The expression of a rice secondary wall-specific cellulose synthase gene, OsCesA7, is directly regulated by a rice transcription factor, OsMYB58/63
The expression of a rice secondary wall-specific cellulose synthase gene, OsCesA7, is directly regulated by a rice transcription factor, OsMYB58/63
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DOI：
10.1007/s00425-015-2343-z
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发表时间：
2015-09-01
期刊：
影响因子：
4.3
通讯作者：
Umezawa, Toshiaki
中科院分区：
文献类型：
--
作者：
Noda, Soichiro;Koshiba, Taichi;Umezawa, Toshiaki
水稻MYB转录因子OsMYB58/63被发现直接上调水稻次生壁特异的纤维素合成酶基因-纤维素合成酶A7(OsCesA7)的表达；相反，拟南芥可能的同源基因AtMYB58和AtMYB63被证明特异性地激活木质素生物合成。尽管间接证据表明，草本植物在木质纤维生物合成的转录调控方面与双子叶植物相似但部分不同，但对其差异知之甚少。这项研究表明，水稻MYB转录因子OsMYB58/63直接上调了水稻次生壁特异的纤维素合成酶基因--纤维素合成酶A7(OsCesA7)的表达。基因共表达分析表明，在水稻中，OsMYB58/63和几个水稻MYB基因与木质纤维素生物合成酶基因共表达。OsMYB55/61、OsMYB55/61-L、OsMYB58/63和OsMYB42/85在茎节间和节间的表达水平较高。所有四个MYB转录因子都在酵母细胞中作为转录激活剂发挥作用。OsMYB58/63对水稻原生质体中OsCesA7的反式激活作用最强。此外，重组的OsMYB58/63蛋白与OsCesA7启动子中的两个不同的顺式调控元件AC-II和SMRE3结合。这与拟南芥同源基因AtMYB58和AtMYB63的作用形成了鲜明对比，已有报道称AtMYB58和AtMYB63能特异性激活木质素的生物合成。启动子分析表明，作为MYB58和MYB63结合位点的AC元件在拟南芥的纤维素和木聚糖生物合成基因中缺失，而在水稻的纤维素、木聚糖和木质素生物合成基因中存在，这表明水稻和拟南芥转录调控的差异是由于启动子的不同组成。我们的结果为研究禾本科植物木质纤维素生物合成的转录调控提供了新的视角。
A rice MYB transcription factor, OsMYB58/63, was found to directly upregulate the expression of a rice secondary wall-specific cellulose synthase gene, cellulose synthase A7 ( OsCesA7 ); in contrast, the Arabidopsis putative orthologs AtMYB58 and AtMYB63 have been shown to specifically activate lignin biosynthesis.Although indirect evidence has shown that grass plants are similar to but partially different from dicotyledonous ones in transcriptional regulation of lignocellulose biosynthesis, little is known about the differences. This study showed that a rice MYB transcription factor, OsMYB58/63, directly upregulated the expression of a rice secondary wall-specific cellulose synthase gene, cellulose synthase A7 (OsCesA7). Gene co-expression analysis showed that, in rice, OsMYB58/63 and several rice MYB genes were co-expressed with genes encoding lignocellulose biosynthetic enzymes. The expression levels of OsMYB55/61, OsMYB55/61-L, OsMYB58/63, and OsMYB42/85 were commonly found to be high in culm internodes and nodes. All four MYB transcription factors functioned as transcriptional activators in yeast cells. OsMYB58/63 most strongly transactivated the expression of OsCesA7 in rice protoplasts. Moreover, recombinant OsMYB58/63 protein was bound to two distinct cis-regulatory elements, AC-II and SMRE3, in the OsCesA7 promoter. This is in sharp contrast to the role of Arabidopsis orthologs, AtMYB58 and AtMYB63, which had been reported to specifically activate lignin biosynthesis. The promoter analysis revealed that AC elements, which are the binding sites for MYB58 and MYB63, were lacking in cellulose and xylan biosynthetic genes in Arabidopsis, but present in cellulose, xylan, and lignin biosynthetic genes in rice, implying that the difference of transcriptional regulation between rice and Arabidopsis is due to the distinct composition of promoters. Our results provide a new insight into transcriptional regulation in grass lignocellulose biosynthesis.