Abstract
Paenibacillus polymyxa (SQR-21) is not only a plant growth-promoting rhizobacteria, but also an effective biocontrol agent against Fusarium wilt disease of watermelon. For the better understanding and clarifying the potential mechanisms of SQR-21 to improve watermelon growth and disease resistance, a split-root methodology in hydroponic and LC–MS technology with the label free method was used to analyze the key root proteins involved in watermelon metabolism and disease resistance after the inoculation of SQR-21. Out of 623 identified proteins, 119 proteins were differentially expressed when treatment (SQR-21 inoculation) and control (no bacterial inoculation) were compared. Among those, 57 and 62 proteins were up-regulated and down-regulated, respectively. These differentially expressed proteins were identified to be involved in signal transduction (ADP-ribosylation factor, phospholipase D), transport (aspartate amino-transferase), carbohydratemetabolic (glucose-6-phosphate dehydrogenase, UDP-glucose pyrophosphorylase), defense and response to stress (glutathione S-transferase, Ubiquitin-activating enzyme E1), and oxidation–reduction process (thioredoxin peroxidase, ascorbate peroxidase). The results of this study indicated that SQR-21 inoculation on the watermelon roots benefits plant by inducing the expression of several proteins involved in growth, photosynthesis, and other metabolic and physiological activities.
Highlights
Plant growth promoting rhizobacteria (PGPR), live freely in the soil and plant rhizosphere, can promote plant growth and mineral nutrition and restrain harmful microbes (Kloepper and Schroth 1978)
The results indicated that strain Paenibacillus polymyxa SQR-21 (SQR-21) colonized the roots of watermelon successfully
We extracted watermelon root proteins and used label free quantitative analysis to investigate the regulation of SQR21 and watermelon interactions
Summary
Plant growth promoting rhizobacteria (PGPR), live freely in the soil and plant rhizosphere, can promote plant growth and mineral nutrition and restrain harmful microbes (Kloepper and Schroth 1978). Researchers showed that P. polymyxa strains effectively colonize the rhizosphere and plant roots and prevent various plant diseases caused by fungi, bacteria, and nematodes (Timmusk et al 2009). P. polymyxa strains help plant absorb nutrients, solubilize phosphorus and produce plant growth regulating hormones (indole-acetic acid, cytokinins, etc.) (Spaepen et al 2007; Lal and Tabacchioni 2009). P. polymyxa secrete phytic acid enzyme which can remove the hexakisphosphate group of inositol to dissolve phosphate. This enzyme can combine the important mineral nutrients (Zn2+, Fe2+ and Ca2+) to eliminate chelate formation of phytic acid salt (Kerovuo et al 1998)
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