Ile . The contents of plant hormones in the samples are determined by Ultra High Performance Liquid Chromatography -Mass Spectrometry (HPLC-MS). The sample were separated by Agilent 1290 Infinity LC ultra-high performance liquid chromatography system. Samples were loaded in an automatic injector at 4 , the liquid chromatography column temperature was 45 . The mobile phase A was 0.05% formic acid aqueous solution, the mobile phase B was 0.05% formic acid acetonitrile solution. The flow rate was 400 μL/min, the sample size was 4μL. The relevant liquid phase gradient was as follows: 0-1min, the B phase changes linearly from 2% to 10%; 1-10min, the B phase changes linearly from 10% to 70%; From 10-11min, the B phase changed linearly from 70% to 95%. From 11-11.1min, the B phase changed linearly from 95% to 2%. From 11.1-13min, the B-phase was maintained at 2%. A QC sample was set up every certain number of experimental samples in the sample queue to detect and evaluate the stability and repeatability of the system. For correction of chromatographic retention time, standard mixtures of target substances was set up in the sample cohort. MS was performed in positive/negative ion mode on a 5500 QTRAP mass spectrometer (SCIEX). 5500 QTRAP ESI source positive ion
