Identification of genes involved in regulating MnSOD2 production and root colonization in Bacillus cereus 905

sodA2-encoding manganese-containing superoxide dismutase(MnSOD2)in Bacillus cereus 905 plays an essential role in antioxidative stress,nutrition utilization,rhizosphere and phyllosphere colonization.However,the genes involved in regulating the sod A2 expression have not been clearly elucidated in B.cereus.In this study,a genome-wide random insertion mutagenesis was constructed by using transposon TnYLB-1 to identify novel genes regulating the sodA2 expression.Seven mutants that changed the sodA2 expression at both m RNA and protein levels were finally obtained.Sequence analysis and BLAST data showed that the genes disrupted by TnYLB-1 in B.cereus 905 shared high conservations with those in the B.cereus type strain,ATCC 14579.These genes encode heat-inducible transcription repressor,chloride channel protein,recombinase A,ferrous iron transport protein,nucleoside diphosphate kinase,and histidine ammonia-lyase.Besides,we also provided the evidence that the genes regulating the sodA2 expression could influence colonization ability of B.cereus 905 on wheat roots.Specifically,those genes downregulating the sodA2 expression significantly reduced bacterial colonization on wheat roots,and mutants with increased MnSOD2 activities could enhance bacterial population densities on wheat roots to a certain degree.Our work provided information that multiple genes are involved in MnSOD2 production and wheat root colonization.The molecular regulatory pathways through which these genes modulate the sod A2 expression and root colonization need to be investigated extensively in the future.

Function and molecular mechanism analysis of CaLasSDE460 effector involved in the pathogenesis of“Candidatus Liberibacter asiaticus”in citrus

Citrus Huanglongbing(HLB),caused by Candidatus Liberibacter asiaticus(CaLas),is the most serious disease worldwide.CaLasSDE460 was previously characterized as a potential virulence factor of CaLas.However,the function and mechanism of CaLasSDE460 involved in CaLas against citrus is still elusive.Here,we showed that transgenic expression of CaLasSDE460 in Wanjincheng oranges(C.sinensis Osbeck)contributed to the early growth of CaLas and the development of symptoms.When the temperature increased from 25℃to 32℃,CaLas growth and symptom development in transgenic plants were slower than those in WT controls.RNA-seq analysis of transgenic plants showed that CaLasSDE460 affected multiple biological processes.At 25℃,transcription activities of the“Protein processing in endoplasmic reticulum”and“Cyanoamino acid metabolism”pathways increased while transcription activities of many pathways decreased at 32℃.124 and 53 genes,separately annotated to plant-pathogen interaction and MAPK signaling pathways,showed decreased expression at 32℃,compared with these(38 for plant-pathogen interaction and 17 for MAPK signaling)at 25℃.Several important genes(MAPKKK14,HSP70b,NCED3 and WRKY33),remarkably affected by CaLasSDE460,were identified.Totally,our data suggested that CaLasSDE460 participated in the pathogenesis of CaLas through interfering transcription activities of citrus defense response and this interfering was temperature-dependent.