木聚糖在地球上存量豐富,，僅次于纖維素類生物質(zhì)材料,，可作為先進(jìn)生物燃料生產(chǎn)原料。然而,，木聚糖使用中的一個(gè)主要障礙是需要從細(xì)胞壁中提取的難度大,。美國(guó)能源部與聯(lián)合生物能源研究所的研究人員在水稻中找到一種基因,，通過抑制該基因，會(huì)提高木聚糖的提取量和蔗糖合成量,。研究成果已經(jīng)發(fā)表在PNAS,題目是：XAX1 from glycosyltransferase family 61 mediates Xylosyl transfer to rice xylan,。
新發(fā)現(xiàn)的基因稱為XAX1，作用是使木聚糖更易于從細(xì)胞壁中提取,。JBEI的研究人員首先通過基因工程培育突變水稻,，突變株敲掉了XAX1基因，發(fā)現(xiàn)不僅木聚糖更易于從水稻中提取,，產(chǎn)生碳水化合物的糖化反應(yīng)活性提高了60%,。糖化反應(yīng)活性的提高是提高先進(jìn)生物燃料生產(chǎn)生產(chǎn)效率的關(guān)鍵。
木聚糖像纖維素一樣,，是植物細(xì)胞壁的主要組成部分,，也是人類和動(dòng)物營(yíng)養(yǎng)的主要來源。盡管木聚糖非常重要,，但是現(xiàn)在發(fā)現(xiàn)的可以合成多聚糖的酶卻很少,。
研究人員為了找到草本植物中木聚糖合成基因，將研究重點(diǎn)集中在GT61糖基轉(zhuǎn)移酶家族,，過去,，研究人員曾通過生物信息學(xué)方法在一些草類中篩選到GT61酶。水稻是草類研究的模式生物,，研究人員在水稻突變體中插入了14個(gè)基因的片段,，使GT61酶在水稻突變體中高效表達(dá)，突變株命名為XAX1,，因?yàn)橥蛔儗?dǎo)致了XAX1基因被敲出。X1A1基因的作用是在木聚糖鏈上添加特定的木糖等,，使得木聚糖和木質(zhì)素之前的鏈接變得更為復(fù)雜,，增加木聚糖提取的難度。
隨后的分析表明XAX1突變株不能合成阿魏酸,、香豆酸和芳香族化合物等結(jié)合在促進(jìn)木聚糖和木質(zhì)素結(jié)合的阿拉伯糖上的化合物,。另外，突變體還會(huì)有矮化的癥狀,，但研究人員稱已經(jīng)找到一種方法避免矮化,。(生物谷Bioon.com)
doi: 10.1073/pnas.1202079109
PMC:
PMID:
XAX1 from glycosyltransferase family 61 mediates xylosyltransfer to rice xylan
Dawn Chiniquya,b, Vaishali Sharmab, Alex Schultinkc,d, Edward E. Baidoob,e, Carsten Rautengartenb, Kun Chengc,d, Andrew Carrollb, Peter Ulvskovf, Jesper Harholtf, Jay D. Keaslingb,e,g, Markus Paulyc,d, Henrik V. Schellerb,c,e, and Pamela C. Ronalda,b,h,1
Xylan is the second most abundant polysaccharide on Earth and represents an immense quantity of stored energy for biofuel production. Despite its importance, most of the enzymes that synthesize xylan have yet to be identified. Xylans have a backbone of β-1,4–linked xylose residues with substitutions that include α-(1→2)–linked glucuronosyl, 4-O-methyl glucuronosyl, and α-1,2- and α-1,3-arabinofuranosyl residues. The substitutions are structurally diverse and vary by taxonomy, with grass xylan representing a unique composition distinct from dicots and other monocots. To date, no enzyme has yet been identified that is specific to grass xylan synthesis. We identified a xylose-deficient loss-of-function rice mutant in Os02g22380, a putative glycosyltransferase in a grass-specific subfamily of family GT61. We designate the mutant xax1 for xylosyl arabinosyl substitution of xylan 1. Enzymatic fingerprinting of xylan showed the specific absence in the mutant of a peak, which was isolated and determined by 1H-NMR to be (β-1,4-Xyl)4 with a β-Xylp-(1→2)-α-Araf-(1→3). Rice xax1 mutant plants are deficient in ferulic and coumaric acid, aromatic compounds known to be attached to arabinosyl residues in xylan substituted with xylosyl residues. The xax1 mutant plants exhibit an increased extractability of xylan and increased saccharification, probably reflecting a lower degree of diferulic cross-links. Activity assays with microsomes isolated from tobacco plants transiently expressing XAX1 demonstrated xylosyltransferase activity onto endogenous acceptors. Our results provide insight into grass xylan synthesis and how substitutions may be modified for increased saccharification for biofuel generation.
