Background: The 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.
Results: The 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. AP004570). 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).
Conclusions: bfl1 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.
背景：小穗形成是禾本科植物如水稻和玉米特有的特征，其遺傳機制并不完全清楚，雖然許多擬南芥和玉米的分生組織和器官屬性突變體已經被分離和研究。利用雙組分Ac/Ds轉座子標簽系統(tǒng)，我們分離到了一個小穗分生組織不能向小花分生組織轉變的水稻突變體，并將之命名為branched floretless 1 (bfl1)。
結果：bfl1突變體的一級枝?？梢哉７只鰜恚鹗夹∷敕稚M織（類似苞葉的結構相當于未發(fā)育的漿片）的形成，但不能發(fā)育成空的內外稃和小花，而是位于類似苞葉的結構上側生分生組織連續(xù)產生交替的分枝，從而導致穗上形成珊瑚狀的分枝。bfl1突變體攜帶單個Ds插入，Ds插入7號染色體上對應于PAC克隆P0625E02 (GenBank Acc No.AP004570)的BFL1基因上游。RT-PCR分析表明bfl1突變體中BFL1的表達比野生型顯著降低。從突變體中偶爾分離出穗部正常的后代中，Ds都從bfl1位點上跳出。BFL1基因編碼的蛋白含有EREBP/AP2結構域，很可能是玉米轉錄因子基因BRANCHED SILKLESS1 (BD1)的直系同源基因。
結論：bfl1是一個Ds插入的突變體，小穗分生組織不能轉變成小花分生組織。BFL1很可能是玉米ERF (EREBP/AP2)轉錄因子基因BD1的水稻直系同源基因。根據(jù)表型的相似性，bfl1突變體可能是已報道的frizzy panicle的等位基因突變體。