Gene Expression Modulation of Two Biosynthesis Pathways via Signal Transduction in &amp;lt;i&amp;gt;Cochliobolus heterostrophus&amp;lt;/i&amp;gt;

Ofir Degani

doi:10.4236/abb.2014.54042

Abstract

G-protein-linked pathways have evolved to allow responses to extracellular agonists (hormones, neurotransmitters, odors, chemoattractants, light and nutrients) in eukaryotic cells, ranging from simpler systems, including yeasts, filamentous fungi and slime molds, to more complex organisms, such as mammals. Although the role of G-protein and mitogen-activated protein kinase (MAPK) in filamentous fungi has been studied for over a decade, downstream elements are less known, and the study of target genes has evolved mainly in recent years. Here, we examined the involvement of G-protein subunits and MAPK in controlling the expression of two distinct target genes. These genes were selected from an array database according to their unique expression profile and the role of closely related genes found in other Ascomycetes. One of these genes is BPH, which encodes the enzyme responsible for cytochrome P450-dependent benzoate hydroxylation in microsomes. The other gene is CIPA, which encodes isoflavone reductase (IfR), an enzyme involved in the synthesis of phytoalexin, which catalyzes an intermediate step in pisatin biosynthesis. The expression profile of these two genes was determined in a series of signaling deficiency mutants that were grown on different media using a DNA microarray. Comparison of the expression profile in the two wild type strains and mutants deficient in the G-protein α or β subunits or in MAPK, revealed a unique control mechanism for the BPH and CIPA genes. The two genes are highly expressed during the infection of the host plant leaves and may associate with the fungal response to the host. Signaling via G-protein or MAPK was shown to be related to cascades that altered the expression of these genes in response to the growth condition. This work demonstrates that signal transduction pathways are controlling genes that, although sharing an environmental dependent response, participate in distinct biosynthesis pathways. Moreover, the transcriptional profile may point to distinct and shared roles of the signaling components.

Highlights

The small GTP-binding protein Ras and heterotrimeric G proteins in eukaryotic cells are involved in the transmission of external signals
A mitogen-activated protein kinase (MAPK) module is a known target of Gβγ in budding yeast and mammalian cells [8] [9], and new evidence indicates that some crosstalk may exist between the MAPK and the G-protein pathways in C. heterostrophus as well [5]
The expression of key genes involved in melanin biosynthesis in two C. heterostrophus MAPKs, CHK1 and MPS1, has been shown to be induced significantly under hyperosmotic conditions compared to invariably high expression in the wild type (WT) [13]

Summary

Introduction

The small GTP-binding protein Ras and heterotrimeric G proteins in eukaryotic cells are involved in the transmission of external signals. In Cochliobolus heterostrophus, the agent of Southern Corn Leaf Blight, Gα1 (CGA1) and Gβ (CGB1) subunits, as well as of a mitogen-activated protein kinase (MAPK, CHK1), participates in several developmental pathways Disruption studies of these signaling components results in severe phenotypes, including loss of the normal meandering hyphal growth pattern on hard surfaces, lack of appressorium formation, and defects in mating and virulence [1]-[6]. Both GTP-Gα and free Gβγ can activate downstream targets [7], and an epistatic relationship may exist between the two branches of the G-protein pathway [5]. The expression of key genes involved in melanin biosynthesis in two C. heterostrophus MAPKs, CHK1 and MPS1, has been shown to be induced significantly under hyperosmotic conditions compared to invariably high expression in the wild type (WT) [13]

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Discussion

Conclusion