JAZ repressors of metabolic defense promote growth and reproductive fitness in Arabidopsis

Abstract

Plant immune responses mediated by the hormone jasmonoyl-l-isoleucine (JA-Ile) are metabolically costly and often linked to reduced growth. Although it is known that JA-Ile activates defense responses by triggering the degradation of JASMONATE ZIM DOMAIN (JAZ) transcriptional repressor proteins, expansion of the JAZ gene family in vascular plants has hampered efforts to understand how this hormone impacts growth and other physiological tasks over the course of ontogeny. Here, we combined mutations within the 13-member Arabidopsis JAZ gene family to investigate the effects of chronic JAZ deficiency on growth, defense, and reproductive output. A higher-order mutant (jaz decuple, jazD) defective in 10 JAZ genes (JAZ1-7, -9, -10, and -13) exhibited robust resistance to insect herbivores and fungal pathogens, which was accompanied by slow vegetative growth and poor reproductive performance. Metabolic phenotypes of jazD discerned from global transcript and protein profiling were indicative of elevated carbon partitioning to amino acid-, protein-, and endoplasmic reticulum body-based defenses controlled by the JA-Ile and ethylene branches of immunity. Resource allocation to a strong defense sink in jazD leaves was associated with increased respiration and hallmarks of carbon starvation but no overt changes in photosynthetic rate. Depletion of the remaining JAZ repressors in jazD further exaggerated growth stunting, nearly abolished seed production and, under extreme conditions, caused spreading necrotic lesions and tissue death. Our results demonstrate that JAZ proteins promote growth and reproductive success at least in part by preventing catastrophic metabolic effects of an unrestrained immune response.

Keywords: carbon starvation; growth–defense trade-off; jasmonate; plant immunity; plant-insect interaction.

Fig. 1.

A jaz decuple mutant (jazD) is highly sensitive to jasmonate and exhibits reduced growth and fertility. (A) Root length of 8-d-old WT Col-0 (WT), jazQ, and jazD seedlings grown in the presence of 0, 5, or 25 µM MeJA. Data show the mean ± SD of 30 plants per genotype at each concentration. Capital letters denote significant differences according to Tukey’s honest significant difference (HSD) test (P < 0.05). (B) jazD leaves are hypersensitive to COR. The eighth leaf of 40-d-old plants grown under 12-h light/12-h dark photoperiod was treated with 5 µL water (mock) or 50 µM COR. Leaves were excised and photographed after 2 or 4 d of treatment. Arrows denote location of visible anthocyanin accumulation at the site of COR application. Inset, Right is enlargement of photograph of the COR-treated jazD. (Scale bars: 1 cm.) (C) RGR of soil-grown WT, jazQ, and jazD plants. (D) Total fatty acid content in seeds from the indicated genotype. Data show the mean ± SD of seeds obtained from five plants per genotype. (E) Time course of seed germination. Colored bars indicate the percentage of germinated seeds at various times after sowing on water agar: white, day 1; gray, day 2; black, day 3 and all later times; red, nongerminated seeds.

Fig. 2.

jazD plants are highly resistant to insect herbivores and necrotrophic pathogens. (A) Representative short-day grown WT Col-0 (WT), jazQ, and jazD plants before and after challenge with four T. ni larvae for 12 d. (Scale bar: 3 cm.) (B) Weight gain of T. ni larvae reared on plants shown in A. Data show the mean ± SD of at least 30 larvae per genotype. Capital letters denote significant differences according to Tukey’s HSD test (P < 0.05). (C) Heat map displaying the expression level of various jasmonate/ethylene-responsive genes in leaves of jazQ and jazD normalized to WT. ACT, agmatine coumaroyltransferase (At5g61160). (D) Representative leaf symptoms following 5 d treatment with B. cinerea spores or mock solution. (Scale bars: 2 cm.) (E) Disease lesion size on leaves of the indicated genotype. Data show the mean ± SD of at least 19 leaves per genotype. Capital letters denote significant differences (Tukey’s HSD test, P < 0.05). (F) Apical hook angle of seedlings grown in the presence of various concentrations of the ethylene precursor ACC. Data show the mean ± SD of at least 21 seedlings per genotype. Asterisks denote significant difference compared with WT (Tukey’s HSD test, *P < 0.05).

Fig. 3.

Reconfiguration of primary and secondary metabolism in jazD. (A) Mapping of differentially regulated genes in jazD to various metabolic pathways implicates elevated production of defense metabolites derived from amino acids. Mapped pathways include photosynthesis (1), pentose phosphate pathway (2), shikimate pathway (3), amino acids from pentose phosphate intermediates (4), glycolysis (5), amino acids from glycolysis intermediates (6), TCA cycle (7), amino acids from TCA intermediates (8), sulfur metabolism (9), and defense metabolites from amino acids (10). Colored arrows denote the average fold-change of differentially expressed transcripts mapping to a particular pathway (P < 0.05) (Dataset S3). (B) Schematic of tryptophan biosynthesis from erythrose 4-phosphate (E4P), phosphoenolpyruvate (PEP), and 3-phosphoglycerate (3PG) illustrates up-regulation of genes and proteins in jazD. Each arrow represents an enzymatic reaction in the pathway. Boxes represent individual genes, colored by fold-change of jazD relative to WT according to RNA-seq data (Dataset S3), whereas gray boxes denote genes with no significant change in expression. Gene names within boxes denote significantly increased protein levels according to proteomics data. Gene abbreviations: AnPRT, anthranilate phosphoribosyltransferase; AS, anthranilate synthase; CS, chorismate synthase; DHQS, 3-dehydroquinate synthase; DHS, 3-deoxy-7-phosphoheptulonate synthase; DQD/SDH, 3-dehydroquinate dehydratase/shikimate dehydrogenase; EPSP, 5-enolpyruvylshikimate-3-phosphate synthase; IGPS, indole-3-glycerol-phosphate synthase; IGs, indole glucosinolates; OAS, O-acetylserine lyase; PAI, phosphoribosylanthranilate isomerase; PGDH, phosphoglycerate dehydrogenase; PSAT, phosphoserine aminotransferase; PSP, phosphoserine phosphatase; SAT, serine acetyltransferase; SK, shikimate kinase; TSA, tryptophan synthase alpha subunit; TSB, tryptophan synthase β-subunit. (C) Indole glucosinolate levels in jazD leaves relative to that in WT leaves. Asterisks denote significant differences in comparison with WT (Student’s t test, *P < 0.05). Abbreviations: 1MOI3M, 1-methoxyindol-3-ylmethyl (neoglucobrassicin); 4MOI3M, 4-methoxyindol-3-ylmethyl (methoxyglucobrassicin); I3M, indol-3-ylmethyl (glucobrassicin); OH-I3M, 4-hydroxyindol-3-ylmethyl (hydroxyglucobrassicin). (D and E) Net gas exchange rate in WT and jazD rosette leaves measured at 400 µmol CO₂ and 20 °C after acclimation in 500 μmol m⁻² s⁻¹ in light (D) or dark (E).

Fig. 4.

jazD plants exhibit symptoms of carbon starvation. (A and B) Time course of starch (A) and sucrose (B) levels in WT Col-0 (WT) and jazD plants during long-day photoperiod. Asterisks denote significant differences in comparison with WT (Student’s t test, *P < 0.05). (C) Heat map showing the expression level of SSM genes in jazQ and jazD leaves. Gene-expression levels determined by RNA-seq are represented as fold-change (log₂) over WT. (D and E) Photograph (D) and DW (E) of 16-d-old WT, jazQ, and jazD seedlings grown horizontally on MS medium containing the indicated concentration of sucrose. (Scale bar: D, 0.5 cm.) (F) Root length of 11-d-old WT, jazQ, and jazD seedlings grown vertically on MS medium lacking sucrose (open bar) or containing 23 mM sucrose (filled bar). Two-way ANOVA was used to test the effect of sucrose on growth (E and F) and showed that, whereas genotype (P < 0.001 for both WT vs. jazQ and WT vs. jazD) and sucrose (P < 0.001 for both WT vs. jazQ and WT vs. jazD) significantly affect shoot and root growth, the genotype × sucrose interaction was significant only for jazD comparisons.

Fig. 5.

Genetic combination of jaz8 and jazD further restricts growth and nearly abolishes seed production in the resulting undecuple mutant. (A) Root length of 10-d-old WT Col-0 (WT), jazD, and jaz undecuple (jazU) seedlings grown in the presence of 0, 0.2, or 1 µM MeJA. Data show the mean ± SD of 14–20 seedlings per genotype at each concentration. Capital letters denote significant differences according to Tukey’s HSD test (P < 0.05). (B) Photograph of WT, jazQ, jazD, and jazU rosettes of 28-d-old plants. (C) Photograph of WT, jazD, and jazU inflorescence of 8-wk-old plants.