The hydroxyproline-rich glycopeptide systemin precursor NapreproHypSys does not play a central role in Nicotiana attenuata's anti-herbivore defense responses

To determine whether the Nicotiana tabacum preproHypSys homolog in Nicotiana attenuata (NapreproHypSys) mediates anti-herbivore responses, we silenced (IRsys) and ectopically over-expressed (OVsys) NapreproHypSys in N. attenuata. Neither herbivore simulation nor methyl jasmonate (MeJA) application increased transcripts in wild-type (WT) or transformed lines. Compared to WT plants, OVsys plants had marginally higher constitutive levels but normally induced levels of trypsin proteinase inhibitors (TPIs) and nicotine; IRsys plants did not differ from WT plants. Herbivory-associated signalling [salicylic acid-induced protein kinase (SIPK) activity, jasmonic acid (JA), jasmonic acid-isoleucine/leucine (JA-Ile/Leu) and ethylene production or perception] did not differ strongly among the lines, but JA, JA-Ile/Leu and ethylene were marginally higher in OVsys plants. Manduca sexta larval performance did not differ among the lines, but feeding induced levels of TPI and nicotine in OVsys plants and decreased them in IRsys plants relative to WT. The secondary metabolite profiles of plants transplanted into N. attenuata's native habitat in the Great Basin Desert (UT, USA) mirrored those of glasshouse-grown plants, and compared to WT plants, OVsys plants suffered marginally less damage from grasshoppers, mirids and flea beetles but did not differ in their ability to attract Geocoris predators. We conclude that NapreproHypSys does not play a central role in anti-herbivore defense signalling in this native tobacco.