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Sugar beets are attacked by several pathogens that cause root damages. Rhizoctonia (Greek for “root killer”) is one of them. Rhizoctonia root rot has become an increasing problem for sugar beet production and to decrease yield losses agronomical measures are adopted. Here, two partially resistant and two susceptible sugar beet genotypes were used for transcriptome analysis to discover new defense genes to this fungal disease, information to be implemented in molecular resistance breeding. Among 217 transcripts with increased expression at 2 days post-infection (dpi), three resistance-like genes were found. These genes were not significantly elevated at 5 dpi, a time point when increased expression of three Bet v I/Major latex protein (MLP) homologous genes BvMLP1, BvMLP2 and BvML3 was observed in the partially resistant genotypes. Quantitative RT-PCR analysis on diseased sugar beet seedlings validated the activity of BvMLP1 and BvMLP3 observed in the transcriptome during challenge by R. solani. The three BvMLP genes were cloned and overexpressed in Arabidopsis thaliana to further dissect their individual contribution. Transgenic plants were also compared to T-DNA mutants of orthologous MLP genes. Plants overexpressing BvMLP1 and BvMLP3 showed significantly less infection whereas additive effects were seen on Atmlp1/Atmlp3 double mutants. The data suggest that BvMLP1 and BvMLP3 may contribute to the reduction of the Rhizoctonia root rot disease in sugar beet. Impact on the defense reaction from other differential expressed genes observed in the study is discussed.

Rhizoctonia solani (Rs) is a soil-borne pathogen with a broad host range. This pathogen incites a wide range of disease symptoms. Knowledge regarding its infection process is fragmented, a typical feature for basidiomycetes. In this study, we aimed at identifying potential fungal effectors and their function. From a group of 11 predicted single gene effectors, a rare lipoprotein A (RsRlpA), from a strain attacking sugar beet was analyzed. The RsRlpA gene was highly induced upon early-stage infection of sugar beet seedlings, and heterologous expression in Cercospora beticola demonstrated involvement in virulence. It was also able to suppress the hypersensitive response (HR) induced by the Avr4/Cf4 complex in transgenic Nicotiana benthamiana plants and functioned as an active protease inhibitor able to suppress Reactive Oxygen Species (ROS) burst. This effector contains a double-psi beta-barrel (DPBB) fold domain, and a conserved serine at position 120 in the DPBB fold domain was found to be crucial for HR suppression. Overall, R. solani seems to be capable of inducing an initial biotrophic stage upon infection, suppressing basal immune responses, followed by a switch to necrotrophic growth. However, regulatory mechanisms between the different lifestyles are still unknown.

31• Phytophthora spp. incite serious plant damages by exploiting a large number of effector 32 proteins and small RNAs (sRNAs). Several reports are describing modulation of host 33RNA biogenesis and defence gene expression. Here, we analysed P. infestans Argonaute 34(Ago) 1 associated small RNAs during potato leaf infection. 35• sRNAs were co-immunoprecipitated, deep sequenced and analysed against the P. 36infestans and potato genomes, followed by transgenic and biochemical analyses on a 37predicted host target. 38• Extensive targeting of potato and pathogen-derived sRNAs to a large number of mRNAs 39 was observed, including 206 sequences coding for resistance (R) proteins in the host 40genome. The single miRNA encoded by P. infestans (miR8788) was found to target a 41 potato lipase-like membrane protein-encoding gene (StLL1) localized to the tonoplast. 42Analyses of stable transgenic potato lines harbouring overexpressed StLL1 or artificial 43 miRNA gene constructs demonstrated the importance of StLL1 during infection by P. 44infestans. Similarly, a miR8788 knock-down strain showed reduced growth on potato 45compared to the wild-type strain 88069. 46• The data suggest that sRNA encoded by P. infestans can affect potato mRNA and thereby 47 promote disease. Knowledge of the impact of pathogen small RNAs in plant defence 48 mechanisms is of major significance to succeed in improved disease control management. 49 50 51

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