BIANNUALREPORT2012-2013

Different functional steroid hormone receptor complexes exist for specific cell types in plants

Plant steroids are called brassinosteroids (BRs) since they were discovered in the pollen of the plant Brassica napus. BRs are essential hormones that regulate plant growth and development, and they are able to regulate a myriad of biological processes such as cell elongation, cell division, cell differentiation, pollen viability, germination and flowering time, among others.

Despite the resemblance of BRs to animal steroids, which are perceived in the nucleus, plant steroid receptors are located at plasma cell membrane. BRI1 (BR insensitive 1) is the main BR receptor that binds the hormone and it is expressed within most cells of the root meristem (image, left). Additionally to BRI1, plants express other BR receptors, called BRL1 (BRI1-like 1) and BRL3 (BRI1-like 3), which specifically localize within the stem cells of the root meristem (image, right).

The group led by CSIC investigator Ana Caño-Delgado identified the BRL3 signalosome complex in planta and characterized its contribution to plant development. Immunoprecipitation and liquid chromatography followed by mass spectrometry of BRL3 receptors identify BRL1 and BAK1 (BRI1 associated kinase 1) proteins as part of the BRL3 signalosome.

The study has uncovered a novel role for the BRL3 signalosome complex in regulating cell division within the Arabidopsis primary root meristem. On one hand, the BRL3 complex promotes root length and division of the root stem cells (specifically, quiescent centre cells which normally display low-rate division) independently from the BRI1 receptor. On the other, the BRL3 complex regulates provascular stem cell division in a distinct manner than BRI1, which suggest that different BR complexes accomplish cell-type specialized functions.