The LKA gene is a BRASSINOSTEROID INSENSITIVE 1 homolog of pea

Abstract

SummaryBrassinosteroids (BRs) are growth-promoting plant steroid hormones, and in garden pea (Pisum sativum L.), the lka mutant is defective in BR perception. Here, we show that LKA encodes P. sativum BRI1 (PsBRI1), a homolog of BRI1, which is the Arabidopsis leucine-rich repeat receptor-like kinase/BR receptor. PsBRI1 was isolated by screening a pea cDNA library using Arabidopsis BRI1 cDNA as the probe. PsBRI1 is predicted to encode a 1188-amino-acid protein that has 78% similarity with Arabidopsis BRI1. Sequence analysis of PsBRI1 in the lka mutant led to the identi®cation of a missense mutation that converts the highly conserved aspartic acid residue to asparagine, which is located in the leucine-rich repeat, just before the island domain that may bind BR or a BR±protein complex. The mutation identi®ed in PsBRI1 co-segregated with the semi-erectoide lka phenotype. Transcript analysis of LKA/PsBRI1 indicates that it is ubiquitously expressed in pea and that the expression was downregulated by exogenous BR. The lka mutant was then utilized in further studies to analyze the independent actions of BR and gibberellin (GA) through the characterization of BR response on GA mutants and GA response on BR mutants.

Brassinosteroids Do Not Undergo Long-Distance Transport in Pea. Implications for the Regulation of Endogenous Brassinosteroid Levels

“…As was the case in previous studies in pea Symons and Reid, 2003a) and Arabidopsis , BL levels were below detection limits in all of the tissue types studied (Tables I and III Comparative Distribution of BRs in Wild-Type, lka, and lkb Plants Nomura et al (1999) have previously reported that BR levels are elevated in whole shoots of lka mutant plants and reduced in whole shoots of lkb mutant plants, in comparison with the wild type. This is consistent with the finding that the lkb mutation blocks the biosynthesis of BRs, while the lka mutation causes impaired perception of these substances (Nomura et al, , 2003Schultz et al, 2001). In this study, we show that these changes in endogenous BRs in lka and lkb mutant plants (compared to the wild type) are consistent across a wide range of different shoot tissues and are not restricted to any specific location (Table III).…”

“…In contrast, it has previously been reported that 100 ng of BL in 10 mL of ethanol, applied to the third leaf (including leaflets, stipules, and petioles) of various pea genotypes, results in increased growth of the fourth internode (Nomura et al, 1997(Nomura et al, , 2003, thus implying some movement of exogenous BRs from the leaf to the stem. However, due to the relatively large volume of ethanol used, we cannot exclude the possibility that the increase in growth came about because some of the applied BL came into contact with the surface of the fourth internode itself.…”

Grapes on Steroids. Brassinosteroids Are Involved in Grape Berry Ripening

“…This fragment, from the 3# part of the gene, contained an open reading frame of 401 amino acids and was 91.3% identical (at the amino acid level) to the BRI homolog from pea (accession no. AB104529; Nomura et al, 2003). This gene was therefore assigned as a putative grape BRI1 homolog (VvBRI1).…”

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]).…”