Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Proc Natl Acad Sci U S A. 2013 Aug 13;110(33):13660-5. doi: 10.1073/pnas.1312234110. Epub 2013 Jul 30.
There is considerable debate over the capacity of the cell wall polymer lignin to incorporate unnatural monomer units. We have identified Tnt1 retrotransposon insertion mutants of barrel medic (Medicago truncatula) that show reduced lignin autofluorescence under UV microscopy and red coloration in interfascicular fibers. The phenotype is caused by insertion of retrotransposons into a gene annotated as encoding cinnamyl alcohol dehydrogenase, here designated M. truncatula CAD1. NMR analysis indicated that the lignin is derived almost exclusively from coniferaldehyde and sinapaldehyde and is therefore strikingly different from classical lignins, which are derived mainly from coniferyl and sinapyl alcohols. Despite such a major alteration in lignin structure, the plants appear normal under standard conditions in the greenhouse or growth chamber. However, the plants are dwarfed when grown at 30 °C. Glycome profiling revealed an increased extractability of some xylan and pectin epitopes from the cell walls of the cad1-1 mutant but decreased extractability of others, suggesting that aldehyde-dominant lignin significantly alters cell wall structure.
关于细胞壁聚合物木质素是否能够掺入非天然单体单元，存在相当大的争议。我们已经鉴定出了桶状 medic（Medicago truncatula）的 Tnt1 反转录转座子插入突变体，在 UV 显微镜下，这些突变体的木质素自发荧光减少，间纤维呈现红色。这种表型是由反转录转座子插入一个注释为编码肉桂醇脱氢酶的基因引起的，在这里将其指定为 M. truncatula CAD1。NMR 分析表明，木质素几乎完全来自松柏醛和芥子醛，因此与经典木质素明显不同，经典木质素主要来自松柏醇和芥子醇。尽管木质素结构发生了如此重大的改变，但在温室或生长室的标准条件下，这些植物看起来正常。然而，当在 30°C 下生长时，植物会矮化。糖组分析显示，cad1-1 突变体细胞壁中的一些木聚糖和果胶表位的提取率增加，但其他表位的提取率降低，这表明醛基主导的木质素显著改变了细胞壁结构。
