Brassinosteroids (BRs) control virtually every aspect of plant growth and development. BRs act alone or with other exogenous and endogenous signals including auxin and light. To screen for the novel player involved in BR signaling in Arabidopsis, we employed cDNA overexpression strategy. We created a cDNA library to be expressed under the 35S overexpression promoter, and introduced into a weak brassinosteroid insensitive 1 (bri1) mutant. The mutant dubbed bri1-5 with long petiole (blp) was identified to display bigger stature especially in hypocotyl and petiole length relative to bri1-5. Sequence analysis of the rescued transgene revealed that blp consisted of a chimeric DNA consisting of a 3’ half of PHYB, 2 bp insertion, and a part of a chloroplast ribosomal RNA. Re-introduction of chimeric DNA into bri1-5 recapitulated blp phenotype. The blp phenotypes being similar to phyB mutants led us to examine both the PHYB transcript and protein levels in the blp 35Spro:PHYB doubly homozygous line. Lower levels of both transcripts and proteins of PHYB suggested that introduction of the chimeric gene interfered with the stability of PHYB transcripts. Our results highlight that overexpression mutagenesis facilitates functional genomics to decipher a function of Arabidopsis genome.

Hormones play a crucial role in controlling physiological processes, and thus plants grow and develop in response to environmental cues through the interlocked actions of the hormones. Brassinosteroids (BRs) were found as growth-promoting steroid hormones. Rice, as a monocotyledonous model plants and the major staple crop, has been used to study BR action mechanisms. However, many components of BR pathways and the mechanisms of their molecular interactions have yet to be fully understood. Because the use of the BR biosynthetic inhibitor, Brassinazole (Brz), allowed us to identify important components of BR signaling such as the transcription factor BZR1, we decided to employ a similar strategy to identify novel signaling factors using propiconazole (Pcz), a new potent BR inhibitor. We screened a rice T-DNA mutant population which belongs to Dongjin variety and were developed by the Gene An’s group using pGA2715 T-DNA vector. Using Pcz treatments we searched for resistant plants, which were reflected on their lengths of roots and/or leaves. We isolated a total of 17 mutant lines, which are being analyzed phenotypically and at molecular level. So far, we have been able to found various lines presenting high or low yield compared to their wild type counterparts. We have found differences in panicle organization of these mutants. Our current experiments include the confirmation of Pcz resistance of these lines and molecular studies involving BR marker genes to understand the relation among yield and BR action in rice.