Differences between appressoria formed by germ tubes and appressorium-like structures developed by hyphal tips in Magnaporthe oryzae.

Abstract

Melanized appressoria are highly specialized infection structures formed by germ tubes of the rice blast fungus Magnaporthe oryzae for plant infection. M. oryzae also forms appressorium-like structures on hyphal tips. Whereas appressorium formation by conidial germ tubes has been well characterized, formation of appressorium-like structures by hyphal tips is under-investigated. In a previous study, we found that the chs7 deletion mutant failed to form appressoria on germ tubes but were normal in the development of appressorium-like structures on artificial hydrophobic surfaces. In this study, we compared the differences between the formation of appressoria by germ tubes and appressorium-like structures by hyphal tips in M. oryzae. Structurally, both appressoria and appressorium-like structures had a melanin layer that was absent in the pore region. In general, the latters were 1.4-fold larger in size but had lower turgor pressure than appressoria, which is consistent with its lower efficiency in plant penetration. Treatments with cAMP, IBMX, or a cutin monomer efficiently induced appressorium formation but not the development of appressorium-like structures. In contrast, coating surfaces with waxes stimulated the formation of both infection structures. Studies with various signaling mutants indicate that Osm1 and Mps1 are dispensable but Pmk1 is essential for both appressorium formation and development of appressorium-like structures on hyphal tips. Interestingly, the cpkA mutant was reduced in the differentiation of appressorium-like structures but not appressorium formation. We also observed that the con7 mutant generated in our lab failed to form appressorium-like structures on hyphal tips but still produced appressoria by germ tubes on hydrophobic surfaces. Con7 is a transcription factor regulating the expression of CHS7. Overall, these results indicate that the development of appressorium-like structures by hyphal tips and formation of appressoria by germ tubes are not identical differentiation processes in M. oryzae and may involve different molecular mechanisms.

• Authors: Ling-An Kong, Guo-Tian Li, Yun Liu, Mei-Gang Liu, Shi-Jie Zhang, Jun Yang, Xiao-Ying Zhou, You-Liang Peng, Jin-Rong Xu
• Journal: Fungal genetics and biology : FG & B (Fungal Genet Biol) Vol. 56 Pg. 33-41 (Jul 2013) ISSN: 1096-0937 [Electronic] United States
• PMID: 23591122 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: Copyright © 2013 Elsevier Inc. All rights reserved.

Chemical References

• Melanins

Topics

• Gene Expression Regulation, Fungal
• Genes, Fungal
• Hyphae (chemistry, cytology)
• Magnaporthe (chemistry, cytology)
• Melanins (analysis)
• Microscopy
• Mutation
• Oryza (microbiology)
• Plant Diseases (microbiology)
• Signal Transduction