Abstract:  Shoot architecture is a key determinant of grain yield in maize. Among the major plant growth regulators, brassinosteroids (BRs) affect multiple developmental processes and plant architecture traits, including organ size, sex determination, and leaf angle. However, the genetic mechanisms by which BRs regulate plant architecture traits in maize remain poorly understood. We recently generated, identified, and characterized a recessive, EMS-induced maize mutant, which we tentatively named brassinosteroid deficient semi-dwarf mutant1 (bds1). Mutants have a semi dwarf stature due to compressed internodes and are partially rescued by brassinolide. bds1-ref mutants also have short leaf sheaths and twisted leaf blades and display a partial tassel-seed phenotype in the Mo17 background and reduced tassel branch number in B73. We localized bds1 to a small genomic region containing a point-nonsense mutation in a gene involved in brassinosteroid biosynthesis using map-based cloning and whole-genome sequencing. Non-complementation of bds1-ref and a bds1-Mu allele confirmed that bds1 encodes an enzyme likely involved in brassinosteroid biosynthesis. Using phylogenetic and blast analysis, we identified that bds1 has a close homolog. We named bds2 and generated several mutant alleles by remobilizing a nearby Ds transposable element. 

Contrary to bds1 mutants, the bds2 single mutants are indistinguishable from wild-type plants, while the bds1-ref;bds2-Ds double mutants are severely dwarfed with other defects similar to those observed with BR-deficient mutants nana1 and nana2. To understand the genetic interaction between brassinosteroids and Jasmonic Acid, generated double-mutants between bds1-R with tassel-seed 1 (ts1) mutant. We observed synergistic interaction between bds1-R and ts2, the bds1-R;ts2 double mutants have dramatically increased tassel feminization and reduced plant height and tassel branches. Suggesting that both BR and JA biosynthesis are required for sex determination and plant architecture regulation.  

Metabolite accumulation profiling analysis and feeding experiments are ongoing to confirm and characterize how the bds1 and bds2 mutants disrupt brassinosteroid biosynthesis. Based on these results, we propose that bds1 and bds2 cooperatively regulate shoot architecture and brassinosteroid biosynthesis.  

The Bio-WIP Seminars (formerly BBMB WIP seminars) are sponsored by the BBMB Graduate Learning Community. All are welcome to join!