The TNL gene Rdr1 confers broad‐spectrum resistance to Diplocarpon rosae

Abstract

Black spot disease, which is caused by the ascomycete Diplocarpon rosae, is the most severe disease in field-grown roses in temperate regions and has been distributed worldwide, probably together with commercial cultivars. Here, we present data indicating that muRdr1A is the active Rdr1 gene, a single-dominant TIR-NBS-LRR (Toll/interleukin-1 receptor-nucleotide binding site-leucine rich repeat) (TNL)-type resistance gene against black spot disease, which acts against a broad range of pathogenic isolates independent of the genetic background of the host genotype. Molecular analyses revealed that, compared with the original donor genotype, the multiple integrations that are found in the primary transgenic clone segregate into different integration patterns in its sexual progeny and do not show any sign of overexpression. Rdr1 provides resistance to 13 different single-spore isolates belonging to six different races and broad field mixtures of conidia; thus far, Rdr1 is only overcome by two races. The expression of muRdr1A, the active Rdr1 gene, leads to interaction patterns that are identical in the transgenic clones and the non-transgenic original donor genotype. This finding indicates that the interacting avirulence (Avr) factor on the pathogen side must be widespread among the pathogen populations and may have a central function in the rose-black spot interaction. Therefore, the Rdr1 gene, pyramided with only a few other R genes by sexual crosses, might be useful for breeding roses that are resistant to black spot because the spread of new pathogenic races of the fungus appears to be slow.

Analysis of the Rdr1 gene family in different Rosaceae genomes reveals an origin of an R-gene cluster after the split of Rubeae within the Rosoideae subfamily

“…Previously, we characterized members of the Rdr1 gene family, among which the Rdr1 gene confers resistance to black spot [24,25] and forms a cluster of closely related genes. As no complete genome was available at that time, our analyses were constricted to the region captured by BAC contigs and previous versions of the Fragaria genome (and others).…”

“…In a R. multiflora hybrid (88/124-46), the single dominant TNL gene Rdr1 (muRdr1A), a member of a multigene family of at least nine highly similar clustered TNLs (muRdr1A-muR-dr1I), confers broad-spectrum resistance against black spot [24,25]. The sizes of all TNLs for the Rdr1 locus, except muRdr1D (interrupted by 6957-bp transposable-element insertion within intron), range from 4085 to 5920 bp with sequence similarities between 78.0% and 99.5%.…”

Interaction of roses with a biotrophic and a hemibiotrophic leaf pathogen leads to differences in defense transcriptome activation

“…The control leaves and leaves infected with either D. rosae or P. pannosa were sampled at 0, 24, and 72 hpi for the microscopic analysis. Leaf pieces of approximately 1 cm 2 were fixed, stained with Alexa Fluor 488-conjugated wheat germ agglutinin (Invitrogen, Carlsbad, USA) and examined as previously described (Menz et al 2017).…”

“…Primers for the genes were constructed using Primer3plus (Rozen and Skaletsky 2000) and are listed in Supplementary Table 1. The primer efficiency was tested with a dilution series (1:4, 1:16, 1:64, 1:256) using a StepOnePlus™ system from Applied Biosystems (Austin, USA) as described by Menz et al (2017). The expression of the differentially regulated genes and the three reference genes TIP, SAND and UBC (Klie and Debener 2011) were analyzed using a Fluidigm Dynamic Array IFC (96.96) (Fluidigm Corperation, San Francisco, USA) following the manufacturer's instructions.…”

A draft genome sequence of the rose black spot fungus Diplocarpon rosae reveals a high degree of genome duplication

“…To date up to 11 pathogenic races differentiated on different sets of host plants have been characterized by various authors [ 15 , 16 ] and the interaction of host and pathogen has been studied by histological and biochemical methods [ 14 , 17 , 18 ]. On the host side several studies addressed host resistance and a number of R-genes (resistance genes) were characterized [ 19 , 20 , 21 ], one of which was characterized as a TNL type resistance gene which mediates resistance against different isolates of the pathogen including DortE4 [ 22 , 23 , 24 ]. An interesting aspect of the pathogen biology relates to observations that indicate a low mobility of new genetic variants within and between host populations most probably due to the spread of conidia via splash water [ 25 ].…”