Cloning the Tomato Curl3 Gene Highlights the Putative Dual Role of the Leucine-Rich Repeat Receptor Kinase tBRI1/SR160 in Plant Steroid Hormone and Peptide Hormone Signaling

Abstract

Brassinosteroids (BRs) are plant steroid hormones that are essential for normal plant development. To gain better understanding of the conservation of BR signaling, the partially BR-insensitive tomato mutant altered brassinolide sensitivity1 ( abs1 ) was identified and found to be a weak allele at the curl3 ( cu3 ) locus. BR content is increased in both of these mutants and is associated with increased expression of Dwarf . The tomato homolog of the Arabidopsis Brassinosteroid Insensitive1 Leu-rich repeat (LRR) receptor-like kinase, named tBri1 , was isolated using degenerate primers. Sequence analysis of tBRI1 in the mutants cu3 and abs1 revealed that cu3 is a nonsense mutant and that abs1 is a missense mutant. A comparison of BRI1 homolog sequences highlights conserved features of BRI1 sequences, with the LRRs in close proximity to the island domain showing more conservation than N-terminal LRRs. The most homologous sequences were found in the kinase and transmembrane regions. tBRI1 (SR160) also has been isolated as the putative receptor for systemin, a plant peptide hormone. This finding suggests a possible dual role for tBRI1 in steroid hormone and peptide hormone signaling.

The brassinosteroid signal transduction pathway

“…Mutations of BRI1 orthologs in rice, pea, and tomato cause BR insensitive dwarf phenotypes [37][38][39], suggesting highly conserved function of BRI1. Interestingly, the tomato BRI1 was shown to function as receptor for both BR and systemin, a small peptide involved in plant defense (reviewed by Wang and He, 2004 [40]).…”

Molecular identification and characterization of the tomato flagellin receptor LeFLS2, an orthologue of Arabidopsis FLS2 exhibiting characteristically different perception specificities

“…Additional insights into their functions can be provided by comparative analysis of homologous receptors in another species. For example, the tomato RLK SR160 has been postulated to exhibit dual functionality as receptor for brassinosteroid and systemin (Montoya et al 2002).…”

Differential expression of the brassinosteroid receptor-encoding BRI1 gene in Arabidopsis

“…Severe bri1 mutants lacking functional BR receptors show serious developmental defects, such as severe dwarfness, irregular vascularization, and male sterility (Clouse et al 1996;Montoya et al 2002), which have also been observed in BR-deficient plants (Szekeres et al 1996;Li et al 1996;Bishop et al 1996). This indicates the essential role of BRI1 in BR perception.…”