Is kinase activity essential for biological functions of BRI1?

Abstract

npg Brassinosteroids (BRs) are a major group of plant hormones that regulate plant growth and development. BRI1, a protein localized to the plasma membrane, functions as a BR receptor and it has been proposed that its kinase activity has an essential role in BR-regulated plant growth and development. Here we report the isolation and molecular characterization of a new allele of bri1, bri1-301, which shows moderate morphological phenotypes and a reduced response to BRs under normal growth conditions. Sequence analysis identified a two-base alteration from GG to AT, resulting in a conversion of 989G to 989I in the BRI1 kinase domain. An in vitro assay of kinase activity showed that bri1-301 has no detectable autophosphorylation activity or phosphorylation activity towards the BRI1 substrates TTL and BAK1. Furthermore, our results suggest that bri1-301, even with extremely impaired kinase activity, still retains partial function in regulating plant growth and development, which raises the question of whether BRI1 kinase activity is essential for BR-mediated growth and development in higher plants.

Teaching an Old Hormone New Tricks: Cytosolic Ca2+ Elevation Involvement in Plant Brassinosteroid Signal Transduction Cascades

“…Mutations that result in a "kinase-dead" BRI1 impair BR signaling, but binding of the hormone to the receptor is not necessarily impacted by such mutations . The bri1-301 genotype is such a mutant (Xu et al, 2008;Kang et al, 2010). In contrast to the dnd1 mutant, which showed no BR-dependent increase in IAA1 expression, the effect of BR addition on IAA1 expression in these two mutant genotypes is similar to the wild type (Fig.…”

Specific ER quality control components required for biogenesis of the plant innate immune receptor EFR

“…Mutations in ER-QC components have been reported to specifically suppress the phenotype of the weak Arabidopsis bri1-9 and bri1-5 alleles by relaxing ER-QC, so that partially misfolded, but yet functional proteins can escape the ER and reach the plasma membrane (30,45). We examined suppression of bri1-9 in crt3-1 mutants and found that like UGGT mutations (30), crt3-1 specifically suppresses the phenotype of bri1-9 but not bri1-301 that carries a mutation in the kinase domain (46) (Fig. S8).…”

Brassinosteroids Are Master Regulators of Gibberellin Biosynthesis in Arabidopsis

“…Since cold treatment of imbibed seeds (stratification) is known to induce GA biosynthesis and thereby facilitate germination (Yamauchi et al, 2004;Penfield et al, 2005;FinchSavage et al, 2007), we first investigated if stratification can promote germination of BR mutant seeds. For this analysis, we picked bri1-301 since it is less compromised in seed production than bri1-1 (Xu et al, 2008). Four days of stratification fully restored germination of bri1-301 seeds ( Figure 1B), indicating that BRs act upstream of cold on GA biosynthesis in seeds.…”

“…We harvested seeds of plants homozygous for cpd, bri1-1, and bri1-301, a second bri1 null allele in the Col-0 background with milder phenotypes than bri1-1 (Xu et al, 2008), and plated them on water-agar. The seeds were directly incubated in the light at 21°C (without a cold treatment) and germination was assessed after 6 d of incubation.…”