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The ability of plant growth-promoting rhizobacteria (PGPR) to alleviate iron deficiency-induced chlorosis in plants has been widely reported, but the role of siderophores in the re-greening process has rarely been investigated. In this study, the Priestia megaterium ZS-3 (ZS-3) siderophore was first characterized, and a 100-fold concentration of the crude extract of the siderophore was extracted by solid-phase extraction and used to inoculate Arabidopsis thaliana to investigate whether the ZS-3 siderophore could alleviate plant iron deficiency-induced chlorosis in the presence of an insoluble iron source and to determine how it promoted plant growth. The results indicated that -Fe + Fe2O3 (Fe2O3) treatment induced a decrease in plant growth and iron nutritional status compared with those in the 1/2 MS (one-half-strength Murashige and Skoog medium). Expression levels of representative genes for chlorophyll synthesis, CHLM and CHLG, increased by 85.41% and 77.05% compared to Fe2O3 treatment; the IRT1 and FRO2 in Fe2O3 inoculated with the ZS-3 siderophore (T2 treatment) were upregulated by 88.1% and 87.20%, respectively. These results indicate that the ZS-3 siderophore upregulates the expressions of chlorophyll genes to increases photosynthesis and helps plants increase the transcription of iron and the activity of ferric-chelate reductase. Compared with the Fe2O3 treatment, the T2 group increased the soluble protein and chlorophyll contents by 2.64- and 3.47-fold, and improved the activities of ferric-chelate reductase and peroxidase (POD) by 3.69- and 2.9-fold, respectively, indicating that the ZS-3 siderophore maintained normal plant growth under Fe2O3 stress by increasing the activity of antioxidant enzymes. This study revealed that the ZS-3 siderophore Ferrioxamine E M + Fe-2 H enhances plant iron uptake and transport activity at the transcriptional level, confirming the important role of the ZS-3 siderophore in plant iron deficiency status, and the results suggest that the ZS-3 siderophore helps plants acquire iron, alleviates plant chlorosis and promotes plant growth through mechanism I of plant iron acquisition. In this study, we closely linked the structural characterization and quantification of siderophores with Fe deficiency-induced chlorosis to elucidate the promotional mechanism of siderophores in Fe-deficient environments.
Zhu et al. (Wed,) studied this question.