Fructan exohydrolases (FEHs) are structurally related to cell wall invertases. While the latter are ubiquitous in higher plants, the role of FEHs in non-fructan species has remained enigmatic. To explore possible roles of FEHs in maize, a full length putative Zm-6-FEH-encoding cDNA was cloned displaying high sequence similarity with cell wall invertases. For functional characterization, Zm-6-FEH protein was expressed in Picha pastoris and in Nicotiana benthamiana leaves. Enzyme activity of recombinant Zm-6-FEH protein showed a strong preference for levan as substrate. Expression profiling in maize seedlings revealed higher transcript amounts in the more mature leaf parts as compared to the growth zone at the base of the leaf, in good correlation with FEH enzyme activities. Subcellular localization analysis indicated Zm-6-FEH location in the apoplast. Noteworthy, incubation of leaf discs with levan and co-incubation with high levan-producing bacteria selectively up-regulated transcript levels of Zm-6-FEH, accompanied by an increase of 6-FEH enzyme activity. In summary, the results indicate that Zm-6-FEH, a novel fructan exohydrolase of a non-fructan species, may have a role in plant defense against levan-producing bacteria.

果胶外水解酶（FEHs）在结构上与细胞壁转化酶有关。尽管后者在高等植物中无处不在，但FEHs在非果聚糖物种中的作用仍然是个谜。为了探索FEHs在玉米中的可能作用，克隆了全长推定的Zm-6-FEH编码cDNA，显示与细胞壁转化酶的高度序列相似性。为了进行功能表征，Zm-6-FEH蛋白在Picha pastoris和Nicotiana benthamiana中表达树叶。重组Zm-6-FEH蛋白的酶活性显示出对levan作为底物的强烈偏好。与叶基部的生长区相比，玉米幼苗中的表达谱显示出在更成熟的叶部中较高的转录物量，与FEH酶活性具有良好的相关性。亚细胞定位分析表明Zm-6-FEH在质外体中的位置。值得注意的是，叶盘与levan一起孵育以及与levan高产细菌的共孵育选择性地上调了Zm-6-FEH的转录水平，同时增加了6-FEH酶的活性。总之，结果表明，Zm-6-FEH是一种非果聚糖物种的新型果聚糖外切水解酶，可能在植物中防御产生左旋细菌的细菌中发挥作用。