The Danger-associated Peps-PEPRs Regulate Root Immunity In Arabidopsis

The immune systems in plants are vitally to help plants resist pathogen invasion.The conserved chemical compositions from pathogens are termed as microbe-/pathogen-associated molecular patterns(MAMPs/PAMPs),which are perceived by the plasma membrane(PM)localized pattern recognition receptors(PRRs)in plant and activate the pattern-triggered immunity(PTI).The pathogen flagellin peptide flg22 can be perceived by the FLS2,a member belongs to the receptor-like kinases(RLKs)familiy in Arabidopsis,to trigger the immune response.In addition,the cell wall degraded products or peptides from host plants that are perceiced by the related receptors and trigger the PTI,these patterns are defined as danger-/damage-associated molecular patterns(DAMPs).In Arabidopsis,a family of endogenous plant elicitor peptides(Peps)that extracted from the C-terminal part of precursor PROPEPs proteins and perceived by a pair of receptors,PEPR1 and PEPR2,and trigger the immune responses.The Peps-PEPR has been reported to regulate the root immunity and root growth,whereas the detailed mechanism remains largely unknown.In this study,the synthetic Pepl was used and combined with pharmacological experiments to explore the Pepl effects on root immunity and growth in Arabidopsis.(1)The flg22-FLS2 and Pep1-PEPR2 regulate the root immunity and growthThe study explores the role of flg22-FLS2 and Pepl-PEPRs in root immunity.The transcriptional level of immune-related gene PDF1.2,HEL,PR1 and PAD4 were induced by Pst.DC3000 in wild type roots.The loss-of-function of FLS2,PEPR1 and PEPR2 inhibited the expression of four genes,indicates that FLS2 and PEPR function vitally in root immunity.Both of Pepl and flg22 inhibited the root growth,whereas the inhibiton rate cause by Pep1 was much stronger than flg22 did.PEPR2 primary perceived the Pepl signaling and induced the responses in roots.(2)Pep1-PEPRs induces the root prematurePepl-PEPR2 decreased the meristem size and promoted the epidermis and cortex cell changed into swelling in transition zone(TZ),the swollen cell spread transversely towards cortex and longitudinally towards the meristem zone.Meanwhile,the root hair accumulated in the swollen epidermis cell and root changed into premature.(3)The exogenous auxin phenocype the Pep1 effect on root growthThe Pepl-associated root growth independent with ABA,ethylene and cytokenins signaling pathway.The exogenous NAA and IAA enhanced the Pepl induced root growth inhibition and mimicked the Pepl effect on cell swelling and root hair formation.(4)Pepl-PEPR regulated the PIN2 and PIN3 PM location to affect root growthThe auxin efflux carriers PIN2 and PIN3 mediated the Pepl-induced local auxin accumulation.Pepl-PEPR decreased the PIN2 PM location to disrupt the basipetal auxin transportation.Furthermore,Pep1-PEPR increased the PIN3 abundance in PM of epidermis and cortex cells in TZ,which increased the horizontal auxin flowing towards TZ,induced a high content of auxin in out layers of TZ to affect root growth.(4)CLC2/3 mediates the Pepl-induced endocytosis of PIN2 and dependent on TGN/EE and PVCs trafficking pathwayCLC2 and CLC3 mediated the Pepl-PEPR-induced PIN2 endocytosis.The intracellular trafficking of PIN2 dependent on the transgolgi network/early endosome(TGN/EE)and prevacuolar compartments(PVCs)In conclusion,this study discusses Pepl-PEPR function in roots immuinity and growth.The research promotes the understanding of DAMPs in root immunity.