Comparative Analysis and Characterization of the Brassinosteroid Receptor Protein Gene, BRI1, in Wheat

Brassinosteroids (BRs) are fundamental plant hormones involved in the growth and development of wide variety of plants. A trans-membrane protein receptor kinase, Brassinosteroid Insensitive 1 (BRI1) is known to interact with BRs and is directly involved in plant development. The BRI1 loss of function mutant showed significant reduction in height in Arabidopsis without affecting fertility, making it an ideal candidate for manipulating height in wheat. The Bri1 gene is well characterized in Arabidopsis but largely unknown in wheat and other crop plants. A cross-species sequence analysis of BRI1 suggested that the gene in Triticum aestivum (TaBRI1) shows 54%, 95%, 83% and 79% identity at amino acid level to Arabidopsis (AtBRI1), Barley (HvBRI1), rice (OsBRI1) and maize  BRI1 (ZmBRI1), respectively.  Comparison of BRI1 sequences from several plant species revealed distinct variation in the number of leucine rich repeats between monocots and dicots. Expression studies using tissues from root, lower stem, upper stem, leaf sheath, leaf, and ear suggested that the highest gene expression was observed in the stem and lowest in the leaf. Virus-Induced Gene Silencing (VIGS) was conducted using barley stripe mosaic virus (BSMV) containing two non-conserved region specific Bri1constructs. VIGS analyses with two different antisense constructs for TaBri1showed induction of dwarfing in the inoculated plants compared to the viral (photoene desaturase and MCS) and non-viral inoculated plants. Transient silencing of TaBri1 suggested that it is true ortholog of AtBri1 and is a good candidate for inducing dwarfing in wheat.