Baulcombe, D. | Search bioRxiv

bioRxiv2018

Enhanced resistance to bacterial and oomycete pathogens by short tandem target mimic RNAs in tomato

Nucleotide binding site leucine-rich repeat (NLR) proteins of the plant innate immune system are negatively regulated by the miR482/2118 family microRNAs (miRNAs) that are in a distinct 22nt class of miRNAs with a double mode of action. First they cleave the target RNA, as with the canonical 21nt miR-NAs, and second they trigger secondary siRNA production using the target RNA as a template. Here we address the extent to which the miR482/2118 family affects expression of NLR mR-NAs and disease resistance. First we show that structural differences of miR482/2118 family members in tomato (Solanum lycopersicum) are functionally significant. The predicted target of the miR482 subfamily is conserved motif in multiple NLR mRNAs whereas, for miR2118b, it is a novel non-coding RNA target formed by rearrangement of several different NLR genes. From RNA sequencing and degradome data in lines expressing short tandem target mimic (STTM) RNAs of miR482/2118 we confirm the different targets of these miRNAs. The effect on NLR mRNA accumulation is slight but, nevertheless, the tomato STTM lines display enhanced resistance to infection with the oomycete and bacterial pathogens. These data implicate an RNA cascade of miRNAs and secondary siRNAs in the regulation of NLR RNAs and show that the encoded NLR proteins have a role in quantitative disease resistance in addition to dominant gene resistance that has been well characterized elsewhere. We also illustrate the use of STTM RNA in a biotechnological approach for enhancing quantitative disease resistance in highly bred cultivars.

plant biology↗

bioRxiv2017

Frequent paramutation-like features of natural epialleles in tomato

Freakish and rare or the tip of the iceberg? Both phrases have been used to refer to paramutation, an epigenetic drive that contravenes Mendels first law of segregation. Although its underlying mechanisms are beginning to unravel, its understanding relies only on a few examples that may involve transgenes or artificially generated epialleles. By using DNA methylation of introgression lines as an indication of past paramutation, we reveal that the paramutation-like properties of the H06 locus in hybrids of Solanum lycopersicum and a range of tomato relatives and cultivars depend on the timing of sRNA production and conform to an RNA-directed mechanism. In addition, by scanning the methylomes of tomato introgression lines for shared regions of differential methylation that are absent in the S. lycopersicum parent, we identify thousands of candidate regions for paramutation-like behaviour. The methylation patterns for a subset of these regions segregate with non Mendelian ratios, consistent with secondary paramutation-like interactions to variable extents depending on the locus. Together these results demonstrate that paramutation-like epigenetic interactions are common for natural epialleles in tomato, but vary in timing and penetrance.

genomics↗