A Constitutive Shade-Avoidance Mutant Implicates TIR-NBS-LRR Proteins in Arabidopsis Photomorphogenic Development

ANA FAIGÓN-SOVERNA; FRANKLIN G. HARMON; LEONARDO STORANI; ELIZABETH KARAYEKOV; ROBERTO J. STANELONI; WALTER GASSMANN; PALOMA MÁS; JORGE J. CASAL

PLANT CELL

Año: 2006 p. 2919 - 2928

1040-4651

In plants, light signals caused by the presence of neighbors accelerate stem growth and flowering and induce a more erect position of the leaves, a developmental strategy known as shade-avoidance syndrome. In addition, mutations in the photoreceptors that mediate shade-avoidance responses enhance disease susceptibility in Arabidopsis thaliana. Here, we describe the Arabidopsis constitutive shade-avoidance1 (csa1) mutant, which shows a shade-avoidance phenotype in the absenceof shade and enhancedgrowthof a bacterial pathogen. The csa1mutant has a T-DNAinsertedwithinthe secondexon of a Toll/Interleukin1 receptor–nucleotide binding site–leucine-rich repeat (TIR-NBS-LRR) gene, which leads to the production of a truncated mRNA. Arabidopsis plants transformed with the truncated TIR-NBS-LRR gene recapitulate the mutant phenotype,indicating that csa1 is a dominant-negative mutation that interferes with phytochrome signaling. TIR-NBS-LRR proteins have been implicated in defense responses in plants. RPS4, the closest hhomolog of CSA1, confers resistance to Pseudomonas syringae and complements the csa1 mutant phenotype, indicating that responses to pathogens and neighbors share coresignaling components in Arabidopsis. In Drosophila melanogaster and Caenorhabditis elegans, TIR domain proteins are implicated in both development and immunity. Thus, the dual role of the TIR domain is conserved across kingdoms.