Natural variation in Arabidopsis responses toPlasmodiophora brassicaereveals an essential role for RPB1

Abstract

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 no known functional domains or homology to previously characterised proteins. 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 expression in response to infection but this is not sufficient to confer resistance. Constitutive over-expression of RPB1 in Col-0 leads to drastically reduced growth and activation of stress-responsive genes. Furthermore, we found that 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 down-stream of pathogen recognition but required for the elaboration of effective resistance.

New insight into Ca2+‐permeable channel in plant immunity

“…Although our knowledge of Ca 2+ release from the ER in plants is limited compared with that in animals, increasing evidence supports a crucial role for Ca 2+ release from the ER by ER-localized Ca 2+ -permeable channels in regulating Ca 2+ signaling in different aspects of plant biology, particularly plant immunity (He et al, 2021). A recent study identified a resistance gene, WeiTsing (WTS), that encodes an ERlocalized Ca 2+ -permeable channel and confers broadspectrum resistance against Plasmodiophora brassicae in both Arabidopsis and Brassica napus (Ochoa et al, 2023;Wang et al, 2023b). WTS expression is highly induced exclusively in the pericycle upon P. brassicae infection, and WTS subsequently induces the expression of multiple immune-related genes (Wang et al, 2023b).…”