Hypersensitive response-like cell death and its key related genes in the lmd lesion mimic mutant of birch

Abstract

Lesion mimic mutants (LMMs) often display hypersensitive response-like (HR-like) cell death and enhanced resistance to pathogens. LMMs have been viewed as useful for the study of the mechanism of cell death and plant immunity. To date, few LMMs have been found in woody plants. We previously identified an LMM termed lmd, which showed spontaneous cell death in birch. In the current study, we investigated lmd, oe21 (transgenic control), and NT (nontransgenic control), focusing on cell death and gene expression profile of lmd. We found that cell death in the lmd occurred gradually during leaf development. The number of necrotic spots increased as the leaf developed, with no significant change in spot size. Subcellular observations showed degradation of both mitochondria and chloroplasts in lmd cells but not in NT and oe21 cells. Autophagosomes were visible in dying cells of lmd. We then performed RNA-seq of the four most apical leaves of lmd and oe21 to explore the gene expression profile during cell death. Genes that were functional in signal perception, respiratory burst, signal transduction, and defense were enriched. TGA1,  WRKY33,  WRKY40,  Chitinase,  FLS2,  RbohA/D, and SBT were identified as key genes involved in cell death in lmd.