Citrus Huanglongbing,associated with Candidatus Liberibacter asiaticus(Las),is the serious disease of citrus worldwide.Here,we compared differences between leaf and root responses in Wanjincheng Orange(Citrus sinensis...Citrus Huanglongbing,associated with Candidatus Liberibacter asiaticus(Las),is the serious disease of citrus worldwide.Here,we compared differences between leaf and root responses in Wanjincheng Orange(Citrus sinensis Osbeck)to Las infection using leaf-disc grafting.Trees had no obvious symptoms in the first two months after grafting(MAG),but yellowing leaves,thickened midribs and decayed roots began to appear at 6 MAG.The Las growth rate in roots was greater than inmidribs from 2 to 6 MAG;however,by 10 MAG,it was significantly lower in roots than in midribs.Amicroscopic analysis revealed that starch accumulation,callose deposition,cellwall thickness and the number of cell layers increased in the phloem of infected trees.After Las infection,the starch content in the leaves was significantly higher than that in the roots,while the callose deposition in the midribs was 3–19 times that in the roots.A gene expression analysis showed that transcripts of callose-and starch metabolism-related genes were obviously affected by Las infection,and the pathogenesis-related genes PR1,PR2 and PR5 were significantly upregulated and downregulated in midrib and root,respectively.Our results indicated that the PR-mediated resistance response was repressed in root but activated in midrib,which may result in the more rapid Las growth in roots than in midribs during the early infection stage.展开更多
基金supported by grants from the National Key R&D Program of China(Grant No.2018YFD0201500)the Earmarked Fund for the China Agriculture Research System(Grant No.CARS26)the Natural Science Foundation Project of Chongqing(Grant No.cstc2017jcyjBX0020).
文摘Citrus Huanglongbing,associated with Candidatus Liberibacter asiaticus(Las),is the serious disease of citrus worldwide.Here,we compared differences between leaf and root responses in Wanjincheng Orange(Citrus sinensis Osbeck)to Las infection using leaf-disc grafting.Trees had no obvious symptoms in the first two months after grafting(MAG),but yellowing leaves,thickened midribs and decayed roots began to appear at 6 MAG.The Las growth rate in roots was greater than inmidribs from 2 to 6 MAG;however,by 10 MAG,it was significantly lower in roots than in midribs.Amicroscopic analysis revealed that starch accumulation,callose deposition,cellwall thickness and the number of cell layers increased in the phloem of infected trees.After Las infection,the starch content in the leaves was significantly higher than that in the roots,while the callose deposition in the midribs was 3–19 times that in the roots.A gene expression analysis showed that transcripts of callose-and starch metabolism-related genes were obviously affected by Las infection,and the pathogenesis-related genes PR1,PR2 and PR5 were significantly upregulated and downregulated in midrib and root,respectively.Our results indicated that the PR-mediated resistance response was repressed in root but activated in midrib,which may result in the more rapid Las growth in roots than in midribs during the early infection stage.
