Differential innate immune signalling via Ca(2+) sensor protein kinases

Area of Science:

• Plant biology
• Immunology
• Molecular signaling

Background:

• Innate immunity is the first defense against pathogens in plants and animals.
• Microbe-associated molecular patterns (MAMPs) trigger conserved signaling pathways, including MAPK cascades.
• Calcium (Ca2+) is a key mediator in plant defense, but its sensing and signaling in early MAMP responses remain unclear.

Purpose of the Study:

• To identify Ca2+-sensor proteins involved in plant innate immune signaling.
• To elucidate the role of CDPKs in MAMP-triggered transcriptional reprogramming.
• To understand the interplay between CDPKs, MAPK cascades, and early defense gene activation.

Main Methods:

• Functional genomic screening to identify key genes.
• Genome-wide gene expression profiling (transcriptome analysis).
• Generation and analysis of multiple cpk mutant plants (double, triple, quadruple).

Main Results:

• Four calcium-dependent protein kinases (CDPKs) were identified as critical Ca2+-sensor proteins for transcriptional reprogramming in plant innate immunity.
• CDPKs and MAPK cascades differentially regulate MAMP-mediated programs, affecting defense peptides, metabolites, cell wall modifications, and redox signaling.
• Mutant analysis revealed that CDPKs are essential for oxidative burst, early gene activation (e.g., by flg22), and pathogen defense, with increasing severity in higher-order mutants.

Conclusions:

• CDPKs act as crucial convergence points for signaling triggered by various MAMPs.
• This study highlights the complex role of Ca2+ signaling in plants, revealing essential positive functions of specific CDPKs in initiating MAMP signaling pathways.
• CDPKs are vital positive regulators of plant innate immunity, distinct from previously described negative regulators like calmodulin.