真菌枯萎病是杨树感染的主要病害之一。质外体是病原菌争夺糖源和宿主识别信号、激活抗逆及免疫的关键场所。研究发现，果糖苷酶抑制蛋白(C/VIFs)定向调控CWIN活性介导糖稳态是质外体防御响应过程的首要因素。如能从此因素入手，运用C/VIFs的调控机制提高杨树的抗病适应性，可为林木病害防治提供有效策略。申请人前期发现两个在根质外体高表达，对枯萎病菌胁迫显著响应和能体外抑制CWIN活性的PtC/VIF家族基因，作为本项目开展的桥梁。为发掘该类基因体内抗逆调控潜能，研究将通过酵母杂交和BiFC等方法鉴定基因体内靶向互作蛋白及病菌胁迫下，上游转录因子和激素的重要调控和拮抗作用；利用双酶法和离子交换色谱等技术分析质外体蔗糖代谢和转运，抗逆基因表达，产物和酶活性等，探索糖免疫和抗逆路径交联现象。通过对比基因沉默和高表达转基因植株的感病表型，揭示该家族基因在杨树根质外体介导调控抗逆防御响应功能和分子机制。

Populus fungal wilt, caused by Fusarium, and seriously affects the survival of the plantation. Pathogenic Fusarium is necrotrophic fungi and hardly to be controlled. Apoplast is a fundamental space for fungi colonization and competition of essential carbon energy with the host. The host may use the apoplast to recognize stress signal, and trigger immune response. The biological process of C/VIFs in the posttranslational regulation of sugar homeostasis in apoplastic space is the primary component of plant defense response; however, its molecular mechanisms and physiological roles are not well documented in Populus. Our previous data showed that two C/VIFs, PtC/VIF1 and PtC/VIF2 were characterized to be highly induced in root as well as in response to Fusarium solani. Functional detection of recombinant of PtC/VIF1 and PtC/VIF2 in vitro suggests their specific inhibition on the activities of CWIN. Examinations of their subcellular localization via transient assay in tobacco epidermis further support that they are targeting to the apoplast. Here, we will initially identify the transcription factors which specifically bind the promoters of PtC/VIF1 and PtC/VIF2 under stress cues. Their inhibitory CWINs and co-expressed genes are explored thereafter. Analyses of transcripts and enzyme activities within sucrose metabolism, transporters, and stress-related genes will help to unravel the cross-talk between defense signaling pathways and sweet immunity pathway. In addition, key environmental factors promoting PtC/VIF1 and PtC/VIF2 expression in response to pathogenic fungi will be identified to link the perturbation and antagonist of fungi colonization. Moreover, phenotypic analyses of the transgenic plants in parallel with wild type will confirm the physiological significance of PtC/VIF1 and PtC/VIF2 in correlation with defense responses. In summary, implement of posttranslational modulation of CWIN in vivo will contribute to orchestrate plant adaptation to biotic stressors via fine-tuning sugar homeostasis. Moreover, our work will provide theoretic basis for improvements of plant stress tolerance and is instrumental for the future molecular breeding.