OsWRKY53, a versatile switch in regulating herbivore-induced defense responses in rice

Abstract

WRKY proteins, which belong to a large family of plant-specific transcription factors, play important roles in plant defenses against pathogens and herbivores by regulating defense-related signaling pathways. Recently, a rice WRKY transcription factor OsWRKY53 has been reported to function as a negative feedback modulator of OsMPK3/OsMPK6 and thereby to control the size of the investment a rice plant makes to defend against a chewing herbivore, the striped stem borer Chilo suppressalis. We investigated the performance of a piecing-sucking herbivore, the brown planthopper (BPH) Nilaparvata lugens, on transgenic plants that silence or overexpress OsWRKY53, and found that OsWRKY53 activates rice defenses against BPH by activating an H2O2 burst and suppressing ethylene biosynthesis. These findings suggest that OsWRKY53 functions not only as a regulator of plants' investment in specific defenses, but also as a switch to initiate new defenses against other stresses, highlighting the versatility and importance of OsWRKY53 in herbivore-induced plant defenses.

Keywords: Ethylene; H2O2; Nilaparvata lugens; OsWRKY53; plant defense response; rice.

Figure 1.

OsWRKY53 positively regulates the ability of rice to resist brown planthopper (BPH). (A) Mean transcript levels (+SE, n = 5) of OsWRKY53 in rice stems that were infested by 15 gravid female BPH adults. Non-infested plant stems were covered with an empty glass cage. Transcript levels were analyzed by quantitative RT-PCR. Asterisks represent significant differences between treatments and controls at the indicated times (2-way analysis of variance, followed by pairwise comparisons of least squares means (LSM), P values were corrected by the false discovery rate (FDR) method; *, P< 0.05). (B) Oviposition marks (a, indicated by arrows), eggs (b) and female adults (c) of BPH. (C) to (F) Mean number of female BPH adults per plant (+SE, n = 10) on pairs of plants (wild type (WT) versus ir-14, ir-29, oe-5 and oe-6, respectively), 1–48 h after pairs were exposed to insects. Inserts: mean percentage (+SE, n = 10) of BPH eggs per plant on pairs of plants as stated above, 48 h after the release of BPH. Asterisks indicate a significant preference within each combination and time point (Wald test, *, P < 0.05, **, P < 0.01). (G) and (H) Mean survival rate (+SE, n = 10) of BPH nymphs that fed on ir-wrky lines, oe-WRKY lines or WT plants 1-12 d after the start of feeding. Inserts: mean hatching rate (+SE, n = 6) of BPH eggs on ir-wrky lines, oe-WRKY lines or WT plants. Asterisks represent significant differences between transgenic lines and WT plants (generalized linear model [family: Binomial or Quasibinomial], followed by pairwise comparisons of LSM, P values were corrected by FDR method;*, P < 0.05, **, P < 0.01). (I) and (J) Damaged phenotypes of ir-wrky, oe-WRKY lines and WT plants that were individually infested by 15 BPH female adults for 11 (I) or 18 (J) days (n = 20).

Figure 2.

Exogenous application of H₂O₂ complements resistance to rice brown planthopper (BPH) in ir-wrky lines. (A) and (B) Mean levels (+SE, n = 5) of H₂O₂ (A) and ethylene (B) in ir-wrky and oe-WRKY lines and in wild-type (WT) plants that were individually infested by 15 female BPH adults. FW, fresh weight. Asterisks indicate significant differences in ir-wrky and oe-WRKY lines compared with WT plants (2-way analysis of variance , followed by pairwise comparisons of least squares means, P values were corrected by the false discovery rate method; *, P < 0.05, **, P < 0.01). (C) to (F) Mean number of adult female BPH per plant (+SE, n = 10) on pairs of plants, WT plants treated with 400 μL of 20 mM sodium phosphate buffer (pH 6.5) vs. ir-14 plants treated with 400 μL of the buffer (C), ir-14 plants treated with 400 μL of Glc (25 mM) in the buffer (D), ir-14 plants treated with 400 μL of GOX (50 units mL^-1) in the buffer (E), and ir-14 plants treated with 400 μL of GOX (50 units mL⁻¹) and Glc solution (25 mM) in the buffer (F), respectively, 1–48 h after the release of female adults. Inserts: mean percentage (+SE, n = 10) of BPH eggs per plant on pairs of plants as stated above, 48 h after the release of BPH. Buf, buffer; Glc, glucose; GOX, glucose oxidase. Asterisks indicate a significant preference within each combination and time point (Wald test, *P < 0.05; **P < 0.01).