Phytocytokines function as immunological modulators of plant immunity

Plant plasma membrane-resident immune receptors regulate plant immunity by recognizing microbe-associated molecular patterns(MAMPs),damage-associated molecular patterns(DAMPs),and phytocytokines.Phytocytokines are plant endogenous peptides,which are usually produced in the cytosol and released into the apoplast when plant encounters pathogen infections.Phytocytokines regulate plant immunity through activating an overlapping signaling pathway with MAMPs/DAMPs with some unique features.Here,we highlight the current understanding of phytocytokine production,perception and functions in plant immunity,and discuss how plants and pathogens manipulate phytocytokine signaling for their own benefits during the plant-pathogen warfare.

Arabidopsis RNA polymerase Ⅱ C-terminal domain phosphatase-like 1 targets mitogen-activated protein kinase cascades to suppress plant immunity

Mitogen-activated protein kinase(MAPK) cascades play pivotal roles in plant defense against phytopathogens downstream of immune receptor complexes. The amplitude and duration of MAPK activation must be strictly controlled, but the underlying mechanism remains unclear. Here, we identified Arabidopsis CPL1(C-terminal domain phosphatase-like 1)as a negative regulator of microbe-associated molecular pattern(MAMP)-triggered immunity via a forward-genetic screen. Disruption of CPL1 significantly enhanced plant resistance to Pseudomonas pathogens induced by the bacterial peptide fg22. Furthermore, fg22-induced MPK3/MPK4/MPK6 phosphorylation was dramatically elevated in cpl1 mutants but severely impaired in CPL1 overexpression lines, suggesting that CPL1 might interfere with fg22-induced MAPK activation. Indeed, CPL1 directly interacted with MPK3 and MPK6, as well as the upstream MKK4 and MKK5. A firefy luciferase-based complementation assay indicated that the interaction between MKK4/MKK5 and MPK3/MPK6 was significantly reduced in the presence of CPL1. These results suggest that CPL1 plays a novel regulatory role in suppressing MAMP-induced MAPK cascade activation and MAMP-triggered immunity to bacterial pathogens.

Roles of small RNAs in plant disease resistance

The interaction between plants and pathogens represents a dynamic competition between a robust immune system and efficient infectious strategies. Plant innate immunity is composed of complex and highly regulated molecular networks, which can be triggered by the perception of either conserved or race-specific pathogenic molecular signatures. Small RNAs are emerging as versatile regulators of plant development, growth and response to biotic and abiotic stresses. They act in different tiers of plant immunity, including the pathogen-associated molecular pattern-triggered and the effector-triggered immunity. On the other hand, pathogens have evolved effector molecules to suppress or hijack the host small RNA pathways. This leads to an arms race between plants and pathogens at the level of small RNA-mediated defense. Here, we review recent advances in small RNA-mediated defense responses and discuss the challenging questions in this area.