An activated form of NB-ARC protein RLS1 functions with cysteine-rich receptor-like protein RMC to trigger cell death in rice

A key event that follows pathogen recognition by a resistance(R)protein containing an NB-ARC(nucleotide-binding adaptor shared by Apaf-1,R proteins,and Ced-4)domain is hypersensitive response(HR)-type cell death accompanied by accumulation of reactive oxygen species and nitric oxide.However,the integral mechanisms that underlie this process remain relatively opaque.Here,we show that a gain-offunction mutation in the NB-ARC protein RLS1(Rapid Leaf Senescence 1)triggers high-light-dependent HR-like cell death in rice.The RLS1-mediated defense response is largely independent of salicylic acid accumulation,NPR1(Nonexpressor of Pathogenesis-Related Gene 1)activity,and RAR1(Required for Mla12 Resistance 1)function.A screen for suppressors of RLS1 activation identified RMC(Root Meander Curling)as essential for the RLS1-activated defense response.RMC encodes a cysteine-rich receptor-like secreted protein(CRRSP)and functions as an RLS1-binding partner.Intriguingly,their co-expression resulted in a change in the pattern of subcellular localization and was sufficient to trigger cell death accompanied by a decrease in the activity of the antioxidant enzyme APX1.Collectively,our findings reveal an NBARC-CRRSP signaling module that modulates oxidative state,the cell death process,and associated immunity responses in rice.

A cryptic inhibitor of cytokinin phosphorelay controls rice grain size

Plant hormone cytokinin signals through histidine-aspartic acid(H-D)phosphorelay to regulate plant growth and development.While it is well known that the phosphorelay involves histidine kinases,histidine phosphotransfer proteins(HPs),and response regulators(RRs),how this process is regulated by external components remains unknown.Here we demonstrate that protein phosphatase with kelch-like domains(PPKL1),known as a signaling component of steroid hormone brassinosteroid,is actually a cryptic inhibitor of cytokinin phosphorelay in rice(Oryza sativa).Mutation at a specific amino acid D364 of PPKL1 activates cytokinin response and thus enlarges grain size in a semi-dominant mutant named s48.Overexpression of PPKL1 containing D364,either with the deletion of the phosphatase domain or not,rescues the s48 mutant phenotype.PPKL1 interacts with OsAHP2,one of authentic HPs,and D364 resides in a region resembling the receiver domain of RRs.Accordingly,PPKL1 can utilize D364 to suppress OsAHP2-to-RR phosphorelay,whereas mutation of D364 abolishes the effect.This function of PPKL1 is independent of the phosphatase domain that is required for brassinosteroid signaling.Importantly,editing of the D364-residential region produces a diversity of semi-dominant mutations associated with variously increased grain sizes.Further screening of the edited plants enables the identification of two genotypes that confer significantly improved grain yield.Collectively,our study uncovers a noncanonical cytokinin signaling suppressor and provides a robust tool for seed rational design.

Modulation of nitrate-induced phosphate response by the MYB transcription factor RLI1/HINGE1 in the nucleus

The coordinated utilization of nitrogen(N)and phosphorus(P)is vital for plants to maintain nutrient balance and achieve optimal growth.Previously,we revealed a mechanism by which nitrate induces genes for phosphate utilization;this mechanism depends on NRT1.1B-facilitated degradation of cytoplasmic SPX4,which in turn promotes cytoplasmic-nuclear shuttling of PHR2,the central transcription factor of phosphate signaling,and triggers the nitrate-induced phosphate response(NIPR)and N-P coordinated utilization in rice.In this study,we unveiled a fine-tuning mechanism of NIPR in the nucleus regulated by Highly Induced by Nitrate Gene 1(HINGE1,also known as RLI1),a MYB-transcription factor closely related to PHR2.RLI1/HINGE1,which is transcriptionally activated by PHR2 under nitrate induction,can directly activate the expression of phosphate starvation-induced genes.More importantly,RLI1/HINGE1 competes with PHR2 for binding to its repressor proteins in the nucleus(SPX proteins),and consequently releases PHR2 to further enhance phosphate response.Therefore,RLI1/HINGE1 amplifies the phosphate response in the nucleus downstream of the cytoplasmic SPX4-PHR2 cascade,thereby enabling fine-tuning of N-P balance when nitrate supply is sufficient.