A Putative D-Arabinono-1,4-lactone Oxidase, MoAlo1, Is Required for Fungal Growth, Conidiogenesis, and Pathogenicity in Magnaporthe oryzae

Magnaporthe oryzae is the causal agent of rice blast outbreaks. L-ascorbic acid (ASC) is a famous antioxidant found in nature. However, while ASC is rare or absent in fungi, a five-carbon analog, D-erythroascorbic acid (EASC), seems to appear to be a substitute for ASC. Although the antioxidant function of ASC has been widely described, the specific properties and physiological functions of EASC remain poorly understood. In this study, we identified a D-arabinono-1,4-lactone oxidase (ALO) domain-containing protein, MoAlo1, and found that MoAlo1 was localized to mitochondria. Disruption of MoALO1 (ΔMoalo1) exhibited defects in vegetative growth as well as conidiogenesis. The ΔMoalo1 mutant was found to be more sensitive to exogenous H2O2. Additionally, the pathogenicity of conidia in the ΔMoalo1 null mutant was reduced deeply in rice, and defective penetration of appressorium-like structures (ALS) formed by the hyphal tips was also observed in the ΔMoalo1 null mutant. When exogenous EASC was added to the conidial suspension, the defective pathogenicity of the ΔMoalo1 mutant was restored. Collectively, MoAlo1 is essential for growth, conidiogenesis, and pathogenicity in M. oryzae.

Hydrogen Peroxide Accumulation Regulated by LjRbohD Modulates Nodulation of Lotus japonicus Under Blue Light

In many legumes, roots that are exposed to blue light do not form nodules, and blue light induces the biosynthesis of hydrogen peroxide (H2O2). The mechanism of blue light restraining nodulation is poorly understood. Whether H2O2 induced by blue light inhibits nodulation needs to be further studied. In this work, blue light could promote the production of H2O2, activate the expression of LjRbohD and LjRbohE, while inhibit the expression of LjRbohB. After applying exogenous H2O2 and diphenyleneiodonium chloride (DPI), the results show H2O2 induced by blue light represses the nodulation of MG20. The accumulated H2O2 may be generated by LjRbohD, which supported by Q-PCR. Cryptochrome 1A, a blue light photoreceptor, is high expression under blue light. However, there seems to be no direct relationship between LjRbohD and LjCry1A. On the contrary, LjRbohB, a positive governor in the regulation of nitrogen fixation activity in L. japonicus, may be negatively regulated by LjCry1A according to the hairy roots transformation results. Therefore, the mechanisms of regulating the nodulation in L. japonicus by LjRbohB and LjRbohD are quite different under blue light. Keywords: Louts japonicus, accumulated H2O2, blue light, nodulation, LjRbohs.