Melanin Biosynthesis in the Maize PathogenCochliobolus heterostrophusDepends on Two Mitogen-Activated Protein Kinases, Chk1 and Mps1, and the Transcription Factor Cmr1

Abstract

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.

Alternaria alternata transcription factor CmrA controls melanization and spore development

“…The derived protein Table 2. Oligonucleotides used in this study Eliahu et al, 2007). The alignment of the sequences is shown in Fig.…”

“…heterostrophus and Brm2 in Al. alternata) (Eliahu et al, 2007). The phenolic compound DHN is then probably oxidatively polymerized.…”

“…In Coc. heterostrophus the regulator gene, cmr1 is closely linked to the polyketide synthase and brn1 (Eliahu et al, 2007).…”

Cochliobolus heterostrophus T-toxin gene expression modulation via G protein and MAPK pathways

“…To date, little knowledge exists on downstream signalling elements of these cascades in this species. The influence on target genes expression was demonstrated in only a few instances (Lev & Horwitz 2003;Eliahu et al 2007;Degani et al 2013;Degani 2014a,b).…”

“…Among these are two cellulase genes whose expression is modulated by the MAPK pathway (Degani 2014a;Lev & Horwitz 2003) and four hydrophobins (Degani et al 2013a,b). The expression of key genes involved in melanin biosynthesis in two C. heterostrophus MAPKs, Chk1 and Mps1, has also been shown to be induced significantly under hyperosmotic conditions doi: 10.17221/67/2014-PPS compared to invariably high expression in the wild type (WT) (Eliahu et al 2007).…”