Disease resistance to Pectobacterium carotovorum is negatively modulated by the Arabidopsis Lectin Receptor Kinase LecRK-V.5

Abstract

Plant stomata function in disease resistance by restricting bacteria entry inside leaves. During plant-bacteria interactions, stomatal closure is initiated by the recognition of Microbe-Associated Molecular Patterns (MAMPs). Recently, we have shown that the Lectin Receptor Kinase V.5 (LecRK-V.5) negatively regulates bacterium- and MAMP-induced stomatal closure upstream of Reactive Oxygen Species (ROS) production mediated by abscisic acid signaling. Closed stomata in lecrk-V.5 mutants are correlated with constitutive high level of ROS in guard cells. Consequently, lecrk-V.5 mutants are more resistant to hemi-biotrophic pathogen Pseudomonas syringae pv tomato DC3000 (Pst DC3000). In this report, we further investigate the role of LecRK-V.5 in resistance against necrotrophic bacteria Pectobacterium carotovorum ssp. carotovorum (Pcc). Upon surface-inoculation lecrk-V.5 mutants exhibited enhanced resistance against Pcc whereas a wild-type level of resistance was observed using infiltration-inoculation, an inoculation method that bypasses the epidermal barrier. Enhanced resistance of dip-inoculated lecrk-V.5 mutants against necrotrophic bacteria, that induce different defense responses than hemi-biotrophic bacteria, further suggests a possible role for LecRK-V.5 in stomatal immunity.

Figure 1. A negative role for LecRK-V.5 in Arabidopsis resistance to Pcc. (A) Analysis of LecRK-V.5 expression by qRT-PCR in Arabidopsis thaliana (Ler ecotype) at 0 and 1 d after dip-inoculation with 1 × 10⁵ cfu.ml⁻¹Pectobacterium carotovorum (Pcc) strain WPP14. Expression level was normalized to EF-1 and compared with time 0 with a defined expression value of 1. Data represent average values ± SE (n = 3). (B) Bacterial growth in lecrk-V.5–1 and lecrk-V.5–2 mutants and corresponding Ler and Col-0 WT plants at 1 d after dip-inoculation with 1 × 10⁵ cfu.ml⁻¹Pcc. (C) Bacterial growth in lecrk-V.5 mutants and WT (Ler and Col-0) infiltrated-inoculated with 1 × 10⁴ cfu.ml⁻¹Pcc. (D) Bacterial growth assessed at 1 d after dip-inoculation with Pcc in WT (Col-0) and LecRK-V.5 overexpression lines (OE-1 and OE-2). Bacterial quantification was determined as described earlier.^, Data represent average values ± SD. Statistical differences between WT controls and mutant or plants overexpressing LecRK-V.5 are detected with a t-test (p < 0.01, n = 6). All experiments were repeated at least twice with similar results. dpi, day post inoculation; cfu, colony forming units.