LAZARUS 1 functions as a positive regulator of plant immunity and systemic acquired resistance

Systemic acquired resistance (SAR) is activated by local infection and confers enhanced resistance against subsequent pathogen invasion. Salicylic acid (SA) and N-hydroxypipecolic acid (NHP) are two key signaling molecules in SAR and their levels accumulate during SAR activation. Two members of plant-specific Calmodulin-Binding Protein 60 (CBP60) transcription factor family, CBP60g and SARD1, regulate the expression of biosynthetic genes of SA and NHP. CBP60g and SARD1 function as master regulators of plant immunity and their expression levels are tightly controlled. Although there are numerous reports on regulation of their expression, the specific mechanisms by which SARD1 and CBP60g respond to pathogen infection are not yet fully understood. This study identifies and characterizes the role of the LAZARUS 1 (LAZ1) and its homolog LAZ1H1 in plant immunity. A forward genetic screen was conducted in the <i>sard1-1</i> mutant background to identify mutants with enhanced SAR-deficient phenotypes (<i>sard</i> mutants), leading to the discovery of <i>sard6-1</i>, which maps to the <i>LAZ1</i> gene. LAZ1 and its homolog LAZ1H1 were found to be positive regulators of SAR through regulating the expression of <i>CBP60g</i> and <i>SARD1</i> as well as biosynthetic genes of SA and NHP. Furthermore, Overexpression of <i>LAZ1</i>, <i>LAZ1H1</i> and its homologs from <i>Nicotiana benthamiana</i> and potato enhanced resistance in <i>N. benthamiana</i> against <i>Phytophthora</i> pathogens. These findings indicate that LAZ1 and LAZ1H1 are evolutionarily conserved proteins that play critical roles in plant immunity.