Differential phosphorylation of Ca2+-permeable channel CNGC20 modulates calcium-mediated freezing tolerance in Arabidopsis.

Plants respond to cold stress at multiple levels, including increasing cytosolic calcium (Ca2+) influx and triggering the expression of cold-responsive genes. Here we show that the Ca2+-permeable channel CYCLIC NUCLEOTIDE GATED CHANNEL20 (CNGC20) positively regulates freezing tolerance in Arabidopsis (Arabidopsis thaliana) by mediating cold-induced Ca2+ influx. Moreover, we demonstrate that the leucine-rich repeat receptor-like kinase PLANT PEPTIDE CONTAINING SULFATED TYROSINE1 RECEPTOR (PSY1R) is activated by cold, phosphorylating and enhancing the activity of CNGC20. The psy1r mutant exhibited decreased cold-evoked Ca2+ influx and freezing tolerance. Conversely, COLD-RESPONSIVE PROTEIN KINASE1 (CRPK1), a protein kinase that negatively regulates cold signaling, phosphorylates and facilitates the degradation of CNGC20 under prolonged periods of cold treatment, thereby attenuating freezing tolerance. This study thus identifies PSY1R and CRPK1 kinases that regulate CNGC20 activity and stability, respectively, thereby antagonistically modulating freezing tolerance in plants.

The Arabidopsis mature endosperm promotes seedling cuticle formation via release of sulfated peptides.

In Arabidopsis mature seeds, the onset of the embryo-to-seedling transition is nonautonomously controlled, being blocked by endospermic abscisic acid (ABA) release under unfavorable conditions. Whether the mature endosperm governs additional nonautonomous developmental processes during this transition is unknown. Mature embryos have a more permeable cuticle than seedlings, consistent with their endospermic ABA uptake capability. Seedlings acquire their well-sealing cuticles adapted to aerial lifestyle during germination. Endosperm removal prevents seedling cuticle formation, and seed reconstitution by endosperm grafting onto embryos shows that the endosperm promotes seedling cuticle development. Grafting different endosperm and embryo mutant combinations, together with biochemical, microscopy, and mass spectrometry approaches, reveal that the release of tyrosylprotein sulfotransferase (TPST)-sulfated CIF2 and PSY1 peptides from the endosperm promotes seedling cuticle development. Endosperm-deprived embryos produced nonviable seedlings bearing numerous developmental defects, not related to embryo malnutrition, all restored by exogenously provided endosperm. Hence, seedling establishment is nonautonomous, requiring the mature endosperm.

PSKR1 and PSY1R-mediated regulation of plant defense responses.

Plant peptide signaling is an upcoming topic in many areas of plant research. Our recent findings show that the tyrosine sulfated peptide receptors PSKR1 and PSY1R are not only involved in growth and development but also in plant defense. They modulate salicylate- and jasmonate-dependent defense pathways in an antagonistic manner and this phenomenon might be dependent on the age and developmental stage of the plant. Here we discuss how the endogenous peptides might integrate growth, wounding, senescence and the opposing defense pathways against biotrophic and necrotrophic pathogens for increased fitness of the plant.