Rice RING protein OsBBI1 with E3 ligase activity confers broad-spectrum resistance against Magnaporthe oryzae by modifying the cell wall defence

Abstract

Emerging evidence suggests that E3 ligases play critical roles in diverse biological processes, including innate immune responses in plants. However, the mechanism of the E3 ligase involvement in plant innate immunity is unclear. We report that a rice gene, OsBBI1, encoding a RING finger protein with E3 ligase activity, mediates broad-spectrum disease resistance. The expression of OsBBI1 was induced by rice blast fungus Magnaporthe oryzae, as well as chemical inducers, benzothiadiazole and salicylic acid. Biochemical analysis revealed that OsBBI1 protein possesses E3 ubiquitin ligase activity in vitro. Genetic analysis revealed that the loss of OsBBI1 function in a Tos17-insertion line increased susceptibility, while the overexpression of OsBBI1 in transgenic plants conferred enhanced resistance to multiple races of M. oryzae. This indicates that OsBBI1 modulates broad-spectrum resistance against the blast fungus. The OsBBI1-overexpressing plants showed higher levels of H 2 O 2 accumulation in cells and higher levels of phenolic compounds and cross-linking of proteins in cell walls at infection sites by M. oryzae compared with wild-type (WT) plants. The cell walls were thicker in the OsBBI1-overexpressing plants and thinner in the mutant plants than in the WT plants. Our results suggest that OsBBI1 modulates broad-spectrum resistance to blast fungus by modifying cell wall defence responses. The functional characterization of OsBBI1 provides insight into the E3 ligase-mediated innate immunity, and a practical tool for constructing broad-spectrum resistance against the most destructive disease in rice.

STRIPE2 Encodes a Putative dCMP Deaminase that Plays an Important Role in Chloroplast Development in Rice

“…All the leaf samples were cut into sections less than 2 mm 2 and infiltrated for 30 min with fixation buffer [2.5% glutaraldehyde in phosphate buffer (pH 7.2)] under vacuum. After 3 days at 4 C, samples were post-fixed in 0.1 mol/L cacodylate (pH 7.4) with 2% OsO 4 at 4 C, followed by washing with 0.1 mol/L PBS, then dehydrated with a gradient ethanol-acetone series and embedded in Polybed 812 (Sigma, USA) resin (Li et al, 2011). Ultrathin sections were obtained with an ultramicrotome, mounted on grids, and stained.…”

The U-Box E3 Ligase SPL11/PUB13 Is a Convergence Point of Defense and Flowering Signaling in Plants

“…Our laboratory's identification and characterization of SPL11 in rice as a U-box protein with E3 ligase activity provided, to our knowledge, the first direct evidence that ubiquitination controls resistance and PCD in rice (Zeng et al, 2004). In addition, a RING finger E3 ligase, BLAST AND BTH-INDUCED1, was found to positively regulate resistance against Magnaporthe oryzae by modifying the rice cell wall (Li et al, 2011). Another interesting protein is the RING finger E3 ligase XA21-BINDING PROTEIN3, which is required for the accumulation of the rice bacterial blight R protein XA21 and XA21-mediated defense signaling against Xanthomonas oryzae pv oryzae .…”

Tissue-Specific Ubiquitination by IPA1 INTERACTING PROTEIN1 Modulates IPA1 Protein Levels to Regulate Plant Architecture in Rice

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