Transcriptional response of Arabidopsis thaliana to exogenous application of N-hydroxypipecolic acid (NHP).

Previous studies from our laboratory have shown that the resistance increase observed after biological systemic acquired resistance (SAR) induction in plants can be mimicked by exogenous plant treatment with N-hydroxypipecolic acid (NHP, Hartmann et al., 2018, Schnake et al., 2020). Moreover, exogenous application of the NHP biosynthetic precursor pipecolic acid (Pip) induced a transcriptional response that was overlapping with the SAR transcriptional response and fully depended on the NHP synthase FMO1 (Hartmann et al., 2018; E-MTAB-6243). In order to investigate whether elevations of NHP lead to a SAR-like transcriptional reprogramming, we supplied individual Arabidopsis wildtype Col-0 plants, as well as sid2-1 and npr1-3 mutant plants, with doses of 10 µmol NHP and determined the transcriptional response in leaves 24 hours later on the whole genome level by RNA-sequencing analyses in relation to control-treated (H2O) plants. Col-0 plants were additionally treated with doses of 10 µmol Pip in order to directly compare the transcriptional responses of the foliage between Pip and NHP. Arabidopsis thaliana plants were grown individually in pots containing a mixture of soil, vermiculite and sand (8:1:1) in a controlled cultivation chamber with a 10-h day (9 AM to 7 PM; photon flux density 100 mol m-2 s-1) / 14-h night cycle and a relative humidity of 70 %. Day and night temperatures were set to 21°C and 18°C, respectively. Experiments were performed with 5-week-old, naive plants exhibiting a uniform appearance. Treatments with NHP and Pip were essentially performed as detailed in Hartmann et al. (2018, Cell 173, 456–469). In brief, 10 ml of a 1 mM aqueous solution of NHP or Pip (equates to a dose of 10 µmol) were pipetted onto the soil of individually cultivated plants. 10 ml of water applied in the way served as control treatments. In total, three biologically independent, replicate experiments were performed. In each experiment, 18 full-grown leaves from 6 different plants were pooled 24 hours after the respective treatments for one biological replicate. In this way, 3 biologically independent, replicate samples per treatment and plant genotype were obtained.