Two dsRNA segments, the replicative forms of two ssRNA viruses of SsHV2/SX247 (Sclerotinia sclerotiorum hypovirus 2) and SsDRV/SX247 (Sclerotinia sclerotiorum debilitation-associated RNA virus), were isolated from the hypovirulent strain SX247 of Sclerotinia sclerotiorum. SsDRV/SX247 has the highest similarities (81% aa identity) with the previously reported virus SsDRV/Ep-1PN. The genome of SsHV2/SX247 is 15,219bp in length with a poly-A tail, and it has only one large putative open reading frame (ORF) that encodes a polyprotein containing RNA-dependent RNA polymerase (RdRp) and viral RNA helicase domains. The RdRp domain shares amino acid similarity with that of CHV1 (23%). However, the genome organization of SsHV2/SX247 is significantly different from that of CHV1 on genomic size and ORFs. We conclude that SsDRV/SX247 is a novel strain in species SsDRV of genus Sclerodarnavirus, whereas SsHV2/SX247 is a representative member of new proposed lineage Gammahypovirus in the family Hypoviridae and confers hypovirulence in its host.

Carbon fixation pathway of plants (CFPP) in photosynthesis converts solar energy to biomass, bio-products and biofuel. Intriguingly, a large number of heterotrophic fungi also possess enzymes functionally associated with CFPP, raising the questions about their roles in fungal development and in evolution. Here, we report on the presence of 17 CFPP associated enzymes (ten in Calvin-Benson-Basham reductive pentose phosphate pathway and seven in C4-dicarboxylic acid cycle) in the genome of Sclerotinia sclerotiorum, a heterotrophic phytopathogenic fungus, and only two unique enzymes: ribulose-1, 5-bisphosphate carboxylase-oxygenase (Rubisco) and phosphoribulokinase (PRK) were absent. This data suggested an incomplete CFPP-like pathway (CLP) in fungi. Functional profile analysis demonstrated that the activity of the incomplete CLP was dramatically regulated during different developmental stages of S. sclerotiorum. Subsequent experiments confirmed that many of them were essential to the virulence and/or sclerotial formation. Most of the CLP associated genes are conserved in fungi. Phylogenetic analysis showed that many of them have undergone gene duplication, gene acquisition or loss and functional diversification in evolutionary history. These findings showed an evolutionary links in the carbon fixation processes of autotrophs and heterotrophs and implicated the functions of related genes were in course of continuous change in different organisms in evolution.

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