Abstract
FRIZZLE PANICLE (FZP) and RFL/ABERRANT PANICLE ORGANIZATION 2 (APO2) play important roles in regulating the ABCDE floral organ identity genes. However, the relationships among FZP and these floral identity genes in the regulation of panicle formation remain unclear. Here, we used the novel mutant fzp-11, wild-type and FZP-overexpressing plants to compare the expression of these genes during panicle development by real-time PCR and in situ hybridization. The results indicate that FZP is a major negative regulator of RFL/APO2 and determines the transition from panicle branching to spikelet formation. Moreover, overexpression of FZP severely represses axillary meristem formation in both the vegetative and reproductive phases and the outgrowth of secondary branches in panicle. FZP overexpression positively regulates the expression of a subset of the class B genes, AGL6 genes (OsMADS6 and OsMADS17) as well as class E genes (OsMADS1, OsMADS7 and OsMADS8) in floral meristem (FM). Thus, it suggested that FZP could specify floral organ identity by regulating the related OsMADS-box genes.
Highlights
Rice is an important model that is used to study plant growth and development
The panicle morphology of fzp-11 was significantly different from that of wild-type DJ, with numerous panicle branches, including higher order tertiary and quaternary branches that replaced the normal spikelets in primary and secondary branches, whereas they were normally not produced in wild-type DJ plants (Fig. 1C and Table 1)
We found that the downregulation of class B and C genes accompanied with abortion of spikelet formation in fzp-11 plants; the expression of FRIZZY PANICLE (FZP) was initiated before the expression of class B and C genes
Summary
Rice is an important model that is used to study plant growth and development. Panicle formation, including panicle branching and spikelet formation, is an integral process in rice development that determines grain yield. The panicles of lax[1] spa double mutants are wire-like structures with no branches[8] In addition to these genes, two quantitative trait loci (QTLs), DENSE and ERECT PANICLE 1 (DEP1) and GRAIN NUMBER 1a (GN1a), control panicle branching. Fewer stamens and enlarged carpels were observed in the flowers of OX-FZP plants. FZP, RFL/APO2 and OsMADS-box genes play important roles in FM determination and normal spikelet formation, the regulatory relationships involved remain poorly understood. We compared the expression of genes controlling panicle architecture and floral organs in plants of overexpressing FZP, wild-type (Dongjin, DJ) and the new mutant fzp-11, and we concluded that FZP regulates panicle branching and spikelet formation by regulating RFL/APO2 and FZP overexpression elevated the expression of some floral identify genes
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