Natural variation in Arabidopsis responses to Plasmodiophora brassicae reveals an essential role for Resistance to Plasmodiophora brasssicae 1 (RPB1).

Despite the identification of clubroot resistance genes in various Brassica crops our understanding of the genetic basis of immunity to Plasmodiophora brassicae infection in the model plant Arabidopsis thaliana remains limited. To address this issue, we performed a screen of 142 natural accessions and identified 11 clubroot-resistant Arabidopsis lines. Genome-wide association analysis identified several genetic loci significantly linked with resistance. Three genes from two of these loci were targeted for deletion by CRISPR/Cas9 mutation in resistant accessions Est-1 and Uod-1. Deletion of Resistance to Plasmodiophora brassicae 1 (RPB1) rendered both lines susceptible to the P. brassicae pathotype P1+. Further analysis of rpb1 knock-out Est-1 and Uod-1 lines showed that the RPB1 protein is required for activation of downstream defence responses, such as the expression of phytoalexin biosynthesis gene CYP71A13. RPB1 has recently been shown to encode a cation channel localised in the endoplasmic reticulum. The clubroot susceptible Arabidopsis accession Col-0 lacks a functional RPB1 gene; when Col-0 is transformed with RPB1 expression driven by its native promoter it is capable of activating RPB1 transcription in response to infection, but this is not sufficient to confer resistance. Transient expression of RPB1 in Nicotiana tabacum induced programmed cell death in leaves. We conclude that RPB1 is a critical component of the defence response to P. brassicae infection in Arabidopsis, acting downstream of pathogen recognition but required for the elaboration of effective resistance.

Identification of mycotoxins by UHPLC-QTOF MS in airborne fungi and fungi isolated from industrial paper and antique documents from the Archive of Bogotá.

Mold deterioration of historical documents in archives and libraries is a frequent and complex phenomenon that may have important economic and cultural consequences. In addition, exposure to toxic fungal metabolites might produce health problems. In this work, samples of broths of fungal species isolated from the documentary material and from indoor environmental samples of the Archive of Bogotá have been analyzed to investigate the presence of mycotoxins. High resolution mass spectrometry made possible to search for a large number of mycotoxins, even without reference standards available at the laboratory. For this purpose, a screening strategy based on ultra-high pressure liquid chromatography coupled to quadrupole-time of flight mass spectrometry (UHPLC-QTOF MS) under MS(E) mode was applied. A customized home-made database containing elemental composition for around 600 mycotoxins was compiled. The presence of the (de)protonated molecule measured at its accurate mass was evaluated in the samples. When a peak was detected, collision induced dissociation fragments and characteristic isotopic ions were also evaluated and used for tentative identification, based on structure compatibility and comparison with literature data (if existing). Up to 44 mycotoxins were tentatively identified by UHPLC-QTOF MS. 34 of these tentative compounds were confirmed by subsequent analysis using a targeted LC-MS/MS method, supporting the strong potential of QTOF MS for identification/elucidation purposes. The presence of mycotoxins in these samples might help to reinforce safety measures for researchers and staff who work on reception, restoration and conservation of archival material, not only at the Archive of Bogotá but worldwide.

Embriogénesis somática y producción de callo embriogénico friable de dos cultivares de yuca (Manihot esculenta Crantz) / Somatic Embryogenesis and friable embryogenic callus production in two cassava cultivars (Manihot esculenta Crantz)

La yuca (Manihot esculenta Crantz) es un cultivo de alta importancia en países tropicales. La transformación genética de yuca ha sido posible desde hace 15 años mediante la producción que callo embriogénico friable (CEF) a partir de embriones somáticos. En el presente trabajo se evalúan la inducción de embriones somáticos usando tres diferentes auxinas sintéticas y la producción de CEF a partir de éstos en los cultivares de yuca SG107-35 y BRA685. Estos cultivares son resistentes a la bacteriosis vascular de yuca cuyo agente causal es Xanthomonas axonopodis pv. manihotis, una de las principales limitantes del cultivo. Los resultados obtenidos muestran que en ambos cultivares la hormona Picloram a una concentración de 12 mg/l fue más eficiente que 2,4-D y Dicamba para producir embriones somáticos. Adicionalmente se consiguió la producción de CEF y la regeneración de plantas mediante embriogénesis somática en el cultivar BRA685. Los resultados del presente trabajo son importantes para evaluar la transformabilidad de distintos cultivares de yuca. Actualmente este número es bastante reducido principalmente porque la producción de CEF es fuertemente influenciada por el genotipo. Por tal razón solo se transforma de manera rutinaria y eficiente en el cultivar 60444. La posibilidad de transformación de distintos cultivares de yuca permitirá explotar la enorme variabilidad del cultivo, invitándonos a aumentar los esfuerzos para mejorar y universalizar los protocolos de transformación de yuca.

The cassava (Manihot esculenta Crantz) crop has a very important role as a food, feed and a raw material in developing countries; therefore it is a priority to develop technologies oriented to the solution of problems and agronomic improvement of the crop. The genetic transformation of cassava was developed 15 years ago by producing friable embryogenic callus (FEC) from somatic embryos as target tissue for transformation. In the present work we evaluated the induction of somatic embryos by using three different synthetic auxins and the production of FEC from both SG107-35 and BRA685 cassava cultivars; both are resistant to cassava bacterial blight caused by Xanthomonas axonopodis pv. manihotis, the most important bacterial disease affecting the crop. Our results showed that in both cultivars gave rise to somatic embryos in media containing Picloram at a concentration of 12 mg/l being more efficient than using 2,4-D or Dicamba. Additionally the cultivar BRA685 produced regenerative FEC giving rise to plants through somatic embryogenesis. However compared to the model cultivar 60444, FEC production was greatly lower. This work shows new efforts to increase the number of transformable cultivars of cassava and take advantage of the enormous genetic variability of the crop.