Brassinosteroid-Insensitive Dwarf Mutants of Arabidopsis Accumulate Brassinosteroids

Abstract

Seven dwarf mutants resembling brassinosteroid (BR)-biosynthetic dwarfs were isolated that did not respond significantly to the application of exogenous BRs. Genetic and molecular analyses revealed that these were novel alleles of BRI1 (BrassinosteroidInsensitive 1), which encodes a receptor kinase that may act as a receptor for BRs or be involved in downstream signaling. The results of morphological and molecular analyses indicated that these represent a range of alleles from weak to null. The endogenous BRs were examined from 5-week-old plants of a null allele (bri1-4) and two weak alleles (bri1-5 and bri1-6). Previous analysis of endogenous BRs in several BR-biosynthetic dwarf mutants revealed that active BRs are deficient in these mutants. However, bri1-4 plants accumulated very high levels of brassinolide, castasterone, and typhasterol (57-, 128-, and 33-fold higher, respectively, than those of wild-type plants). Weaker alleles (bri1-5 and bri1-6) also accumulated considerable levels of brassinolide, castasterone, and typhasterol, but less than the null allele (bri1-4). The levels of 6-deoxoBRs in bri1 mutants were comparable to that of wild type. The accumulation of biologically active BRs may result from the inability to utilize these active BRs, the inability to regulate BR biosynthesis in bri1 mutants, or both. Therefore, BRI1 is required for the homeostasis of endogenous BR levels.Based on their wide distribution in the plant kingdom, their diverse physiological effects at nanomolar levels, and the discovery of mutants deficient in their biosynthesis, it is now widely accepted that brassinosteroids (BRs) are important hormones that regulate growth and development

Receptor serine/threonine protein kinases in signalling: analysis of the erecta receptor‐like kinase of Arabidopsis thaliana

“…Sequence analysis of bri1 alleles provides additional evidence for the importance of the extracellular LRR domain and the cytoplasmic protein kinase domain ( Li & Chory, 1997;Noguchi et al , 1999;Friedrichsen et al , 2000). Mutations that result in strong phenotypes occur in both the protein kinase domain and the extracellular LRR domain, including the 70 amino acid island ( Noguchi et al , 1999).…”

“…Mutations that result in strong phenotypes occur in both the protein kinase domain and the extracellular LRR domain, including the 70 amino acid island ( Noguchi et al , 1999).…”

Specialized Roles of the Conserved Subunit OST3/6 of the Oligosaccharyltransferase Complex in Innate Immunity and Tolerance to Abiotic Stresses

“…The mutants alg10-1, alg10-1 gntI, alg10 cgl1 (Farid et al, 2011), gntI (Kang et al, 2008), stt3a-2 (Koiwa et al, 2003), cgl1 (von Schaewen et al, 1993, efr-1 (Zipfel et al, 2006), fls2c efr-1 ), rsw2-1 (Lane et al, 2001), bri1-9, and bri1-5 (Noguchi et al, 1999) are all available from previous studies (Zipfel et al, 2006;Liebminger et al, 2009;Farid et al, 2011;Hüttner et al, 2012). Tunicamycin, ABA, and other chemicals for seedling germination and growth assays were purchased from Sigma-Aldrich.…”

“…To investigate whether proper OST3/6 function is required for the biogenesis or functionality of mutant variants of the LRR-RK BRI1 (Li and Chory, 1997), we crossed ost3/6-1 to the weak bri1 alleles bri1-9 and bri1-5 and analyzed the suppression or enhancement of the bri1-9 or bri1-5 dwarf phenotype (Noguchi et al, 1999). The bri1-9 and bri1-5 plants contain mutant alleles of the BRI1 gene and express structurally altered but still functional BRI1 proteins that are retained in the ER by different quality control processes, including glycan-dependent mechanisms (Jin et al, 2007;Hong et al, 2008Hong et al, , 2012.…”

Two Putative BIN2 Substrates Are Nuclear Components of Brassinosteroid Signaling

“…It was well documented that gene regulation is critical for many BR-elicited physiological responses (Clouse and Feldmann, 1999), however, the signaling mechanism from BR perception to gene regulation remains largely unknown. Extensive genetic screens for BR-insensitive-signaling mutants in Arabidopsis have so far identified only two genes, BRI1 and BIN2 (Clouse et al, 1996;Kauschmann et al, 1996;Li and Chory, 1997;Noguchi et al, 1999;Li et al, 2001;Li and Nam, 2002).BRI1 encodes a Leu-rich repeat receptor-like kinase that is composed of an extracellular domain, a singlepass transmembrane segment, and an intracellular kinase domain (Li and Chory, 1997). BRI1 is a plasma membrane-localized protein and can function as a Ser/Thr kinase when expressed in Escherichia coli or animal cell culture (Friedrichsen et al, 2000;Oh et al, 2000).…”