Abstract
Brassinosteroids (BRs) are plant hormones, fundamental for the growth and development of plants. A trans-membrane protein receptor kinase, Brassinosteroid-Insensitive 1 (BRI1), is known to interact with BRs and be directly involved in plant development. This study investigates the structural organization of BRI1 orthologs in several taxa, with a specific interest in Triticum aestivum. True orthologs of Arabidopsis thaliana BRI1 (AtBRI1) from seven-plant species showed sequence identity ranging from 54% to 95% at the protein level. All gene sequences lacked introns, leading to speculation that post-transcriptional processing in TaBRI1 is similar to AtBRI1. Based on in silico analysis, a single copy of BRI1 was present in each of the three wheat genomes on the long arm of chromosome 3. Domain structure of BRI1 orthologs among different taxa showed multiple leucine rich repeats (LRRs), an island domain (ID), a juxtamembrane/transmembrane domain (JTMD), a catalytic kinase domain (KD), C and N-Terminal domains. The KD showed the highest level of conservation while the LRRs and JTMD were most variable. Phosphorylation of residues in the juxtamembrane domain, known to be involved in the activation of the KD, is conserved in TaBRI1. While TaBRI1 has well-defined differences in the ID and LRR domains, many residues involved in ligand binding are conserved. The activation loop present in the KD showed 100% conservation in all taxa. Despite residue differences, hydrophobicity was conserved in the BR binding pocket across taxa, suggesting that function may not differ as drastically as residue identity may suggest. Predicted 3D structure of AtBRI1 and TaBRI1 showed a conserved super helical assembly, a feature essential in protein-protein interactions. An unrooted phylogram showed TaBRI1 in the monocot clade to be distinct from that of dicots. New insight in the structure and functions of BRI1 may help in targeting BR pathway for crop improvement.
Highlights
Steroid hormones play important role in the growth and development of living organisms
The conservation seen in the schematic of gene lengths suggests that the relative sizes of Brassinosteroid-Insensitive 1 (BRI1) across species are similar for the two different monocot and dicot groups
The lack of introns in all genes suggests that the mechanism for post-transcriptional processing of BRI1 is similar in both A. thaliana and T. aestivum
Summary
Steroid hormones play important role in the growth and development of living organisms. Brassinosteroids (BRs) are known to be involved in various physiological responses including: cell division, cell differentiation, stem elongation, male fertility, vascular development, flowering, photomorphogenesis and responses to environmental stresses [1,2,3,4]. Signal cascades involving BRI1 regulate developmental processes and are known to modulate the gibberellin pathway as well [7,8,9]. By measuring fluorescence resonance energy transfer between BRI1CFP and BRI1-YFP, it is known that BRI1 exists in the plasma membrane as a homo-oligomer [10]. While many of the components of the BR signaling pathway have been identified and characterized, BRI1 and its mechanisms in crop plants are under-explored
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