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Summary: The branched silkless1 (bd1) reference mutant was first described by Kempton in 1934. In strong alleles the spikelet meristems of the ear are replaced by long branches that morphologically resemble those seen in the tassel. In addition, no florets are initiated in the ear. In the tassel, the phenotype is less severe, possibly due to expression of the duplicate of bd1. While the spikelets of tassels are still indeterminate and branch-like, florets are initiated that produce viable pollen. The bd1 gene was cloned by transposon tagging with a Mu1 element and found to encode an ERF-like APETALA2 transcription factor. A similar mutant in rice called frizzy panicle was later cloned and found to be orthologous to bd1. Phylogenetic analysis of the bd1 gene demonstrated high conservation of the gene in all grass lineages with spikelets, indicating that the gene may be fundamental to spikelet initiation.
Images: bd1-N ear next to a wild type sibling
First and defining reports: Kempton (1934); Chuck et al. 2002.
Key Alleles
All mutant alleles are female sterile and male fertile:
bd1-reference, ear silkless with indeterminate branches at base; tassel proliferated; insertion of proline amino acid in 5' end. Note, the bd1-refence stock available at Maize Genetics Cooperation Stock Center is probably a double mutant with papyrescent glume1.
bd1-N2355, EMS allele with stop codon.
bd1-RescueMu, 3' end deletion.
bd1-glumy, frameshift mutation resulting in premature stop.
Map Location
Linked to various chromosome 7 breakpoints (see MaizeGDB); between bnl5.6a and bnl8.21a (Chuck et al. 2002).
Expression
bd1 is specifically expressed at the base of the initiating spikelet meristem next to the glumes in both the tassel and ear. Faint expression persists at the base of the florets.
References
Kempton, JH. (1934) HERITABLE CHARACTERS IN MAIZE: XLVII. Branched Silkless . J Heredity 25:29-32.
Chuck G, Muszynski M, Kellogg E, Hake S, Schmidt RJ (2002). The control of spikelet meristem identity by the branched silkless1 gene in maize. Science 298:1238-1241. PUBMED
Links: MGDB: bd1 NCBI bd1 UniProt Q84J59