Suen Der Fen, Huang Anthony H C
Center for Plant Cell Biology, Department of Botany and Plant Sciences, University of California, Riverside, California 92521, USA.
J Biol Chem. 2007 Jan 5;282(1):625-36. doi: 10.1074/jbc.M608567200. Epub 2006 Oct 24.
Cell wall hydrolases are well documented to be present on pollen, but their roles on the stigma during sexual reproduction have not been previously demonstrated. We explored the function of the tapetum-synthesized xylanase, ZmXYN1, on maize (Zea mays L.) pollen. Transgenic lines (xyl-less) containing little or no xylanase in the pollen coat were generated with use of an antisense construct of the xylanase gene-coding region driven by the XYN1 gene promoter. Xyl-less and wild-type plants had similar vegetative growth. Electron microscopy revealed no appreciable morphological difference in anther cells and pollen between xyl-less lines and the wild type, whereas immunofluorescence microscopy and biochemical analyses indicated an absence of xylanase on xyl-less pollen. Xyl-less pollen germinated as efficiently as wild-type pollen in vitro in a liquid medium but less so on gel media of increasing solidity or on silk, which is indicative of partial impaired water uptake. Once germinated in vitro or on silk, the xyl-less and wild-type pollen tubes elongated at comparable rates. Tubes of germinated xyl-less pollen on silk did not penetrate into the silk as efficiently as tubes of wild-type pollen, and this lower efficiency could be overcome by the addition of xylanase to the silk. For wild-type pollen, coat xylanase activity on oat spelled xylan in vitro and tube penetration into silk were inhibited by xylose but not glucose. The overall findings indicate that maize pollen coat xylanase facilitates pollen tube penetration into silk via enzymatic xylan hydrolysis.
细胞壁水解酶在花粉上的存在已有充分记载，但其在有性生殖过程中在柱头的作用此前尚未得到证实。我们探究了绒毡层合成的木聚糖酶ZmXYN1对玉米（Zea mays L.）花粉的功能。利用由XYN1基因启动子驱动的木聚糖酶基因编码区的反义构建体，培育出花粉壁中木聚糖酶含量很少或没有的转基因品系（xyl-less）。xyl-less品系和野生型植株营养生长相似。电子显微镜观察显示，xyl-less品系和野生型品系的花药细胞和花粉在形态上没有明显差异，而免疫荧光显微镜观察和生化分析表明xyl-less花粉上没有木聚糖酶。xyl-less花粉在体外液体培养基中的萌发效率与野生型花粉相同，但在固体含量增加的凝胶培养基上或在玉米雌蕊丝上的萌发效率较低，这表明其水分吸收部分受损。一旦在体外或玉米雌蕊丝上萌发，xyl-less花粉管和野生型花粉管以相当的速率伸长。在玉米雌蕊丝上萌发的xyl-less花粉管穿透雌蕊丝的效率不如野生型花粉管，添加木聚糖酶到雌蕊丝上可克服这种较低的效率。对于野生型花粉，体外燕麦木聚糖上的花粉壁木聚糖酶活性以及花粉管穿透雌蕊丝的能力受到木糖而非葡萄糖的抑制。总体研究结果表明，玉米花粉壁木聚糖酶通过酶促水解木聚糖促进花粉管穿透雌蕊丝。
