Chemokine-like MDL proteins modulate flowering time and innate immunity in plants

Abstract

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A cross‐kingdom view on the immunomodulatory role of MIF/D‐DT proteins in mammalian and plant Pseudomonas infections

“…Based on the outcome of fluorophore tagging experiments, two of the three MDL proteins (MDL1 and MDL2) have nucleo‐cytoplasmic subcellular localization in A. thaliana protoplasts, root and leaf mesophyll cells, while the third family member (MDL3), consistent with the presence of a C‐terminal PTS1 peroxisomal targeting signal, localizes to peroxisomes [85] (Figure 1). Each of the three MDL proteins can interact with itself, indicating the formation of isoform‐specific homo‐oligomers.…”

“…Each of the three MDL proteins can interact with itself, indicating the formation of isoform‐specific homo‐oligomers. In addition, MDL1 and MDL2 also interact with each other, suggesting the capacity to form also MDL1‐MDL2 hetero‐oligomers [85]. Mutants with disrupted MDL genes (knockout or knockdown mutants) exhibit a photoperiod‐dependent delay in the onset of flowering as well as enhanced antibacterial immunity (see below; [85].…”

“…In A. thaliana , insertion mutants of the three MDL genes are more resistant to the bacterial phytopathogen P. syringae pv. maculicola ( Psm ), as determined by leaf infiltration experiments using a Psm strain ( Psm lux ) that expresses a luciferase gene, which allows to quantify bacterial proliferation via its bioluminescence [85]. Based on this experimental setup, each of the Arabidopsis mdl single mutants exhibited approx.…”

“…However, bacterial infection induced changes in Arabidopsis MDL transcript and protein levels and triggers subcellular relocalization of fluorophore‐tagged MDL proteins in transgenic plant lines. The latter phenotype is characterized by the occurrence of prominent cytoplasmic MDL protein aggregates at the peripheral lobes of leaf epidermal cells [85]. In summary, MDLs have a negative regulatory role on plant defence in the context of P. syringae infection.…”

“…While P. aeruginosa PA14 has been mainly studied as a root pathogen, it is principally also able to colonize plant leaves [24]. Thus, pathologically relevant assays with Arabidopsis mdl mutants analogous to those recently reported by Gruner and colleagues [85] should be straightforward to perform and informative in their outcome. Moreover, as strain PA14 forms biofilms on Arabidopsis roots [25], this system would also allow the assessment of a putative role of MDLs in biofilm formation, and, furthermore, comparison to biofilm formation by peudomonads in mammalian lungs.…”