Li L, Cheng X F, Leshkevich J, Umezawa T, Harding S A, Chiang V L
Plant Biotechnology Research Center, School of Forestry, Michigan Technological University, Houghton, MI 49931, USA.
Plant Cell. 2001 Jul;13(7):1567-86. doi: 10.1105/tpc.010111.
Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) has been thought to mediate the reduction of both coniferaldehyde and sinapaldehyde into guaiacyl and syringyl monolignols in angiosperms. Here, we report the isolation of a novel aspen gene (PtSAD) encoding sinapyl alcohol dehydrogenase (SAD), which is phylogenetically distinct from aspen CAD (PtCAD). Liquid chromatography-mass spectrometry-based enzyme functional analysis and substrate level-controlled enzyme kinetics consistently demonstrated that PtSAD is sinapaldehyde specific and that PtCAD is coniferaldehyde specific. The enzymatic efficiency of PtSAD for sinapaldehyde was approximately 60 times greater than that of PtCAD. These data suggest that in addition to CAD, discrete SAD function is essential to the biosynthesis of syringyl monolignol in angiosperms. In aspen stem primary tissues, PtCAD was immunolocalized exclusively to xylem elements in which only guaiacyl lignin was deposited, whereas PtSAD was abundant in syringyl lignin-enriched phloem fiber cells. In the developing secondary stem xylem, PtCAD was most conspicuous in guaiacyl lignin-enriched vessels, but PtSAD was nearly absent from these elements and was conspicuous in fiber cells. In the context of additional protein immunolocalization and lignin histochemistry, these results suggest that the distinct CAD and SAD functions are linked spatiotemporally to the differential biosynthesis of guaiacyl and syringyl lignins in different cell types. SAD is required for the biosynthesis of syringyl lignin in angiosperms.
肉桂醇脱氢酶（CAD；EC 1.1.1.195）被认为在被子植物中介导松柏醛和芥子醛还原为愈创木基和紫丁香基单木质醇。在此，我们报道了一个新的杨树基因（PtSAD）的分离，该基因编码芥子醇脱氢酶（SAD），在系统发育上与杨树CAD（PtCAD）不同。基于液相色谱 - 质谱的酶功能分析和底物水平控制的酶动力学一致表明，PtSAD对芥子醛具有特异性，而PtCAD对松柏醛具有特异性。PtSAD对芥子醛的酶促效率比PtCAD高约60倍。这些数据表明，除了CAD之外，离散的SAD功能对于被子植物中紫丁香基单木质醇的生物合成至关重要。在杨树茎的初生组织中，PtCAD仅免疫定位到沉积有愈创木基木质素的木质部细胞，而PtSAD在富含紫丁香基木质素的韧皮部纤维细胞中大量存在。在发育中的次生茎木质部中，PtCAD在富含愈创木基木质素的导管中最为明显，但在这些细胞中几乎没有PtSAD，而在纤维细胞中则很明显。结合额外的蛋白质免疫定位和木质素组织化学，这些结果表明，不同的CAD和SAD功能在时空上与不同细胞类型中愈创木基和紫丁香基木质素的差异生物合成相关。SAD是被子植物中紫丁香基木质素生物合成所必需的。
