Identification And Function Of Avr Effector PcAvr1 Of Phytophthora Capsici

Phytophthora capsici belongs to the genus Phytophthora of the order Oomycetes,because in 1922 the first isolated in the host pepper and named.It has been found to host more than one hundred plants in28 families,including pumpkins,cucumbers,peppers and so on.The disease can cause devastating damage to the host.It is a difficult to control,heavy damage to the pathogenic bacteria.Pepper blight parasitic plant way for the typical semi-viviparous nutrient type.In the process of infestation,pepper blast will produce a large number of effectors secreted into the host to overcome the host’s resistance and thus assist the pathogen to infest,of which RxLR(Arg-any amino acid-Leu-Arg)effector is a type that is currently of great interest.The use of plant resistance is an effective means to control P.capsici.Compared with conventional chemical and physical control measures,breeding resistant varieties can better control P.capsici with less environmental impact and greater economic benefits.The process of breeding for disease resistance has been greatly accelerated by exploiting the mechanisms of action of avirulence and resistant genes.Since the first resistance gene was cloned in1992,more than three hundred resistance genes have been cloned in humans.Although significant progress has been made in recent decades in the cloning and identification of oomycete avirulence genes and resistance genes,the research has mainly focused on Phytophthora infestans,Phytophthora sojae and Hyaloperonospora arabidopsidis,which can hardly meet the growing demand in disease resistance breeding.At present,At present,no Avr gene has been cloned on P.capsici,and the accumulation of resistance germplasm resources of P.capsici is still low,and limited resistance resources can be obtained from wild plants,therefore,it is urgent to explore new resistance germplasm resources of P.capsici.Previous studies in the laboratory found that PcAvr1 could induce cell necrosis on Nicotiana benthamiana and Nicotiana tabacum,but the signal pathway of cell necrosis was not clear,and the role of PcAvr1 in the process of Phytophthora capsici infection was still unclear.In order to answer these two scientific questions,four genes,SGT1,HSP90,NDR1 and EDS1,were selected in this paper,and the key gene of PcAvr1 causing cell necrosis was identified by VIGS technology,and the key plant genes of PcAvr1 causing cell necrosis was cleared;the function of PcAvr1 in the process of P.capsici infestation was investigated by inoculating different plant leaves,and it was proved that PcAvr1 is a avirulence gene recognized by the plant of Nicotiana genus and has a dual function,the specific research contents are as follows:1.The cell necrosis induced by the P.capsici effector PcAvr1 is dependent on Nb SGT1 and Nb HSP90We searched for homologs using the DNA and protein sequences of PcAvr1 and found no homologs with more than 50% similarity in other species,suggesting that this effector is unique to P.capsici.We analyzed the available genomic data of P.capsici strain LT263 and found that the gene was significantly expanded to 26 copies,and we named the different copies of the effector as PcAvr1-26 in order of occurrence and cloned them for subsequent experiments.We transiently expressed 26 homologs of PcAvr1 on N.benthamiana and N.tabacum to observe the changes in their ability to cause cell death.The results showed that all copies,except PcAvr1-3/7/16/23,could cause significant cell death in N.benthamiana.All copies except Avr1-7/16 could cause cell death in N.tabacum,indicating that PcAvr1-3 and PcAvr1-23 can cause cell death specific to N.tabacum,which may be related to non-host resistance.Next,we used virus-induced gene silencing(VIGS)technique to silence target genes Nb HSP90,Nb SGT1,Nb NDR1,and Nb EDS1 on N.benthamiana,and transiently expressed PcAvr1-4 and PcAvr1-5on leaves,and showed that silencing Nb NDR1 and Nb EDS1 was able to cause cell death after PcAvr1-4and PcAvr1-5,while silencing Nb HSP90 and Nb SGT1 was not able to cause cell death after PcAvr1-4and PcAvr1-5.These results suggest that cell death induced by PcAvr1 is dependent on Nb HSP90 and Nb SGT1,but not on Nb NDR1 and Nb EDS1.It has been shown that SGT1 is an important component of plant disease resistance genes mediating disease resistance.In contrast,HSP90 is a molecular chaperone that can form a complex with SGT1 in plants and contributes to the stabilization and maturation of NLR proteins,which are required for many disease resistance genes to trigger resistance responses.Combined with the results in this chapter,we hypothesize that PcAvr1 may be a Avr gene with a corresponding disease resistance gene in the genus Tobacco,and that the recognition of this disease resistance gene for PcAvr1-induced cell death is dependent on Nb SGT1 and Nb HSP90.2.P.capsici effector PcAvr1 is an Avr geneWe silenced the effector PcAvr1 in P.capsici and obtained P.capsici PcAvr1 silencing transformants T29 and T35 for inoculation experiments.We inoculated T29 and T35 as well as the wild-type strain LT263 of P.capsici with N.benthamiana,N.tabacum,C.annuum,A.thaliana and C.sativus,respectively.The inoculation results showed that after silencing PcAvr1,P.capsici was able to infect the non-host N.tabacum,with increased pathogenicity to N.benthamiana,no significant change in pathogenicity to C.annuum,and reduced pathogenicity to A.thaliana and C.sativus,indicating that PcAvr1 exercised a avirulence function and was a Avr gene in tobacco plants,while it exercised a virulence function and was a virulence gene in A.thaliana and C.sativus.In summary,our study indicates that PcAvr1 induced cell death on N.benthamiana dependent on Nb SGT1 and Nb HSP90,but not Nb EDS1 and Nb NDR1;and that PcAvr1 is a Avr gene within the Tobacco genus and a virulence gene with a dual role on A.thaliana and C.sativus.