The apple FERONIA receptor‐like kinase MdMRLK2 negatively regulates Valsa canker resistance by suppressing defence responses and hypersensitive reaction

Abstract

Valsa canker, caused by the fungus Valsa mali, is one of the most destructive diseases of apple trees in China and other East Asian countries. The plant receptorlike kinase FERONIA is involved in plant cell growth, development, and immunity. However, little is known about the function of FERONIA in apple defence against V. mali. In this study, we found that MdMRLK2 was highly induced by V. mali in twigs of V. mali-susceptible Malus mellana but not in those of the resistant species Malus yunnaensis. 35S:MdMRLK2 apple plants showed compromised resistance relative to wild-type (WT) plants. Further analyses indicated that 35S:MdMRLK2 apple plants had enhanced abscisic acid (ABA) levels and reduced salicylic acid (SA) levels relative to the WT on V. mali infection. MdMRLK2 overexpression also suppressed polyphenol accumulation and inhibited the activities of phenylalanine ammonia-lyase (PAL), β-1,3glucanase (GLU), and chitinase (CHT) during V. mali infection. Moreover, MdMRLK2 interacted with MdHIR1, a hypersensitive-induced response protein, and suppressed the MdHIR1-mediated hypersensitive reaction (HR), probably by impairing MdHIR1 self-interaction. Collectively, these findings demonstrate that overexpression of MdMRLK2 compromises Valsa canker resistance, probably by (a) altering ABA and SA levels, (b) suppressing polyphenol accumulation, (c) inhibiting PAL, GLU, and CHT activities, and (d) blocking MdHIR1-mediated HR by disrupting MdHIR1 self-interaction.

Overexpression of the FERONIA receptor kinase MdMRLK2 enhances apple cold tolerance

“…To protect apple from freezing damage, it is important to understand better the mechanisms by which it responds to cold stress. In previous studies, we showed that MdMRLK2 ‐OE enhanced apple drought resistance (Jing et al., 2023) but compromised Valsa canker resistance (Jing et al., 2022). In this study, we discovered that MdMRLK2 ‐OE also positively affects apple cold tolerance.…”

“…“Royal Gala,” was used for apple transformation. Two transgenic lines were obtained: OE‐1 and OE‐2, with 15.2‐ and 19‐fold induction in MdMRLK2 expression, respectively (Jing et al., 2022). Tissue‐cultured “GL‐3” (WT) and MdMRLK2 ‐OE apple plants were sub‐cultured every 4 weeks.…”

Small secreted effector protein from Fusarium sacchari suppresses host immune response by inhibiting ScPi21‐induced cell death

“…The important region of Fs00367 may be used as a target region for host-induced gene silencing (HIGS)induced breeding. ScPi21 may be used for overexpression or RNAi of ROS (Levine et al, 1994), callose accumulation (Jing et al, 2022) and the high expression of immune genes (Zhang et al, 2021). In our previous study, the full length of Fs00367 was identified to suppress the cell death induced by BAX.…”

Regulation of immune complex formation and signalling by FERONIA, a busy goddess in plant–microbe interactions

“…In a recent study, MdMRLK2 , a FER homologous gene in apple, was found to be highly induced by Valsa mali in the susceptible Malus mellana , but not in the resistant Malus yunnaensis . MdMRLK2 suppressed the hypersensitive reaction by interacting with MdHIR1 and probably impairing MdHIR1 oligomerization (Figure 1 ) (Jing et al, 2022 ). Thus, FER seems to have differential roles in the responses to biotrophic, hemibiotrophic and necrotrophic pathogens.…”