Bacterial Compound N,N-Dimethylhexadecylamine Modulates Expression of Iron Deficiency and Defense Response Genes in Medicago truncatula Independently of the Jasmonic Acid Pathway

Abstract

Plants face a variety of biotic and abiotic stresses including attack by microbial phytopathogens and nutrient deficiencies. Some bacterial volatile organic compounds (VOCs) activate defense and iron-deficiency responses in plants. To establish a relationship between defense and iron deficiency through VOCs, we identified key genes in the defense and iron-deprivation responses of the legume model Medicago truncatula and evaluated the effect of the rhizobacterial VOC N,N-dimethylhexadecylamine (DMHDA) on the gene expression in these pathways by RT-qPCR. DMHDA increased M. truncatula growth 1.5-fold under both iron-sufficient and iron-deficient conditions compared with untreated plants, whereas salicylic acid and jasmonic acid decreased growth. Iron-deficiency induced iron uptake and defense gene expression. Moreover, the effect was greater in combination with DMHDA. Salicylic acid, Pseudomonas syringae, jasmonic acid, and Botrytis cinerea had inhibitory effects on growth and iron response gene expression but activated defense genes. Taken together, our results showed that the VOC DMHDA activates defense and iron-deprivation pathways while inducing a growth promoting effect unlike conventional phytohormones, highlighting that DMHDA does not mimic jasmonic acid but induces an alternative pathway. This is a novel aspect in the complex interactions between biotic and abiotic stresses.

Microbial enhancement of plant nutrient acquisition

“…The volatile compound N,N-dimethylhexadecylamine (DMHDA), which is commonly produced by several bacteria strains belonging to Arthrobacter agilis, Sinorhizobium meliloti, or Pseudomonas fluorescens, was shown to induce plant Fe-deficiency responses (del Carmen Orozco-Mosqueda et al 2013a, Castulo-Rubio et al 2015, Montejano-Ramírez et al 2020. GB03 VOCs' effects on plant Fe-acquisition requires transcriptional induction of FIT1 (Zhang et al 2009), a master regulator of Fe-deficiency responses conserved in plants (Riaz and Guerinot 2021).…”

Comparative genomic and functional analysis of Arthrobacter sp. UMCV2 reveals the presence of luxR-related genes inducible by the biocompound N, N-dimethylhexadecilamine

“…Plant organogenesis and growth are modulated by DMHDA through modifying the balance between stem cell niche and Jasmonic acid-dependent gene expression ( Vázquez-Chimalhua et al, 2021b ). DMHDA also induces expression of genes involved in plant systemic defense mechanisms and Fe-acquisition strategies, which are suggested to enhance photosynthesis and biomass production ( Orozco-Mosqueda et al, 2013 ; Castulo-Rubio et al, 2015 ; Montejano-Ramírez et al, 2020 ). Previous results showed that Arthrobacter sp.…”

Rhizobial Volatiles: Potential New Players in the Complex Interkingdom Signaling With Legumes

“…The coordinated activation of the iron-deficiency and defense responses in plants has also been shown in legumes exposed to pure volatiles. Medium supplemented with N,N -dimethylhexadecylamine (DMHDA), a volatile produced during the co-cultivation of S. meliloti and M. truncatula ( Orozco-Mosqueda et al, 2013 ), has been shown to promote plant growth and induce iron-deficiency and defense response genes in M. truncatula ( Montejano-Ramírez et al, 2020 ). However, effects of either DMHDA or volatile blends of rhizobia in the establishment of the Rhizobium -legume symbiosis have not been reported yet.…”