Functional Analysis Of ABR1 In Copper Ions Mediated Potato Res Istance To Late Blight

As the most important disease of the world crops,Potato late blight caused by Phytophthora infestans has made devastating damage in potato production.Cultivating late blight resistant varieties has become one of the main goals of potato breeding.As the representative of copper preparation,Bordeaux liquid is the first commercial broad-spectrum fungicide used to prevent and control potato late blight and other diseases,and has been used for more than one hundred years.Our previous research has found that copper ions can induce ethylene quick burst in potato,of which St EIN3 act as a key factor to interact with ABA1 and NCED1 in the aim of antagonizing abscisic acid synthesis.Also,copper ions have the ability to enhance potatoes resistance caused by Phytophthora infestans which is inhibited by abscisic acid.In addition,previous studies have also found that copper ions can still stimulate potato resistance to late blight in ABA1 over-expressing transplants,suggesting that copper ions may exist other pathways to inhibit ABA signaling.In this study,we analyzed the RNA-seq data in both Arabidopsis thaliana and potatoes treated with copper ions and found that the abscisic acid repressor ABR1（ABA repressor 1）was significantly induced by copper ions.（1）In order to explored the role of ABR1 in copper ions-mediated disease resistance,we confirmed the positive role of Cu²⁺on regulating StABR1 and AtABR1 by quantitative reverse transcription PCR.While restrain the expression of StABR1 by the way of Virus mediated Gene Silencing（Virus get-Induced Gene Silencing,VIGS）not only caused potato become more sensitive to Phytophthora infestans,but also no longer response to copper ions.In addition,abr1 mutant plants of Arabidopsis thaliana which treated with copper ions would no longer induce resistance to Pseudomonas syringae pathovar tomato（Pst）strain,DC3000（Pst DC3000）.All above indicate that ABR1 plays an indispensable role in the disease resistance mediated by copper ions.（2）To identify the mechanisms underlying copper ion-induced ABR1 expression,we used the GFP reporter gene to analyze the different deleted promoters of ABR1,and that transient expressed in Nicotiana benthamiana（NB）.Our result showed that copper ions could promote the expression of ABR1 promoters,bioinformatics predicted that there exist an cis-element GTAC which implied that this cis-element may control copper-induced ABR1expression.Then we constructed GTAC-35S mini and the 35S mini to drive the luc reporter gene,the results showed that copper ions could induce a luc signal in NB leaves transiently expressing GTAC-35S mini:luc.It has been known that SPL transcription factor can specifically bind to GTAC elements,and RNA-seq results show that StSPL8 is induced by copper ions.Transient express 35S promoter-drived StSPL8 in potato could enhance the resistance to late blight.These results indicated that copper ions bind to the promoter of ABR1by activating SPL8 to promote the expression of ABR1,thus improving the disease resistance of potatoes.（3）In order to confirm the resistance signal pathway mediated by ABR1,we prepared ABR1 over expression transgenic potato materials.Compared with wild type,the lesion area and bacteriostasis on potato leaves caused by late blight fungus was significantly reduced in ABR1 over expression transgenic plants and the accumulation of hydrogen peroxide was increased in ABR1 over expression transgenic plants,suggested that over expression ABR1could significantly increase resistance faced with potato late blight.