Environmental fluctuations such as increased temperature, water availability, and air CO₂ concentration triggered by climate change influence plant disease dynamics by affecting hosts, pathogens, and their interactions. Here, we describe a newly discovered Pseudomonas syringae strain found in a natural population of Arabidopsis thaliana collected from the southwest of France. This strain, called Psy RAYR-BL, is highly virulent on natural Arabidopsis accessions, Arabidopsis model accession Columbia 0, and tobacco plants. Despite the severe disease phenotype caused by the Psy RAYR-BL strain, we identified a reduced repertoire of putative Type III virulence effectors by genomic sequencing compared to P. syringae pv tomato (Pst) DC3000. Furthermore, hopBJ1_Psy is found exclusively on the Psy RAYR-BL genome but not in the Pst DC3000 genome. The plant expression of HopBJ1_Psy induces ROS accumulation and cell death. In addition, HopBJ1_Psy participates as a virulence factor in this plant-pathogen interaction, likely explaining the severity of the disease symptoms. This research describes the characterization of a newly discovered plant pathogen strain and possible virulence mechanisms underlying the infection process shaped by natural and changing environmental conditions.

In Arabidopsis thaliana , the transcription factors WRKY7, WRKY11 and WRKY17 act as negative defence regulators against Pseudomonas syringae pv. tomato (Pst) DC3000. However, their coordinated regulation of gene expression has yet to be fully explored. In this study, we conducted a transcriptomic analysis on the triple mutant wrky7/11/17 in response to Pst DC3000 at 0, 3 and 24 h post‐inoculation (hpi). Our results suggest that at early infection stages (0 and 3 hpi), WRKY7, WRKY11 and WRKY17 significantly repress a group of genes involved in signal perception and transduction, including receptor‐like kinases. Furthermore, at later stages of interaction (24 hpi), these transcription factors induce genes related to the biosynthesis and signalling of the jasmonic acid (JA) pathway. Further infection experiments with Pst DC3000 in plants treated with methyl jasmonate (a JA analogue) and infections with Botrytis cinerea , a pathogen against which JA‐mediated responses are crucial for effective defence, support this proposal. Moreover, we analysed the role of WRKY7, WRKY11 and WRKY17 in alternative splicing regulation. A comparison between differentially expressed (DEG) and spliced (DAS) genes revealed that over 80% of DAS events do not occur in conjunction with overall changes in gene expression. Alternative splicing events were found in genes with functions in splicing and the JA pathway, such as ALY4 , PRP40A , JAZ3 and JAZ10 . These results suggest that WRKY7, WRKY11 and WRKY17 can also participate in this layer of gene expression regulation to modulate immunity negatively.

This chapter will be presented as follow. First, a brief introduction to structure and characterization of lignin and its derivatives is presented, as well as their importance as chemical scaffolds for obtaining value-added products in chemical, food, pharmaceutical and agriculture industry. Second, an extensive review of different reports using computational modeling methods—like molecular dynamics simulations, quantum mechanics and hybrid calculation methods, among others—in the understanding of enzyme-substrate interaction and biocatalysis will be presented. Third, and as last part of chapter, some hand picked examples from literature will be chosen as successful cases where the interplay between experiment and computation has given as a result protein engineered oxidoreductases with improved catalytic capabilities.

The plant cell wall (CW) is a key determinant of plant defense; however, the extent to which natural variation in CW architecture contributes to resistance against phloem-feeding insects remains unclear. Here, we combined genome-wide association studies (GWAS) with functional analyses to identify genetic determinants of resistance against the specialist aphid Brevicoryne brassicae in Arabidopsis thaliana . GWAS conducted on 200 natural accessions identified a single locus on chromosome 2 associated with aphid performance. Integration of haplotype and epidermis-specific expression data prioritized CSLB4 , a member of the cellulose synthase-like B family. Loss-of-function cslb4 mutants showed reduced aphid offspring, indicating enhanced resistance to B. brassicae , whereas performance of the generalist aphid Myzus persicae was unaffected. Electrical penetration graph analyses revealed earlier phloem access on cslb4 mutants despite reduced performance, indicating a decoupling between phloem access and aphid success. Biochemical and immunolocalization analyses showed that CSLB4 disruption altered CW architecture, including increased xyloglucan epitope accessibility in mesophyll cell walls and reduced callose deposition upon aphid infestation. In addition, CSLB4 localized to Golgi-associated compartments, and in silico analyses are consistent with a role in non-cellulosic polysaccharide biosynthesis. Together, these findings identified CSLB4 as a modulator of CW architecture that uncouples phloem access from aphid performance. Highlight: A GWAS identifies CSLB4 as a regulator of cell wall architecture that uncouples aphid-feeding from performance, revealing a new mechanism of plant resistance to specialist insects.