Eliahu Noa, Igbaria Aeid, Rose Mark S, Horwitz Benjamin A, Lev Sophie
Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel.
Eukaryot Cell. 2007 Mar;6(3):421-9. doi: 10.1128/EC.00264-06. Epub 2007 Jan 19.
The maize pathogen Cochliobolus heterostrophus requires two mitogen-activated protein kinases (MAPKs), Chk1 and Mps1, to produce normal pigmentation. Young colonies of mps1 and chk1 deletion mutants have a white and autolytic appearance, which was partially rescued by a hyperosmotic environment. We isolated the transcription factor Cmr1, an ortholog of Colletotrichum lagenarium Cmr1 and Magnaporthe grisea Pig1, which regulates melanin biosynthesis in C. heterostrophus. Deletion of CMR1 in C. heterostrophus resulted in mutants that lacked dark pigmentation and acquired an orange-pink color. In cmr1 deletion strains the expression of putative scytalone dehydratase (SCD1) and hydroxynaphthalene reductase (BRN1 and BRN2) genes involved in melanin biosynthesis was undetectable, whereas expression of PKS18, encoding a polyketide synthase, was only moderately reduced. In chk1 and mps1 mutants expression of PKS18, SCD1, BRN1, BRN2, and the transcription factor CMR1 itself was very low in young colonies, slightly up-regulated in aging colonies, and significantly induced in hyperosmotic conditions, compared to invariably high expression in the wild type. These findings indicate that two MAPKs, Chk1 and Mps1, affect Cmr1 at the transcriptional level and this influence is partially overridden in stress conditions including aging culture and hyperosmotic environment. Surprisingly, we found that the CMR1 gene was transcribed in both sense and antisense directions, apparently producing mRNA as well as a long noncoding RNA transcript. Expression of the antisense CMR1 was also Chk1 and Mps1 dependent. Analysis of chromosomal location of the melanin biosynthesis genes in C. heterostrophus resulted in identification of a small gene cluster comprising BRN1, CMR1, and PKS18. Since expression of all three genes depends on Chk1 and Mps1 MAPKs, we suggest their possible epigenetic regulation.
玉米病原菌异旋孢腔菌（Cochliobolus heterostrophus）需要两种丝裂原活化蛋白激酶（MAPK），即Chk1和Mps1，才能产生正常色素沉着。mps1和chk1缺失突变体的年轻菌落呈现白色且自溶的外观，而高渗环境可部分挽救这种情况。我们分离出了转录因子Cmr1，它是葫芦科炭疽菌（Colletotrichum lagenarium）Cmr1和稻瘟病菌（Magnaporthe grisea）Pig1的直系同源物，在异旋孢腔菌中调节黑色素生物合成。异旋孢腔菌中CMR1的缺失导致突变体缺乏深色色素沉着并呈现橙粉色。在cmr1缺失菌株中，参与黑色素生物合成的假定细胞松弛素脱水酶（SCD1）和羟基萘还原酶（BRN1和BRN2）基因的表达无法检测到，而编码聚酮合酶的PKS18的表达仅适度降低。与野生型始终高表达相比，在chk1和mps1突变体中，PKS18、SCD1、BRN1、BRN2以及转录因子CMR1自身在年轻菌落中的表达非常低，在老化菌落中略有上调，在高渗条件下显著诱导。这些发现表明，两种MAPK，即Chk1和Mps1，在转录水平上影响Cmr1，并且这种影响在包括老化培养和高渗环境在内的应激条件下会部分被克服。令人惊讶的是，我们发现CMR1基因以正义和反义方向转录，显然既产生mRNA也产生长链非编码RNA转录本。反义CMR1的表达也依赖于Chk1和Mps1。对异旋孢腔菌中黑色素生物合成基因的染色体定位分析导致鉴定出一个由BRN1、CMR1和PKS18组成的小基因簇。由于所有这三个基因的表达都依赖于Chk1和Mps1 MAPK，我们推测它们可能存在表观遗传调控。
