Cellular messengers involved in the inhibition of the Arabidopsis primary root growth by bacterial quorum-sensing signal N-decanoyl-L-homoserine lactone.

BACKGROUND: N-acyl-homoserine lactones (AHLs) are used as quorum-sensing signals by Gram-negative bacteria, but they can also affect plant growth and disease resistance. N-decanoyl-L-homoserine lactone (C10-HSL) is an AHL that has been shown to inhibit primary root growth in Arabidopsis, but the mechanisms underlying its effects on root architecture are unclear. Here, we investigated the signaling components involved in C10-HSL-mediated inhibition of primary root growth in Arabidopsis, and their interplay, using pharmacological, physiological, and genetic approaches. RESULTS: Treatment with C10-HSL triggered a transient and immediate increase in the concentrations of cytosolic free Ca2+ and reactive oxygen species (ROS), increased the activity of mitogen-activated protein kinase 6 (MPK6), and induced nitric oxide (NO) production in Arabidopsis roots. Inhibitors of Ca2+ channels significantly alleviated the inhibitory effect of C10-HSL on primary root growth and reduced the amounts of ROS and NO generated in response to C10-HSL. Inhibition or scavenging of ROS and NO neutralized the inhibitory effect of C10-HSL on primary root growth. In terms of primary root growth, the respiratory burst oxidase homolog mutants and a NO synthase mutant were less sensitive to C10-HSL than wild type. Activation of MPKs, especially MPK6, was required for C10-HSL to inhibit primary root growth. The mpk6 mutant showed reduced sensitivity of primary root growth to C10-HSL, suggesting that MPK6 plays a key role in the inhibition of primary root growth by C10-HSL. CONCLUSION: Our results indicate that MPK6 acts downstream of ROS and upstream of NO in the response to C10-HSL. Our data also suggest that Ca2+, ROS, MPK6, and NO are all involved in the response to C10-HSL, and may participate in the cascade leading to C10-HSL-inhibited primary root growth in Arabidopsis.

N-3-oxo-hexanoyl-homoserine lactone, a bacterial quorum sensing signal, enhances salt tolerance in Arabidopsis and wheat.

BACKGROUND: N-acyl-homoserine lactones (AHLs) are the quorum sensing (QS) signal molecules to coordinate the collective behavior in a population in Gram-negative bacteria. Recent evidences demonstrate their roles in plant growth and defense responses. RESULTS: In present study, we show that the treatment of plant roots with N-3-oxo-hexanoyl-homoserine lactone (3OC6-HSL), one molecule of AHLs family, resulted in enhanced salt tolerance in Arabidopsis and wheat. We found that the growth inhibition phenotype including root length, shoot length and fresh weight were significantly improved by 3OC6-HSL under salt stress condition. The physiological and biochemical analysis revealed that the contents of chlorophyll and proline were increased and the contents of MDA and Na+ and Na+/K+ ratios were decreased after 3OC6-HSL treatment in Arabidopsis and wheat under salt stress condition. Molecular analysis showed that 3OC6-HSL significantly upregulated the expression of salt-responsive genes including ABA-dependent osmotic stress responsive genes COR15a, RD22, ADH and P5CS1, ABA-independent gene ERD1, and ion-homeostasis regulation genes SOS1, SOS2 and SOS3 in Arabidopsis under salt stress condition. CONCLUSIONS: These results indicated that 3OC6-HSL enhanced plant salt tolerance and ABA-dependent and ABA-independent signal pathways and SOS signaling might be involved in the induction of salt resistance by 3OC6-HSL in plants. Our data provide a new insight into the plant-microbe inter-communication.

[Isolation and identification of Rhodosporidium toruloides R1 degrading N-acyl homoserine lactone].

In the present study, a AHL-utilizing strain RI was isolated and identified as the genus Rhodosporidium toruloides R1 by physi-biochemical approaches and 18S rDNA sequence analysis, and this strain was designated as R. toruloides R1. Results showed that R. toruloides R1 exhibited the ability to utilize and degrade the all N-acyl homoserine lactones tested in this study. Coculture of R. toruloides R1 with Erwinia carotovora subsp. Carotovora effectively inhibit the soft rot disease of patato caused by E. carotovora. To the best of our knowledge, this is the first report on AHL-degradation of yeast cells.

[Construction of recombinant Escherichia coli strains producing poly (4-hydroxybutyric acid) homopolyester from glucose].

The aim of this study is to construct recombinant Escherichia coli strains capable of producing poly(4-hydroxybutyric acid) homopolyester from glucose as sole carbon source. A glutamate: succinate semialdehyde transaminase gene from Escherichia coli, a glutamate decarboxylase gene from E. coli, and a 4-hydroxybutyrate dehydrogenase gene from Ralstonia eutropha were cloned by PCR and assembled onto the plasmid pKSSE5.3 which haboured the PHA synthase gene from Ralstonia eutropha and 4-hydroxybutyrate: CoA transferase from Clostridium kluyveri. The resulting plasmids were transformed into E. coli and the pathway for biosynthesis of poly(4-hydroxybutyric acid) from glucose via alpha-ketoglutarate, an intermediate in TCA cycle was established in recombinant E. coli strains. Recombinant strains synthesized the homopolyester P(4HB), when cells were cultivated in Luria-Bertani broth with glucose as carbon source. P(4HB) accumulation was enhanced up to 30% of cell dry weight, when cells were cultivated in mineral salts M9 medium plus glucose as sole carbon source with addition of yeast extract, tryptone, casein hydrolate into medium respectively.