Ecotype-specific blockage of tasiARF production by two different RNA viruses in Arabidopsis

Arabidopsis thaliana is one of the most studied model organisms of plant biology with hundreds of geographical variants called ecotypes. One might expect that this enormous genetic variety could result in a differential response to pathogens. Indeed, we observed previously that the Bur ecotype develops much more severe symptoms (upward curling leaves and wavy leaf margins) upon infection with two positive strand RNA viruses of different families (turnip vein-clearing virus, TVCV, and turnip mosaic virus, TuMV). To find the genes potentially responsible for the ecotype- specific response, we performed a differential expression analysis of the mRNA and sRNA pools of TVCV and TuMV-infected Bur and Col plants along with the corresponding mock controls. We focused on the genes and sRNAs that showed an induced or reduced expression selectively in the Bur virus samples in both virus series. We found that the two ecotypes respond to the viral infection differently, yet both viruses selectively block the production of the TAS3 derived small RNA specimen called tasiARF only in the virus-infected Bur plants. The tasiARF normally forms a gradient through the adaxial and abaxial part of the leaf (being more abundant in the adaxial part) and post-transcriptionally regulates ARF4, a major leaf polarity determinant in plants. The lack of tasiARF-mediated silencing could lead to an ectopically expressed ARF4 in the adaxial part of the leaf where the misregulation of auxin-dependent signaling would result in an irregular growth of the leaf blade manifesting as upward curling leaf and wavy leaf margin. QTL mapping using Recombinant Inbred Lines (RILs) suggests that the observed symptoms are the result of a multigenic interaction that allows the symptoms to develop only in the Bur ecotype. The particular nature of genetic differences leading to the ecotype-specific symptoms remains obscure and needs further study

Mapping and DNA sequence characterisation of the Ry(sto) locus conferring extreme virus resistance to potato cultivar 'White Lady'

Virus resistance genes carried by wild plant species are valuable resources for plant breeding. The Ry(sto) gene, conferring a broad spectrum of durable resistance, originated from Solanum stoloniferum and was introgressed into several commercial potato cultivars, including 'White Lady', by classical breeding. Ry(sto) was mapped to chromosome XII in potato, and markers used for marker-assisted selection in breeding programmes were identified. Nevertheless, there was no information on the identity of the Ry(sto) gene. To begin to reveal the identification of Ry(sto), fine-scale genetic mapping was performed which, in combination with chromosome walking, narrowed down the locus of the gene to approximately 1 Mb. DNA sequence analysis of the locus identified six full-length NBS-LRR-type (short NLR-type) putative resistance genes. Two of them, designated TMV2 and TMV3, were similar to a TMV resistance gene isolated from tobacco and to Y-1, which co-segregates with Ry(adg), the extreme virus resistance gene originated from Solanum andigena and localised to chromosome XI. Furthermore, TMV2 of 'White Lady' was found to be 95% identical at the genomic sequence level with the recently isolated Ry(sto) gene of the potato cultivar 'Alicja'. In addition to the markers identified earlier, this work generated five tightly linked new markers which can serve potato breeding efforts for extreme virus resistance

Molecular characterization and In Vitro synthesis of infectious RNA of a Turnip vein-clearing virus isolated from Alliaria petiolata in Hungary.

A tobamovirus was isolated from leaves of Alliaria petiolata plants, showing vein-clearing, interveinal chlorosis, and moderate deformation. Host range experiments revealed a high similarity of isolate ApH both to ribgrass mosaic viruses and turnip vein-clearing viruses. The complete nucleotide sequence of the viral genome was determined. The genomic RNA is composed of 6312 nucleotides and contains four open reading frames (ORF). ORF1 is 3324 nt-long and encodes a polypeptide of about 125.3 kDa. The ORF1 encoded putative replication protein contains an Alphavirus-like methyltransferase domain. ORF2 is 4806 nt-long and encodes a polypeptide of about 182 kDa. The ORF2 encoded putative replication protein contains an RNA-dependent RNA polymerase, catalytic domain. ORF3 encodes the putative cell-to-cell movement protein with a molecular weight of 30.1 kDa. ORF4 overlaps with ORF3 and encodes the coat protein with a size of 17.5 kDa. Sequence comparisons revealed that the ApH isolate has the highest similarity to turnip vein-clearing viruses and should be considered an isolate of Turnip vein-clearing virus (TVCV). This is the first report on the occurrence of TVCV in Hungary. In vitro transcripts prepared from the full-length cDNA clone of TVCV-ApH were highly infectious and induced typical symptoms characteristic to the original isolate of the virus. Since infectious clones of TVCV-ApH and crTMV (another isolate of TVCV) markedly differed in respect to recovery phenotype in Arabidopsis thaliana, it is feasible to carry out gene exchange or mutational studies to determine viral factors responsible for the symptom recovery phenotype

Soil drench treatment with ss-aminobutyric Acid increases drought tolerance of potato

The non-protein amino acid beta-aminobutyric acid (BABA) is known to be a priming agent for a more efficient activation of cellular defence responses and a potent inducer of resistance against biotic and abiotic stresses in plants. Nevertheless, most of the studies on priming have been carried out in Arabidopsis. In potato, the effect of BABA was demonstrated only on biotic stress tolerance. We investigated the effect of BABA on the drought tolerance of potato and found that soil drenched with BABA at a final concentration of 0.3 mM improves the drought tolerance of potato. Water loss from the leaves of the primed plants is attenuated and the yield is increased compared to the unprimed drought-stressed plants. The metabolite composition of the tubers of the BABA-treated plants is less affected by drought than the tuber composition of the non-treated plants. Nitric oxide and ROS (reactive oxygen species) production is increased in the BABA-treated roots but not in the leaves. In the leaves of the BABA-treated plants, the expression of the drought-inducible gene StDS2 is delayed, but the expression of ETR1, encoding an ethylene receptor, is maintained for a longer period under the drought conditions than in the leaves of the non-treated, drought-stressed control plants. This result suggests that the ethylene-inducible gene expression remains suppressed in primed plants leading to a longer leaf life and increased tuber yield compared to the non-treated, drought-stressed plants. The priming effect of BABA in potato, however, is transient and reverts to an unprimed state within a few weeks

Principal component analysis of the metabolite composition of tubers of well-watered and drought-stressed plants without (0x BABA) and with BABA treatment (3x, 5x, 7x BABA – see <b>Fig. 4</b> legend for explanation).

<p>The tubers of five plants were analysed in two bulks, with each bulk containing 4-5 tubers. The data used for the PCA are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114297#pone.0114297.s002" target="_blank">S2 Table</a>.</p

Changes in the RWC, soil water content (A) and gene expression (B) in the leaves of BABA-treated and non-treated control plants.

<p>Four-week-old potted plants were soil drenched with water or a solution of BABA at a final concentration of 0.3 mM in the soil. The irrigation was halted, and the soil water content and leaf RWC were assessed by testing three plants in parallel at each time point. The soil water content was determined gravimetrically for a profile from 5 cm to 7 cm deep. One compound leaf per plant was used for the RWC determination. RNA was isolated from three single leaves derived from three plants. The transcript levels were analysed using RT-PCR. The <i>18S RNA</i> gene with a constitutive level of expression was used as the internal control. The plant test was performed three times and similar results were obtained. The data of one representative experiment are shown in the figure. Asterisks depict differences significant at <i>P</i>≤0.01 (<i>t</i>-test) compared to the non-treated, drought-stressed control.</p