Molecular Regulation of Arabinan and L-Arabinose Metabolism in Hypocrea jecorina (Trichoderma reesei)
Molecular Regulation of Arabinan and L-Arabinose Metabolism in Hypocrea jecorina (Trichoderma reesei)
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DOI：
10.1128/ec.00162-09
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发表时间：
2009-12-01
期刊：
影响因子：
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通讯作者：
Kubicek, Christian P.
中科院分区：
文献类型：
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作者：
Akel, Eda;Metz, Benjamin;Kubicek, Christian P.
绿僵菌(无性型：里氏木霉)能在植物阿拉伯糖上生长，并能在分泌的阿拉伯聚糖降解酶的帮助下生长。这种在阿拉伯糖及其降解产物L-阿拉伯糖上的生长需要醛糖还原酶XYL1和L-阿拉伯醇脱氢酶LAD1.在缺乏普通纤维素酶和半纤维素酶调节剂XYR1的菌株中，在阿拉伯糖和L-阿拉伯糖上的生长也受到严重影响，但这种损害可以通过编码醛糖还原酶的木糖1的结构性表达来克服。对海藻基因组的研究发现，有四个基因能够降解阿拉伯聚糖，即编码基因abf1、abf2和abf3的α-L-阿拉伯呋喃糖苷酶基因，以及编码具有单独的α-L-阿拉伯呋喃糖苷酶结构域和活性但不编码阿拉伯内切酶的β-木糖苷酶的bxl1基因。转录分析表明，在亲本菌株QM9414中，所有这些基因的表达都受L-阿拉伯糖和L-阿拉伯糖醇的诱导，而在D-葡萄糖上不表达。然而，在缺乏L-阿拉伯糖醇脱氢酶活性的Delta Lad1菌株中，L-阿糖醇的诱导作用显著增强，而在醛糖还原酶(Delta Xyl1)菌株中的诱导作用严重减弱，这表明L-阿拉伯醇与α-L-阿拉伯糖苷酶基因表达之间存在交互作用。带有纤维素酶调节剂xyr1基因敲除的菌株没有表现出任何abf2和bxl1的诱导，并且这种表型不能通过xyl1的结构性表达来逆转。Xyr1功能丧失对abf1和abf3的表达也有轻微影响。我们的结论是，四种α-L-阿拉伯呋喃糖苷酶的表达需要一个早期的途径中间体(L-阿拉伯醇或L-阿拉伯糖)，这是XYL1途径的第一个酶，在ABF2和BXL1的情况下，还需要纤维素酶调节因子XYR1.
Hypocrea jecorina (anamorph: Trichoderma reesei) can grow on plant arabinans by the aid of secreted arabinan-degrading enzymes. This growth on arabinan and its degradation product L-arabinose requires the operation of the aldose reductase XYL1 and the L-arabinitol dehydrogenase LAD1. Growth on arabinan and L-arabinose is also severely affected in a strain deficient in the general cellulase and hemicellulase regulator XYR1, but this impairment can be overcome by constitutive expression of the xyl1 encoding the aldose reductase. An inspection of the genome of H. jecorina reveals four genes capable of degrading arabinan, i.e., the alpha-L-arabinofuranosidase encoding genes abf1, abf2, and abf3 and also bxl1, which encodes a beta-xylosidase with a separate alpha-L-arabinofuranosidase domain and activity but no endo-arabinanase. Transcriptional analysis reveals that in the parent strain QM9414 the expression of all of these genes is induced by L-arabinose and to a lesser extent by L-arabinitol and absent on D-glucose. Induction by L-arabinitol, however, is strongly enhanced in a Delta lad1 strain lacking L-arabinitol dehydrogenase activity and severely impaired in an aldose reductase (Delta xyl1) strain, suggesting a cross talk between L-arabinitol and the aldose reductase XYL1 in an alpha-L-arabinofuranosidase gene expression. Strains bearing a knockout in the cellulase regulator xyr1 do not show any induction of abf2 and bxl1, and this phenotype cannot be reverted by constitutive expression of xyl1. The loss of function of xyr1 has also a slight effect on the expression of abf1 and abf3. We conclude that the expression of the four alpha-L-arabinofuranosidases of H. jecorina for growth on arabinan requires an early pathway intermediate (L-arabinitol or L-arabinose), the first enzyme of the pathway XYL1, and in the case of abf2 and bxl1 also the function of the cellulase regulator XYR1.