Elucidating hormone transduction and the protein response of soybean roots to drought stress based on ultra performance liquid chromatography–tandem mass spectrometry and four-dimensional data-independent acquisition

Drought stress can affect the growth and development of soybean, an important cultivated crop. As the main water-absorbing organ, it is particularly important to study the drought response mechanism of roots. Plant hormones are associated with almost all basic biological processes and are used as candidate targets for improving plant stress resistance by regulating cell signal transduction related to stress resistance. In this study, ultra performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) and four-dimensional data-independent (4D-DIA) techniques were used to study the root hormone changes (5%, 10%, 15% and 20% drought stress level) and proteomic responses (15% drought stress level) of different drought-tolerant varieties (drought-resistant HN44 and drought-sensitive HN65) under drought stress. The root activity, CAT activity and soluble sugar content of HN44 were basically higher than those of HN65 under different drought stress levels and days. In the two varieties, some plant hormones, such as abscisic acid (ABA) and salicylic acid (SA), accumulated with an increase in drought degree, and the accumulation of these hormones can give plants a certain degree of drought resistance. Most of the plant hormones peaked at 5–15% drought stress level, and the overall content of jasmonic acid (JA) and cytokinin (CKs) decreased. Differences in the expression of key enzymes involved in hormone signal transduction, such as GH3, TCH4, and PR1, affect a variety of processes and lead to differences in drought resistance between the two varieties. In addition, HN44 had more upregulated proteins in important antioxidant pathways such as glutathione metabolism, phenylpropanoid biosynthesis, and isoflavone biosynthesis. Important drought-responsive proteins, such as PAL, 4CL, and VR, have also been characterized in HN44. In general, the drought-resistant variety was substantially better than the drought-sensitive variety in terms of hormone signaling and antioxidant capacity. These candidate proteins can be used as potential targets for improving drought resistance.