The phytopathogen Xanthomonas campestris utilizes the divergently transcribed pobA/pobR locus for 4-hydroxybenzoic acid recognition and degradation to promote virulence.

Xanthomonas campestris pv. campestris (Xcc) is the causal agent of black rot in crucifers. Our previous findings revealed that Xcc can degrade 4-hydroxybenzoic acid (4-HBA) via the ß-ketoadipate pathway. This present study expands on this knowledge in several ways. First, we show that infective Xcc cells induce in situ biosynthesis of 4-HBA in host plants, and Xcc can efficiently degrade 4-HBA via the pobA/pobR locus, which encodes a 4-hydroxybenzoate hydroxylase and an AraC-family transcription factor respectively. Next, the transcription of pobA is specifically induced by 4-HBA and is positively regulated by PobR, which is constitutively expressed in Xcc. 4-HBA directly binds to PobR dimers, resulting in activation of pobA expression. Point mutation and subsequent isothermal titration calorimetry and size exclusion chromatography analysis identified nine key conserved residues required for 4-HBA binding and/or dimerization of PobR. Furthermore, overlapping promoters harboring fully overlapping -35 elements were identified between the divergently transcribed pobA and pobR. The 4-HBA/PobR dimer complex specifically binds to a 25-bp site, which encompasses the -35 elements shared by the overlapping promoters. Finally, GUS histochemical staining and subsequent quantitative assay showed that both pobA and pobR genes are transcribed during Xcc infection of Chinese radish, and the strain ΔpobR exhibited compromised virulence in Chinese radish. These findings suggest that the ability of Xcc to survive the 4-HBA stress might be important for its successful colonization of host plants.

[Clinical study on the effect of acupuncture on pregnancy outcome in patients with prethrombotic infertility after repeated implantation failure].

OBJECTIVE: To observe the effect of acupuncture combined with medication on the pregnancy outcome of kidney deficiency and blood stasis type recurrent implantation failure (RIF) in prethrombotic infertility patients. METHODS: A total of 70 RIF patients of kidney deficiency and blood stasis type who were to undergo freeze-thaw embryo transplantation were randomly divided into control and treatment groups, with 35 cases in each group. Patients in the control group were given the basic treatment of artificial periodic freeze-thaw embryo transfer and oral aspirin enteric-coated tablet, 25 mg each time, twice a day, for 3 consecutive menstrual cycles. Patients in the treatment group were treated with acupuncture on the basis of the control group, 30 min each time, 3 times a week, for 3 consecutive menstrual cycles. The clinical pregnancy rate, embryo implantation rate and live birth rate of the two groups were compared. Before treatment and 1 day before transplantation, the scores of kidney deficiency and blood stasis symptom were compared. The blood flow pulse index (PI) and resistance index (RI) of the uterus spiral artery were detected by Doppler ultrasound before treatment and 1 day before transplantation. The endometrial thickness was detected 1 day before transplantation. The contents of plasma D-dimer, serum homocysteine (Hcy) and serum thromboxane B2 (TXB2) were detected. RESULTS: The clinical pregnancy rate, embryo implantation rate and live birth rate in the treatment group were higher than those in the control group (P<0.05). After treatment, the scores of kidney deficiency and blood stasis symptom, the levels of plasma D-dimer, serum Hcy and TXB2, the PI and RI value in both groups were decreased (P<0.05) compared with those before treatment, and the indexes in the treatment group were decreased (P<0.05) more than those in the control group. There was no significant difference in endometrial thickness between the two groups. In the course of treatments, 7 patients in the control group underwent gastric distension pain, poor appetite, constipation, nausea and other gastrointestinal reactions, while only 2 patients in the treatment group had the above discomfort reactions. CONCLUSION: On the basis of medication, acupuncture can reduce the serum TXB2 content in RIF patients in prethrombotic state, improve vascular endothelial function, enhance endometrial tolerance, alleviate the symptoms of kidney deficiency and blood stasis, reduce drug adverse reactions, and ultimately improve the pregnancy outcome and increase the rate of embryo implantation.