The NUP107-160 complex members NUP96/MOS3 and NUP160 are required for defence gene expression in Arabidopsis
by Denise Hartken
Date of Examination:2020-10-07
Date of issue:2021-08-09
Advisor:PD Dr. Marcel Wiermer
Referee:PD Dr. Marcel Wiermer
Referee:Prof. Dr. Volker Lipka
Referee:Prof. Dr. Xin Li
Persistent Address:
http://dx.doi.org/10.53846/goediss-8759
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Abstract
English
Nuclear pore complexes (NPCs) are composed of nucleoporin proteins (NUPs) and are embedded in the double membrane of the nuclear envelope (NE). Arabidopsis NUP96/MOS3 and NUP160 are members of the evolutionary conserved NUP107-160 nuclear pore sub-complex and required for basal resistance and TIR-type NLR protein mediated immunity. Previous data indicated that both NUPs are also involved in the regulation of gene expression. A genome-wide transcriptome analysis was conducted on unchallenged mos3 and nup160 mutant plants using an RNAseq approach to identify new components of MOS3/NUP96- and NUP160-dependent defence responses. This transcriptome analysis revealed mild but significant transcriptional changes of 471 genes that are differentially expressed in both nucleoporin mutants, including the key defence regulator ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and its signalling partner PHYTOALEXIN DEFICIENT4 (PAD4) as well as the pattern recognition receptor EF-Tu RECEPTOR (EFR). Notably, only the expression of a certain set of defence-related genes was affected in mos3 and nup160 plants, suggesting that MOS3 and NUP160 are involved in regulating the expression of specific target genes. The phenotypical consequences of reduced EFR transcript abundance in mos3 and nup160 were investigated in more detail and revealed that both mutants display elevated Agrobacterium-mediated transient transformation efficiency, which is consistent with the function of EFR in restricting plant transformation by Agrobacterium. Reduced EFR gene expression, which is also reflected in reduced EFR protein abundance and impaired EFR-dependent elf18-triggered reactive oxygen species (ROS) production is likely to cause the enhanced transformation events in both mutants. The two genes whose expression was most strongly decreased in the transcriptomes of both mos3 and nup160 mutants are the predicted pumillo family (PUF) RNA binding protein PUM9 (AT1G35730) and the predicted methyl esterase MES18 (AT5G58310), whose functions have not been previously addressed in plant immunity. Using a reverse genetic approach, this study shows that MES18 but not PUM9 is required for basal resistance to the hemi-biotrophic pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. Heterologous expression of MES18 and its subsequent purification and functional characterization showed that MES18 possesses esterase activity towards the methylated, biologically inactive transport forms of the plant hormones indole-3-acetic acid (MeIAA) and jasmonic acid (MeJA). The MES18-mediated hydrolysis of MeIAA to IAA and/or MeJA to JA may therefore be involved in regulating basal resistance to Pst DC3000.
Keywords: NUP107-160 complex; Plant immunity; Plant-Microbe Interaction; Arabidopsis