Role of Tomato Lipoxygenase D in Wound-Induced Jasmonate Biosynthesis and Plant Immunity to Insect Herbivores

Abstract

In response to insect attack and mechanical wounding, plants activate the expression of genes involved in various defense-related processes. A fascinating feature of these inducible defenses is their occurrence both locally at the wounding site and systemically in undamaged leaves throughout the plant. Wound-inducible proteinase inhibitors (PIs) in tomato (Solanum lycopersicum) provide an attractive model to understand the signal transduction events leading from localized injury to the systemic expression of defense-related genes. Among the identified intercellular molecules in regulating systemic wound response of tomato are the peptide signal systemin and the oxylipin signal jasmonic acid (JA). The systemin/JA signaling pathway provides a unique opportunity to investigate, in a single experimental system, the mechanism by which peptide and oxylipin signals interact to coordinate plant systemic immunity. Here we describe the characterization of the tomato suppressor of prosystemin-mediated responses8 (spr8) mutant, which was isolated as a suppressor of (pro)systemin-mediated signaling. spr8 plants exhibit a series of JA-dependent immune deficiencies, including the inability to express wound-responsive genes, abnormal development of glandular trichomes, and severely compromised resistance to cotton bollworm (Helicoverpa armigera) and Botrytis cinerea. Map-based cloning studies demonstrate that the spr8 mutant phenotype results from a point mutation in the catalytic domain of TomLoxD, a chloroplast-localized lipoxygenase involved in JA biosynthesis. We present evidence that overexpression of TomLoxD leads to elevated wound-induced JA biosynthesis, increased expression of wound-responsive genes and, therefore, enhanced resistance to insect herbivory attack and necrotrophic pathogen infection. These results indicate that TomLoxD is involved in wound-induced JA biosynthesis and highlight the application potential of this gene for crop protection against insects and pathogens.

Closely Related NAC Transcription Factors of Tomato Differentially Regulate Stomatal Closure and Reopening during Pathogen Attack

“…The above constructs were introduced into tomato cv M82 by Agrobacterium tumefaciens-mediated transformation (Yan et al, 2013). Transformants were selected based on their acquired resistance to hygromycin B. Homozygous T2 or T3 transgenic plants were used for phenotypic and molecular characterization.…”

“…Methyl jasmonate (MeJA), wounding, and COR treatments were performed as described previously (Uppalapati et al, 2005;Yan et al, 2013). For ABA treatment, 4-week-old tomato plants were irrigated with water containing 100 mM ABA.…”

“…Bacteria was inoculated at OD 600nm = 0.01. Tomato leaves were harvested for RNA extraction after 24 h. RNA extraction and qRT-PCR analysis were performed as described previously (Yan et al, 2013). Expression levels of target genes were normalized to those of the tomato Actin2 gene.…”

“…Free SA and ABA Measurements Free SA and ABA measurements were performed as described previously (Zhou et al, 2010;Yan et al, 2013). For free SA measurement, briefly, 4-week-old plants were vacuum-infiltrated with water or P. s. tomato DC3000 (OD 600nm = 0.01).…”

“…Oligonucleotide probes were synthesized and labeled with biotin at their 59 ends (Invitrogen). EMSA was performed as described previously Yan et al, 2013).…”