Phospholipase-ähnliche Proteine bei der Pathogenabwehr von Pflanzen

• Phospholipase-like proteins in plant defense against pathogens

Jansen, Irina; Conrath, Uwe (Thesis advisor); Panstruga, Ralph (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Plants rely on functional defense mechanisms to fend off microbial pathogens. Subsequent to pathogen recognition, cascades that are hierarchically formed of mitogen-activated protein kinases - shortly MPKs - are involved in transduction of the signal of recognition. However, MPK substrates are currently not yet well studied in plants. In transgenic Arabidopsis thaliana that are expressing a constitutively active MPK kinase from tobacco under control of a dexamethasone-inducible promoter phosphopeptides of phospholipase-like PEARLI4 family proteins - refered to as P4L - were identified as substrate candidates of defense-related MPK3 and MPK6 after induction by dexamethasone, with phosphopeptides of P4L1 accumulating to the highest extent. Phosphorylation by MPK6, but not by MPK3 was demonstrated in vitro for both, P4L1 as well as the early Arabidopsis aluminium-induced protein PEARLI4. In comparison to A. thaliana wildtype no changes in susceptibility to the bacterial pa-thogen Pseudomonas syringae pv. maculicola were observed for T-DNA insertion lines in P4L1 to P4L6 as well as PEARLI4. However, after induction of systemic acquired resistance by infection with P. syringae pv. maculicola a challenge infection lead to reduced systemic acquired resistance in T-DNA insertion lines in PEARLI4, P4L2, P4L4 and P4L5. P4L2 / PEARLI4 and P4L4 / P4L5 are adjacent on chromosome 2 or 4 respectively. Thus, a gene duplication event might have occurred ultimately leading to four proteins with possibly redundant functions during systemic acquired resistance. In two transgenic soybean lines that express PEARLI4 of A. thaliana a reduction of the diseased leaf area was observed, whilst another line showed similar susceptibility as the wildtype. Transient expression in Nicotiana benthamiana suggested localization of PEARLI4 of A. thaliana in/at the plasmamembrane. This association with the plasmamembrane might be a first hint to a possible role of PEARLI4 in penetration resistance against fungi or Phospholipase-dependent signalling in plant defense. In studies of the lipidome A. thaliana T-DNA insertion lines in P4L1 displayed reduced contents of sulfoquinovosyl diacylglycerols, phosphatidylinositols and -glycerols, whilst those accumulated in a T-DNA insertion line in P4L5. Thus, P4L1 and P4L5 might function antagonistically in the same cellular processes. The data in the present thesis substantiate the positive effect of PEARLI4 on defense against biotrophic fungi. Furthermore, the data suggest a positive role of PEARLI4 and some P4L proteins in systemic acquired resistance. Further pathogen assays might help to unravel a link between MPK defense cascades, their substrates and the subsequent cellular response. However, for further analysis possible redundancies of PEARLI4 and P4L proteins should be taken into account.