The control of floral organ identity by homeotic MADS box genes is well established in eudicots. However, grasses have highly specialized outer floral organs, and the identities of the genes that regulate the highly specialized outer floral organs of grasses remain unclear. In this study, we characterized a MIKC-type MADS box gene, CHIMERIC FLORAL ORGANS (CFO1), which plays a key role in the regulation of floral organ identity in rice (Oryza sativa). The cfo1 mutant displayed defective marginal regions of the palea, chimeric floral organs, and ectopic floral organs. Map-based cloning demonstrated that CFO1 encoded the OsMADS32 protein. Phylogenetic analysis revealed that CFO1/OsMADS32 belonged to a monocot-specific clade in the MIKCtype MADS box gene family. The expression domains of CFO1 were mainly restricted to the marginal region of the palea and inner floral organs. The floral organ identity gene DROOPING LEAF (DL) was expressed ectopically in all defective organs of cfo1 flowers. Double mutant analysis revealed that loss of DL function mitigated some of the defects of floral organs in cfo1 flowers. We propose that the CFO1 gene plays a pivotal role in maintaining floral organ identity through negative regulation of DL expression.Most flowers consist of four distinct organ types arranged in concentric whorls: sepals (whorl 1), petals (whorl 2), stamens (whorl 3), and carpels and ovules (whorl 4). The well-established ABCDE model, which is mainly based on genetic and molecular studies involving eudicots, such as Arabidopsis (Arabidopsis thaliana), snapdragon (Antirrhinum majus), and petunia (Petunia hybrida), explains how floral organ identity is coordinately defined by A-, B-, C-, D-, and E-class

SummaryAs an important agronomic trait, leaf rolling in rice (Oryza sativa L.) has attracted much attention from plant biologists and breeders. Moderate leaf rolling increases the amount of photosynthesis in cultivars and hence raises grain yield. Here, we describe the map-based cloning of the gene RL14, which was found to encode a 2OG-Fe (II) oxygenase of unknown function. rl14 mutant plants had incurved leaves because of the shrinkage of bulliform cells on the adaxial side. In addition, rl14 mutant plants displayed smaller stomatal complexes and decreased transpiration rates, as compared with the wild type. Defective development could be rescued functionally by the expression of wild-type RL14. RL14 was transcribed in sclerenchymatous cells in leaves that remained wrapped inside the sheath. In mature leaves, RL14 accumulated mainly in the mesophyll cells that surround the vasculature. Expression of genes related to secondary cell wall formation was affected in rl14-1 mutants, and cellulose and lignin content were altered in rl14-1 leaves. These results reveal that the RL14 gene affects water transport in leaves by affecting the composition of the secondary cell wall. This change in water transport results in water deficiency, which is the major reason for the abnormal shape of the bulliform cells.

The spikelet is a unique inflorescence structure in grass. The molecular mechanisms behind the development and evolution of the spikelet are far from clear. In this study, a dominant rice mutant, lateral florets 1 (lf1), was characterized. In the lf1 spikelet, lateral floral meristems were promoted unexpectedly and could generally blossom into relatively normal florets. LF1 encoded a class III homeodomain-leucine zipper (HD-ZIP III) protein, and the site of mutation in lf1 was located in a putative miRNA165/166 target sequence. Ectopic expression of both LF1 and the meristem maintenance gene OSH1 was detected in the axil of the sterile lemma primordia of the lf1 spikelet. Furthermore, the promoter of OSH1 could be bound directly by LF1 protein. Collectively, these results indicate that the mutation of LF1 induces ectopic expression of OSH1, which results in the initiation of lateral meristems to generate lateral florets in the axil of the sterile lemma. This study thus offers strong evidence in support of the "three-florets spikelet" hypothesis in rice.lateral floret | three-florets spikelet | evolution | yield | rice F lower development is a key process in the reproduction of angiosperms. Under suitable conditions, flowering signals are transmitted to shoot apical meristems (SAMs), which are transformed first into inflorescence meristems (IMs). Floral meristems (FMs) are then initiated on the top and/or lateral domains of the IMs and subsequently transformed into the four whorls of floral organs. The spikelet is a unique unit of inflorescence architecture in grasses and consists of a pair of glumes and a fixed or variable number of florets. Some grassspecific genes are involved in regulating spikelet development. For example, FRIZZY PANICLE (FZP) functions in regulating spikelet meristem (SM) identity in rice. In the fzp mutant, axillary meristems (AMs) are formed instead of FMs, and these then develop into higher-order branches (1). Three genes that encode members of the AP2/ERF superfamily, SUPERNUMERARY BRACT (SNB), INDETERMINATE SPIKELET 1 (OsIDS1), and MULTI-FLORETS SPIKELET 1 (MFS1), are involved in regulating spikelet determinacy in rice (2, 3). In these mutants, the transition from SM to FM is delayed, and extra organs or florets are produced. However, our knowledge about the details of spikelet development in rice remains limited.In most members of Oryzeae, the spikelet is composed of one pair of rudimentary glumes, one pair of sterile lemmas, and one terminal fertile floret, which consists of one pair of hulls (lemma and palea) and inner floral organs (4). Regarding the origin of the sterile lemmas, the "three-florets spikelet" hypothesis proposes that the putative ancestor of the rice spikelet contained two lateral florets in addition to a terminal fertile floret. Subsequently, the lemmas of the two lateral florets degenerated into sterile lemmas, and the inner floral organs and palea degenerated markedly and disappeared during evolution (5). In recent years, several reports have supported this hypot...