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Abstract Like other eukaryotes, fungi use MAP kinase (MAPK) pathways to mediate cellular changes responding to external stimuli. In the past two decades, three well-conserved MAP kinase pathways have been characterized in various plant pathogenic fungi for regulating responses and adaptations to a variety of biotic and abiotic stresses encountered during plant infection or survival in nature. The invasive growth (IG) pathway is homologous to the yeast pheromone response and filamentation pathways. In plant pathogens, the IG pathway often is essential for pathogenesis by regulating infection-related morphogenesis, such as appressorium formation, penetration, and invasive growth. The cell wall integrity (CWI) pathway also is important for plant infection although the infection processes it regulates vary among fungal pathogens. Besides its universal function in cell wall integrity, it often plays a minor role in responses to oxidative and cell wall stresses. Both the IG and CWI pathways are involved in regulating known virulence factors as well as effector genes during plant infection and mediating defenses against mycoviruses, bacteria, and other fungi. In contrast, the high osmolarity growth (HOG) pathway is dispensable for virulence in some fungi although it is essential for plant infection in others. It regulates osmoregulation in hyphae and is dispensable for appressorium turgor generation. The HOG pathway also plays a major role for responding to oxidative, heat, and other environmental stresses and is overstimulated by phenylpyrrole fungicides. Moreover, these three MAPK pathways crosstalk and coordinately regulate responses to various biotic and abiotic stresses. The IG and CWI pathways, particularly the latter, also are involved in responding to abiotic stresses to various degrees in different fungal pathogens, and the HOG pathway also plays a role in interactions with other microbes or fungi. Furthermore, some infection processes or stress responses are co-regulated by MAPK pathways with cAMP or Ca 2+ /CaM signaling. Overall, functions of individual MAP kinase pathways in pathogenesis and stress responses have been well characterized in a number of fungal pathogens, showing the conserved genetic elements with diverged functions, likely by rewiring transcriptional regulatory networks. In the near future, applications of genomics and proteomics approaches will likely lead to better understanding of crosstalk among the MAPKs and with other signaling pathways as well as roles of MAPKs in defense against other microbes (biotic interactions).
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TatC2 is Important for Growth of Acinetobacter baylyi Under Stress Conditions
Protein export pathways are important for bacterial physiology among pathogens and non-pathogens alike. This includes the Twin-Arginine Translocation (Tat) pathway, which transports fully folded proteins across the bacterial cytoplasmic membrane. Some Tat substrates are virulence factors, while others are important for cellular processes like peptidoglycan remodeling. Some bacteria encode more than one copy of each Tat component, including the Gram-negative soil isolate Acinetobacter baylyi. One of these Tat pathways is essential for growth, while the other is not. We constructed a loss-of-function mutation to disrupt the non-essential tatC2 gene and assessed its contribution to cell growth under different environmental conditions. While the tatC2 mutant grew well under standard laboratory conditions, it displayed a growth defect and an aberrant cellular morphology when subjected to high temperature stress including an aberrant cellular morphology. Furthermore, increased sensitivities to detergent suggested a compromised cell envelope. Lastly, using an in vitro co-culture system, we demonstrate that the non-essential Tat pathway provides a growth advantage. The findings of this study establish the importance of the non-essential Tat pathway for optimal growth of A. baylyi in stressful environmental conditions.
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- Award ID(s):
- 1615822
- PAR ID:
- 10121389
- Date Published:
- Journal Name:
- Fine focus
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2381-0637
- Page Range / eLocation ID:
- 37-50
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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