PsGRASP, a Golgi Reassembly Stacking Protein in Phytophthora sojae, Is Required for Mycelial Growth, Stress Responses, and Plant Infection

The oomycete-specific BAG subfamily maintains protein homeostasis and promotes pathogenicity in an atypical HSP70-independent manner

Protein homeostasis is vital for organisms and requires chaperones like the conserved Bcl-2-associated athanogene (BAG) co-chaperones that bind to the heat shock protein 70 (HSP70) through their C-terminal BAG domain (BD). Here, we show an unconventional BAG subfamily exclusively found in oomycetes. Oomycete BAGs feature an atypical N-terminal BD with a short and oomycete-specific α1 helix (α1'), plus a C-terminal small heat shock protein (sHSP) domain. In oomycete pathogen Phytophthora sojae, both BD-α1' and sHSP domains are required for P. sojae BAG (PsBAG) function in cyst germination, pathogenicity, and unfolded protein response assisting in 26S proteasome-mediated degradation of misfolded proteins. PsBAGs form homo- and heterodimers through their unique BD-α1' to function properly, with no recruitment of HSP70s to form the common BAG-HSP70 complex found in other eukaryotes. Our study highlights an oomycete-exclusive protein homeostasis mechanism mediated by atypical BAGs, which provides a potential target for oomycete disease control.

Genome Mining and Heterologous Expression Guided the Discovery of Antimicrobial Naphthocyclinones from Streptomyces eurocidicus CGMCC 4.1086

A type II polyketide synthase biosynthetic gene cluster (nap) was identified in Streptomyces eurocidicus CGMCC 4.1086 via genome mining. The heterologous expression of the cryptic nap gene cluster in Streptomyces albus J1074 generated dimerized aromatic polyketide naphthocyclinones (1-3), whose structures were determined via extensive analysis using nuclear magnetic resonance and high-resolution electrospray ionization mass spectroscopy. The biological pathway of naphthocyclinone synthesis was revealed via in vivo gene deletion, in vitro biochemical reactions, and comparative genomics. Remarkably, 3 played a crucial role in inhibiting Phytophthora capsici and Phytophthora sojae, with EC₅₀ values of 6.1 and 20.2 μg/mL, respectively. Furthermore, 3 exhibited a potent protective effect against P. capsici and P. sojae in greenhouse tests.

Signal and regulatory mechanisms involved in spore development of Phytophthora and Peronophythora

Oomycetes cause hundreds of destructive plant diseases, threatening agricultural production and food security. These fungus-like eukaryotes show multiple sporulation pattern including the production of sporangium, zoospore, chlamydospore and oospore, which are critical for their survival, dispersal and infection on hosts. Recently, genomic and genetic technologies have greatly promoted the study of molecular mechanism of sporulation in the genus Phytophthora and Peronophythora. In this paper, we characterize the types of asexual and sexual spores and review latest progress of these two genera. We summarize the genes encoding G protein, mitogen-activated protein kinase (MAPK) cascade, transcription factors, RNA-binding protein, autophagy-related proteins and so on, which function in the processes of sporangium production and cleavage, zoospore behaviors and oospore formation. Meanwhile, various molecular, chemical and electrical stimuli in zoospore behaviors are also discussed. Finally, with the molecular mechanism of sporulation in Phytophthora and Peronophythora is gradually being revealed, we propose some thoughts for the further research and provide the alternative strategy for plant protection against phytopathogenic oomycetes.