Combination of transcriptomic, proteomic, and degradomic profiling reveals common and distinct patterns of pathogen-induced cell death in maize.

Regulated cell death (RCD) is crucial for plant development, as well as in decision-making in plant-microbe interactions. Previous studies revealed components of the molecular network controlling RCD, including different proteases. However, the identity, the proteolytic network as well as molecular components involved in the initiation and execution of distinct plant RCD processes, still remain largely elusive. In this study, we analyzed the transcriptome, proteome, and N-terminome of Zea mays leaves treated with the Xanthomonas effector avrRxo1, the mycotoxin Fumonisin B1 (FB1), or the phytohormone salicylic acid (SA) to dissect plant cellular processes related to cell death and plant immunity. We found highly distinct and time-dependent biological processes being activated on transcriptional and proteome levels in response to avrRxo1, FB1, and SA. Correlation analysis of the transcriptome and proteome identified general, as well as trigger-specific markers for cell death in Zea mays. We found that proteases, particularly papain-like cysteine proteases, are specifically regulated during RCD. Collectively, this study characterizes distinct RCD responses in Z. mays and provides a framework for the mechanistic exploration of components involved in the initiation and execution of cell death.

Mixed Linkage ß-1,3/1,4-Glucan Oligosaccharides Induce Defense Responses in Hordeum vulgare and Arabidopsis thaliana.

Plants detect conserved microbe-associated molecular patterns (MAMPs) and modified "self" molecules produced during pathogen infection [danger associated molecular patterns (DAMPs)] with plasma membrane-resident pattern recognition receptors (PRRs). PRR-mediated MAMP and/or DAMP perception activates signal transduction cascades, transcriptional reprogramming and plant immune responses collectively referred to as pattern-triggered immunity (PTI). Potential sources for MAMPs and DAMPs are microbial and plant cell walls, which are complex extracellular matrices composed of different carbohydrates and glycoproteins. Mixed linkage ß-1,3/1,4-glucan (ß-1,3/1,4-MLG) oligosaccharides are abundant components of monocot plant cell walls and are present in symbiotic, pathogenic and apathogenic fungi, oomycetes and bacteria, but have not been detected in the cell walls of dicot plant species so far. Here, we provide evidence that the monocot crop plant H. vulgare and the dicot A. thaliana can perceive ß-1,3/1,4-MLG oligosaccharides and react with prototypical PTI responses. A collection of Arabidopsis innate immunity signaling mutants and >100 Arabidopsis ecotypes showed unaltered responses upon treatment with ß-1,3/1,4-MLG oligosaccharides suggesting the employment of a so far unknown and highly conserved perception machinery. In conclusion, we postulate that ß-1,3/1,4-MLG oligosaccharides have the dual capacity to act as immune-active DAMPs and/or MAMPs in monocot and dicot plant species.

The Vta1 transcriptional regulator is required for microsclerotia melanization in Verticillium dahliae.

Many fungi are able to produce resting structures, which ensure survival and protect them against various stresses in their habitat such as exposure to UV light, temperature variations, drought as well as changing pH and nutrient conditions. Verticillium dahliae is a plant pathogenic fungus that forms melanized resting structures, called microsclerotia, for survival of time periods without a host. These highly stress resistant microsclerotia persist in the soil for many years and are therefore problematic for an effective treatment of the fungus. The Verticillium transcription activator of adhesion 1 (Vta1) was initially identified as one of several transcriptional regulators that rescue adhesion in non-adhesive Saccharomyces cerevisiae cells. Vta2 and Vta3 are required for early steps in plant infection and colonization and additionally control microsclerotia formation. Here, we show that Vta1 function is different, because it is dispensable for root colonization and infection. Vta1 is produced in the fungal cell during microsclerotia development. Analysis of the deletion mutant revealed that the absence of Vta1 allows microsclerotia production, but they are colorless and no more melanized. Vta1 is required for melanin production and activates transcription of melanin biosynthesis genes including the polyketide synthase encoding PKS1 and the laccase LAC1. The primary function of Vta1 in melanin production is important for survival of microsclerotia as resting structures of V. dahliae.

CC-type glutaredoxins recruit the transcriptional co-repressor TOPLESS to TGA-dependent target promoters in Arabidopsis thaliana.

Glutaredoxins (GRXs) are small proteins which bind glutathione to either reduce disulfide bonds or to coordinate iron sulfur clusters. Whereas these well-established functions are associated with ubiquitously occurring GRXs that encode variants of a CPYC or a CGFS motif in the active center, land plants also possess CCxC/S-type GRXs (named ROXYs in Arabidopsis thaliana) for which the biochemical functions are yet unknown. ROXYs and CC-type GRXs from rice and maize physically and genetically interact with bZIP transcription factors of the TGA family to control developmental and stress-associated processes. Here we demonstrate that ROXYs interact with transcriptional co-repressors of the TOPLESS (TPL) family which are related to Tup1 in fungi and Groucho/TLE in animals. In ROXYs, the functionally important conserved A(L/I)W(L/V) motif at the very C terminus mediates the interaction with TPL. A ternary TGA2/ROXY19/TPL complex is formed when all three proteins are co-expressed in yeast. Loss-of-function evidence for the role of TPL in ROXY19-mediated repression was hampered by the redundancy of the five members of the TPL gene family and developmental defects of higher order tpl mutants. As an alternative strategy, we ectopically expressed known TPL-interacting proteins in order to out-compete the amount of available TPL in transiently transformed protoplasts. Indeed, ROXY19-mediated transcriptional repression was strongly alleviated by this approach. Our data suggest a yet unrecognized function of GRXs acting as adapter proteins for the assembly of transcriptional repressor complexes on TGA-regulated target promoters.