Characterization of the Wheat Ortholog of Br2, an Auxin Transport Regulator of Maize

More than 95% of the world grown wheat crop contains same rht dwarfing genes, Rht1 or Rht2. This genetic uniformity may become a bottleneck for further improvement of the wheat plant if any negative effects are associated with these genes as suggested by some of the recent reports. Therefore, the objective of this study is to develop an alternate dwarfing gene system for wheat. Among various genes reported to reduce plant height, auxin transport regulator gene of maize (br2) is particularly appealing as mutations in its sorghum ortholog (dw3) has been commercially used for decades. Since the mutation in the br2 gene doesn’t affect biosynthesis or signaling of auxin, but favorably change its distribution such that less auxin in roots promote root growth and more auxin in the upper parts of the plant may be resulting into bigger inflorescence. Sequence analysis across crop plants showed the Br2 gene to be highly conserved among all plants compared including Arabidopsis (71%), sorghum (91%), rice (85%), and barley (83%) except parts of exon-I and three other small localized regions.  Putative wheat ortholog, represented as five ESTs, of the gene showed an overall sequence similarity of more than 80% at protein level. Mapping of the gene using parts of these ESTs as probes located the gene on the short arm of wheat homoeologous chromosome group 7 with one copy present on each of the three homoeologues. Virus induced gene silencing (VIGS) using three different oligos corresponding to the wheat showed significant reduction of plant height at maturity compared to virus and no-virus controls. The three homoeologs copies of this gene are differentially expressed in different plant parts. Using hairpin RNAi construct, 110 stable transformed plants were produced. Gene integration of these plants will be confirmed by PCR and southern analysis.