A pair of G-type lectin receptor-like kinases modulates nlp20-mediated immune responses by coupling to the RLP23 receptor complex

Plant cells recognize microbial patterns with the plasma-membrane-localized pattern-recognition receptors consisting mainly of receptor kinases(RKs) and receptor-like proteins(RLPs). RKs, such as bacterial flagellin receptor FLS2, and their downstream signaling components have been studied extensively. However, newly discovered regulatory components of RLP-mediated immune signaling, such as the nlp20 receptor RLP23, await identification. Unlike RKs, RLPs lack a cytoplasmic kinase domain, instead recruiting the receptor-like kinases(RLKs) BAK1 and SOBIR1. SOBIR1 specifically works as an adapter for RLP-mediated immunity. To identify new regulators of RLP-mediated signaling, we looked for SOBIR1-binding proteins(SBPs) in Arabidopsis thaliana using protein immunoprecipitation and mass spectrometry,identifying two G-type lectin RLKs, SBP1 and SBP2, that physically interacted with SOBIR1.SBP1 and SBP2 showed high sequence similarity,were tandemly repeated on chromosome 4, and also interacted with both RLP23 and BAK1. sbp1 sbp2 double mutants obtained via CRISPR-Cas9 gene editing showed severely impaired nlp20-induced reactive oxygen species burst, mitogenactivated protein kinase(MAPK) activation, and defense gene expression, but normal flg22-induced immune responses. We showed that SBP1 regulated nlp20-induced immunity in a kinase activityindependent manner. Furthermore, the nlp20-induced the RLP23–BAK1 interaction, although not the flg22-induced FLS2–BAK1 interaction, was significantly reduced in sbp1 sbp2. This study identified SBPs as new regulatory components in RLP23 receptor complex that may specifically modulate RLP23-mediated immunity by positively regulating the interaction between the RLP23 receptor and the BAK1 co-receptor.

CPR5 positively regulates pattern-triggered immunity via a mediator protein

Plant cells possess a two-layered immune system consisting of pattern-triggered immunity(PTI)and effector-triggered immunity(ETI), mediated by cell surface pattern-recognition receptors and intracellular nucleotide-binding leucine-rich repeat receptors(NLRs), respectively. The CONSTITUTIVE EXPRESSION OF PR GENES 5(CPR5) nuclear pore complex protein negatively regulates ETI, including ETI-associated hypersensitive response. Here, we show that CPR5 is essential for the activation of various PTI responses in Arabidopsis, such as resistance to the non-adapted bacterium Pseudomonas syringae pv. tomato DC3000 hrc C-. In a forward-genetic screen for suppressors of cpr5, we identified the mediator protein MED4. Mutation of MED4 in cpr5 greatly restored the defective PTI of cpr5. Our findings reveal that CPR5 plays opposite roles in regulating PTI and ETI, and genetically regulates PTI via MED4.

Regulation of plant responses to biotic and abiotic stress by receptor-like cytoplasmic kinases

As sessile organisms,plants have to cope with environmental change and numerous biotic and abiotic stress.Upon perceiving environmental cues and stress signals using different types of receptors,plant cells initiate immediate and complicated signaling to regulate cellular processes and respond to stress.Receptor-like cytoplasmic kinases(RLCKs)transduce signals from receptors to cellular components and play roles in diverse biological processes.Recent studies have revealed the hubbing roles of RLCKs in plant responses to biotic stress.Emerging evidence indicates the important regulatory roles of RLCKs in plant responses to abiotic stress,growth,and development.As a pivot of cellular signaling,the activity and stability of RLCKs are dynamically and tightly controlled.Here,we summarize the current understanding of how RLCKs regulate plant responses to biotic and abiotic stress.

The secret of fertilization in flowering plants unveiled

As recapitulated in the famous Chinese fairy tale Journey to the West,the Buddhist monk Xuanzang of the Tang Dynasty(Tangseng)took a heroic journey in a quest for India Buddhist sacred scriptures.The long and dangerous journey was made possible only with the help of the powerful Monkey King,who had been pinned down under a mountain by the Buddha as a punishment for his prior misdemeanor.The Buddha had to secure the