Sphingolipid-induced cell death in Arabidopsis is negatively regulated by the papain-like cysteine protease RD21

It is now well established that sphingoid Long Chain Bases (LCBs) are crucial mediators of programmed cell death. In plants, the mycotoxin fumonisin B1 (FB1) produced by the necrotrophic fungus Fusarium moniliforme disrupts the sphingolipid biosynthesis pathway by inhibiting the ceramide synthase leading to an increase in the amount of phytosphingosine (PHS) and dihydrosphingosine (DHS), the two major LCBs in Arabidopsis thaliana. To date, the signaling pathway involved in FB1-induced cell death remains largely uncharacterized. It is also well acknowledged that plant proteases such as papain-like cysteine protease are largely involved in plant immunity. Here, we show that the papain-like cysteine protease RD21 (responsive-to-desiccation-21) is activated in response to PHS and FB1 in Arabidopsis cultured cells and leaves, respectively. Using two allelic null mutants of RD21, and two different PCD bioassays, we demonstrate that the protein acts as a negative regulator of FB1-induced cell death in Arabidopsis

Molecular analysis of rejection and injury in liver transplant biopsies: The INTERLIVER STUDY

Background. Distinguishing T cell-mediated rejection (TCMR) from other sources of inflammation in liver transplant biopsies by histology has been challenging. Recent progress in molecular assessment of kidney, heart, and lung transplants suggests that microarray biopsy phenotyping would provide novel insights for liver transplantation. Method. We prospectively studied 102 liver transplant biopsies (90% for indications) from USA, Canada, Europe, and Australia with gene expression microarrays (INTERLIVER ClinicalTrials.gov NCT03193151). We used 453 kidney-derived rejection-associated transcripts (RATs) in unsupervised archetypal (AA) and principal component analyses (PCA). Results. Every liver biopsy yielded abundant high quality RNA for microarray analysis. In PCA, principal component 1 correlated with transcripts associated with inflammation (e.g. PTPRC/CD45), TCMR (e.g. Granzyme A) and interferon-gamma effects (e.g. GBP5), and with histologic portal triaditis; PC2 correlated with injury-induced transcripts (e.g. SERPINB8). AA identified 3 archetypes (A1, A2, and A3) and scored every biopsy for similarity to each: S1normal, S2TCMR, and S3injury (Figure 1, with biopsies colored by highest score). Biopsy groups were studied for expression of previously annotated transcript sets (Table 1). S1normal biopsies lacked rejection, inflammation, and injury. S2TCMR biopsies had high expression of rejection- and IFNG-inducible transcripts. S3injury biopsies had increased transcripts reflecting injury and cellular damage (e.g. DAMPs), and were early post-transplant i.e. had donation-implantation injury. Additional 5-archetype analyses suggested a small subclass of late biopsies with plasma cells and mast cell transcripts, which in other organs are associated with fibrosis. No biopsies manifested molecular changes suggesting ABMR. Conclusion. Molecular phenotyping classifies liver transplant biopsies as normal, TCMR, and early injury. The incidence of biopsies with TCMR-like changes (25%) was higher than in other organ transplants which raises the possibility that immunoregulatory mechanisms such as T cell exhaustion may be operating