Inflorescences of grass species have a distinct morphology in which florets are grouped in compact branches called spikelets. Although many studies have shown that the molecular and genetic mechanisms that control floret organ formation are conserved between monocots and dicots, little is known about the genetic pathway leading to spikelet formation. In the frizzy panicle (fzp) mutant of rice, the formation of florets is replaced by sequential rounds of branching. Detailed analyses revealed that several rudimentary glumes are formed in each ectopic branch, indicating that meristems acquire spikelet identity. However, instead of proceeding to floret formation, axillary meristems are formed in the axils of rudimentary glumes and they either arrest or develop into branches of higher order. The fzp mutant phenotype suggests that FZP is required to prevent the formation of axillary meristems within the spikelet meristem and permit the subsequent establishment of floral meristem identity. The FZP gene was isolated by transposon tagging. FZP encodes an ERF transcription factor and is the rice ortholog of the maize BD1 gene. Consistent with observations from phenotypic analyses, FZP expression was found to be restricted to the time of rudimentary glumes differentiation in a half-ring domain at the base of which the rudimentary glume primordium emerged.
禾本科植物的花序有個(gè)明顯的形態(tài)特征，即小花成簇著生于稱之為小穗的緊密枝梗上。雖然有許多研究發(fā)現(xiàn)小花器官形成的分子遺傳機(jī)制在單、雙子葉植物中是保守的，但小穗形成的遺傳路徑仍然知之甚少。在水稻卷穗突變體中，小花的形成被有序的枝梗取代。詳細(xì)的分析揭示在每個(gè)異位枝梗上長(zhǎng)有多個(gè)退化的穎苞，暗示分生組織獲得了小穗身份。然而，取代小花的形成進(jìn)程，葉腋分生組織在退化穎苞的處形成，它們要么終止發(fā)育要么發(fā)育成更高形式的枝梗。fzp 突變體表型暗示FZP 對(duì)阻止小穗分生組織中的葉腋分生組織的形成，以及允許隨后的花分生組織身份的有序建立是必須的。FZP 基因通過(guò)轉(zhuǎn)座子標(biāo)記技術(shù)成功分離。FZP 編碼一個(gè)ERF 轉(zhuǎn)錄因子，是玉米BD1 在水稻中的同源基因。與表型觀察分析一致，FZP 表達(dá)限制在退化穎苞分化的時(shí)期，部位在退化穎殼原基基部的半環(huán)域。