Abstract
Continuous-cropping leads to obstacles in crop productivity by the accumulation of p-hydroxybenzoic acid (PHBA) and ferulic acid (FA). In this study, a strain CFA of Pseudomonas was shown to have a higher PHBA- and FA-degrading ability in media and soil and the mechanisms underlying this were explored. Optimal conditions for PHBA and FA degradation by CFA were 0.2 g/l of PHBA and FA, 37°C, and pH 6.56. Using transcriptome analysis, complete pathways that converted PHBA and FA to acetyl coenzyme A were proposed in CFA. When CFA was provided with PHBA and FA, we observed upregulation of genes in the pathways and detected intermediate metabolites including vanillin, vanillic acid, and protocatechuic acid. Moreover, 4-hydroxybenzoate 3-monooxygenase and vanillate O-demethylase were rate-limiting enzymes by gene overexpression. Knockouts of small non-coding RNA (sRNA) genes, including sRNA 11, sRNA 14, sRNA 20, and sRNA 60, improved the degradation of PHBA and FA. When applied to cucumber-planted soil supplemented with PHBA and FA, CFA decreased PHBA and FA in soil. Furthermore, a reduction of superoxide radical, hydrogen peroxide, and malondialdehyde in cucumber was observed by activating superoxide dismutase, catalase, glutathione peroxidase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase in seedlings, increasing the reduced glutathione and ascorbate in leaves, and inducing catalase, urease, and phosphatase in the rhizosphere. CFA has potential to mitigate PHBA and FA stresses in cucumber and alleviate continuous-cropping obstacles.
Highlights
Continuous cropping is a common practice in the intensive farming of many countries (Li et al, 2016)
Due to the p-hydroxybenzoic acid (PHBA) and ferulic acid (FA) degradation that might be regulated by rate-limiting enzymes and small non-coding RNA (sRNA) genes, CFA would mitigate PHBA and FA stresses in cucumber by activating antioxidant and soil enzymes (Figure 1)
Coefficient estimates of quadratic polynomial models for CFA (Supplementary Table 3) showed that the initial concentration of the mixture of PHBA and FA, temperature, and pH were variables correlated with the percentages of degraded PHBA and FA
Summary
Continuous cropping is a common practice in the intensive farming of many countries (Li et al, 2016). A study by Wu et al (2019) isolated a PHBA- and FA-degrading strain of Streptomyces and applied it into cucumber-planted soil, where PHBA and FA were added They found that the strain mitigates PHBA and FA stresses in cucumber and has a potential to alleviate the continuous-cropping obstacle of this plant. It was hypothesized that the strain CFA might have the PHBA- and FA-degrading abilities and would decompose the mixture of PHBA and FA in planted soil, thereby having a potential to mitigate this continuous-cropping obstacle of cucumber. Due to the PHBA and FA degradation that might be regulated by rate-limiting enzymes and sRNA genes, CFA would mitigate PHBA and FA stresses in cucumber by activating antioxidant and soil enzymes (Figure 1). The elution profile was: 0.01 min 15% methanol, and 8 min 35% methanol; methanol was increased to 60% over 10 min, held for min, and decreased to 15% over min, held for 20 min
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