| Fusarium wilt,caused by Fusarium oxysporum f.sp.cubense(Foc),is one of the most serious soil-born,vascular disease of banana.It has seriously impacted global banana industry.There is no effective method to control the disease because of the lack of resistance cultivars and poor understanding of the resistance and pathogenicty mechanisms at the molecular level.To understand the molecular mechanism of banana resistance to Foc,we compared infection processes of banana by Foc race 4(Foc4)and Foc race 1(Foc1)using GFP tagged strains and scanning electron microscopy,analyzed banana transcriptome and digital gene expression by sequencing,and carried out comparative proteomic analysis of broths obtained from co-culturing of Foc4 or Foc1 with Cavendish cv.Brazil.Main research results and conclusions were summarized as follows:(1)The infection processes was observed by laser confocal microscopy using GFP-tagged strains of Foc4 and Foc1.Both Foc1 and Foc4 were observed to attach to the root hairs and root epidermis after inoculation,and subsequently invade into the vascular tissues of roots.However,Foc4 was observed to invade the vascular tissues of banana rhizomes while no Foc1 was found in rhizomes two months post-inoculation.Furthermore,it was observed by scanning electron microscopy that Foc4 penetrated into banana roots through the intercellular space of the epidermis and wounds while Foc1 mainly penetrated from the wounds but not from the intercellular space of the epidermis.These results indicated that direct penetrations through the intercellular space and colonization of the rhizome vascular tissues were the key steps in successful Foc4 infection of Cavendish cv.Brazil.(2)Transcriptomic analysis identified at least 842 putative,new banana genes that had not been annotated previously.Digital gene expression analysis was then conducted to assess changes in global gene expression during infections.Gene expression patterns were similar when banana was infected by either Foc1 or Foc4,and both induced expression of many genes commonly responsive to infection by pathogenic microorganisms.These genes include PR genes(such as thaumatin-like genes),genes involved in synthesis of phytoalexins and phenolpropanoids and cell wall strengthening(lignin-forming anionic peroxidase gene).Several genes involved in ethylene biosynthesis and signaling pathways are among genes strongly induced by Foc infections.These genes and pathway were likely involved in banana responses to Foc infections.(3)Changes in Foe pathogens during infection were measured using the iTRAQ quantitative proteomic analysis.Beta-1,3-glucanase,several peroxide enzymes,enzymes involved in energy production and protein synthesis,kinases,stress protein,and killer toxin in Foe were up-regulated after inoculation.Certain peroxide enzymes,and enzymes involved in energy synthesis and protein synthesis were up-regulated in Foc4 but down-regulated or had no obvious changes in Foc1 during their infection to Cavendish cv.Brazil.These data suggest that changes in the expression of these genes might account for the successful infection of by Foc4 but not by Foc1.(4)Changes in banana protein expression during Foe infections were also assessed using the iTRAQ quantitative proteomic analysis.Foc1 and Foc4 infection induced up-regulations of lectins and some peroxide enzymes that related to ROS production in banana.PUB 13 protein involved in the ubiquitin-proteasome pathway was up-regulated only after inoculation by Foc1.Those proteins,especially PUB13,possibly play major roles in the resistance of Cavendish cv.Brazil to Foc1. |
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