Li Y, Zheng X, Zhu M, Chen M, Zhang S, He F, Chen X, Lv J, Pei M, Zhang Y, Zhang Y, Wang W, Zhang J, Wang M, Wang Z, Li G, Lu G.

Front Microbiol. 2019 Mar 14;10:444. doi: 10.3389/fmicb.2019.00444. eCollection 2019.

Abstract

Isovaleryl-CoA dehydrogenase (IVD), a member of the acyl-CoA dehydrogenase (ACAD) family, is a key enzyme catalyzing the conversion of isovaleryl-CoA to β-methylcrotonyl-CoA in the third reaction of the leucine catabolism pathway and simultaneously transfers electrons to the electron-transferring flavoprotein (ETF) for ATP synthesis. We previously identified the ETF ortholog in rice blast fungus Magnaporthe oryzae (MoETF) and showed that MoETF was essential for fungal growth, conidiation and pathogenicity. To further investigate the biological function of electron-transferring proteins and clarify the role of leucine catabolism in growth and pathogenesis, we characterized MoIVD (M. oryzae isovaleryl-CoA dehydrogenase). MoIvd is highly conserved in fungi and its expression was highly induced by leucine. The Δmoivd mutants showed reduced growth, decreased conidiation and compromised pathogenicity, while the conidial germination and appressorial formation appeared normal. Consistent with a block in leucine degradation, the Δmoivd mutants accumulated isovaleric acid, grew more slowly, fully lacked pigmentation and completely failed to produce conidia on leucine-rich medium. These defects were largely rescued by raising the extracellular pH, suggesting that the accumulation of isovaleric acid contributes to the growth and conidiation defects. However, the reduced virulence of the mutants was probably due to their inability to overcome oxidative stress, since a large amount of ROS (reactive oxygen species) accumulated in infected host cell. In addition, MoIvd is localized to mitochondria and interacted with its electron receptor MoEtfb, the β subunit of MoEtf. Taken together, our results suggest that MoIVD functions in leucine catabolism and is required for the vegetative growth, conidiation and full virulence of M. oryzae, providing the first evidence for IVD-mediated leucine catabolism in the development and pathogenesis of plant fungal pathogens.

See https://www.ncbi.nlm.nih.gov/pubmed/30923517

Figure 1: Domain structure of MoIvd and phylogenetic analysis of IVD homologs. (A) MoIvd domain prediction by the PFAM website (http://pfam.xfam.org/). The ACAD domain located between aa91 and aa464. The bar indicates 50 amino acids. (B) IVD phylogenetic tree constructed using the observed divergency method by DNAMAN6.0. The IVD protein sequences of 15 model species were collected from NCBI database. The bar indicates 0.05 distance units. The percentage in brackets indicates sequence identity between MoIvd and corresponding homolog. The sequence accession numbers are listed as follows: Magnaporthe oryzae (XP_003721261.1), Arabidopsis thaliana (NP_190116.1), Oryza sativa (XP_015639342.1), Caenorhabditis elegans (NP_500720.1), Danio rerio (NP_958899.1), Homo sapiens (NP_002216.2), Mus musculus (NP_062800.1), Sclerotinia sclerotiorum (APA11203.1), Colletotrichum tofieldiae (KZL76390.1), Trichoderma parareesei (OTA08745.1), Chaetomium thermophilum (XP_006691847.1), Thielavia terrestris (XP_003651516.1), Neurospora crassa (XP_964284.1), Gaeumannomyces tritici (XP_009227932.1) and Escherichia coli (WP_001189854.1).