Abstract
BackgroundThe genetics of spikelet formation, a feature unique to grasses such as rice and maize, is yet to be fully understood, although a number of meristem and organ identity mutants have been isolated and investigated in Arabidopsis and maize. Using a two-element Ac/Ds transposon tagging system we have isolated a rice mutant, designated branched floretless 1 (bfl1) which is defective in the transition from spikelet meristem to floret meristem.ResultsThe bfl1 mutant shows normal differentiation of the primary rachis-branches leading to initial spikelet meristem (bract-like structure equivalent to rudimentary glumes) formation but fails to develop empty glumes and florets. Instead, axillary meristems in the bract-like structure produce sequential alternate branching, thus resulting in a coral shaped morphology of the branches in the developing panicle. The bfl1 mutant harbours a single Ds insertion in the upstream region of the BFL1 gene on chromosome 7 corresponding to PAC clone P0625E02 (GenBank Acc No. message URL http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=nucleotide&list_uids=34395191&dopt=GenBank&term=ap004570AP004570). RT-PCR analyses revealed a drastic reduction of BFL1 transcript levels in the bfl1 mutant compared to that in the wild-type. In each of the normal panicle-bearing progeny plants, from occasional revertant seeds of the vegetatively-propagated mutant plant, Ds was shown to be excised from the bfl1 locus. BFL1 contains an EREBP/AP2 domain and is most likely an ortholog of the maize transcription factor gene BRANCHED SILKLESS1 (BD1).Conclusionsbfl1 is a Ds-tagged rice mutant defective in the transition from spikelet meristem (SM) to floret meristem (FM). BFL1 is most probably a rice ortholog of the maize ERF (EREBP/AP2) transcription factor gene BD1. Based on the similarities in mutant phenotypes bfl1 is likely to be an allele of the previously reported frizzy panicle locus.
Highlights
The genetics of spikelet formation, a feature unique to grasses such as rice and maize, is yet to be fully understood, a number of meristem and organ identity mutants have been isolated and investigated in Arabidopsis and maize
The large number of genes involved in this complex process can be classified into three categories, namely flowering time genes, meristem identity genes and organ identity genes [18]
Results bfl1 is a mutant defective in the transition from spikelet meristem (SM) to floret meristem (FM) Out of 20 progeny of a mutagenic plant B2-8A-2-18 (F2 generation) derived from a cross between iAc and DsG transgenic lines [31], we found a mutant plant (B2-8A-218-16) with panicle characteristics similar to a previously reported EMS-induced frizzy panicle mutant fzp [20] and a γ-ray induced frizzy panicle mutant fzp2 [15]
Summary
The genetics of spikelet formation, a feature unique to grasses such as rice and maize, is yet to be fully understood, a number of meristem and organ identity mutants have been isolated and investigated in Arabidopsis and maize. Many mutations that affect flowering time have been described in Arabidopsis [3,6,18,27] and some in rice [12,38]. Once this transition is achieved, the inflorescence meristem (IM) produces intermediate meristems that give rise to floret meristems (FMs) to produce floral organs [21]
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