Two VQ Proteins are Substrates of the OsMPKK6-OsMPK4 Cascade in Rice Defense Against Bacterial Blight

Abstract

Background The plant-specific valine-glutamine (VQ) protein family with the conserved motif FxxxVQxLTG reportedly functions with the mitogen-activated protein kinase (MAPK) in plant immunity. However, the roles of VQ proteins in MAPK-mediated resistance to disease in rice remain largely unknown. Results In this study, two rice VQ proteins OsVQ14 and OsVQ32 were newly identified to function as the signaling components of a MAPK cascade, OsMPKK6-OsMPK4, to regulate rice resistance to Xanthomonas oryzae pv. oryzae (Xoo). Both OsVQ14 and OsVQ32 positively regulated rice resistance to Xoo. In vitro and in vivo studies revealed that OsVQ14 and OsVQ32 physically interacted with and were phosphorylated by OsMPK4. OsMPK4 was highly phosphorylated in transgenic plants overexpressing OsMPKK6, which showed enhanced resistance to Xoo. Meanwhile, phosphorylated OsVQ14 and OsVQ32 were also markedly accumulated in OsMPKK6-overexpressing transgenic plants. Conclusions We discovered that OsVQ14 and OsVQ32 functioned as substrates of the OsMPKK6-OsMPK4 cascade to enhance rice resistance to Xoo, thereby defining a more complete signal transduction pathway for induced defenses.

Mitogen-Activated Protein Kinase and Substrate Identification in Plant Growth and Development

“…In addition, OsMKK10-2-OsMPK6 responds to SA-mediated plant pathogen defense responses through the phosphorylation of WRKY45 [ 72 ], and OsRLCK185 (receptor-like cytoplasmic kinase) converts immune signals perceived by PAMP effector rice chitin elicitor receptor kinase 1 (OsCERK1) and activates the downstream OsMAPKKKε–OsMKK4–OsMPK3/6 pathway [ 73 ]. Studies have also shown that OsMKK3–OsMPK7–OsWRKY30 and OsMKKK43-OsMKK4–OsMPK6 can promote rice bacterial blight resistance [ 74 , 75 , 76 ], while OsMPK15 plays a negative role in Magnaporthe oryza and Xoo tolerance through the SA and JA signaling pathways [ 77 ]. The OsMKK2–OsMPK1 module positively regulates ROS-dependent blast disease (susceptibility)-related cell death in M. oryzae infection [ 78 ].…”

“…Moreover, the newly identified MPK4 substrate is a transcription suppressor, ASR3 (ARABIDOPSIS SH4-RELATED3), which can enhance its DNA binding after phosphorylation by MPK4, thus inhibiting gene expression [ 125 ]. Some research has also indicated that OsVQ14 (valine-glutamine) and OsVQ32 act as substrates of the OsMPKK6–OsMPK4 cascade to improve rice tolerance to Xoo [ 76 ]. OsMPK4 phosphorylates OsVQ14 and OsVQ32 and can interact with them in vitro and in vivo.…”

OsVQ1 links rice immunity and flowering via interaction with a mitogen-activated protein kinase OsMPK6

“…In rice plants, jasmonic acid-responsive OsVQ13 interacted with OsMPK6 and activated the OsMPK6-OsWRKY45 signaling pathway to promote rice resistance to bacterial pathogen (Uji et al 2019). OsVQ14 and OsVQ32 functioned as the substrates of the OsMPKK6-OsMPK4 cascade in rice defense against bacterial blight (Li et al 2021). These findings suggested that the relationship between MAPK and VQ is complex and needs further clarification.…”

“…Our previous study analyzed the expression of VQ genes in rice-pathogen interactions and found that some VQ genes were involved in rice disease resistance (Li et al 2014(Li et al , 2021. Here, we characterized the function of OsVQ1 in rice disease resistance against two Xanthomonas oryzae pathovars, X. oryzae pv.…”

OsMAPK6 phosphorylates a zinc finger protein OsLIC to promote downstream OsWRKY30 for rice resistance to bacterial blight and leaf streak

“…The activated MAPKs fulfill their function by phosphorylating specific downstream substrates, including transcription factors, enzymes and chromatin remodeling factors, resulting in the signal transduction (Bigeard and Hirt, 2018; Doczi and Bogre, 2018). Several rice MAPK cascades have been validated involving in rice immunity by phosphorylating different downstream substrates: OsMAPKK10.2‐OsMAPK6 cascade phosphorylates OsWRKY45, and OsMAPKK4‐OsMAPK6 cascade phosphorylates OsWRKY53 and Oryza sativa Rac Immunity 1 (OsRAI1) to trigger rice resistance to fungal blast (Kim et al, 2012; Ueno et al, 2013, 2015; Chujo et al, 2014), OsMAPKK6‐OsMAPK4 cascade phosphorylates OsVQ14 and OsVQ32, and OsMAPKK3‐OsMAPK7 cascade phosphorylates OsWRKY30 to confer rice resistance to bacterial blight (Jalmi and Sinha, 2016; Li et al, 2021). However, OsMAPK6‐phosphorylated downstream components conferring rice against bacterial pathogens have not yet been identified.…”