Abstract
Specification of floral organ identity is critical for the establishment of floral morphology and inflorescence architecture. Although multiple genes are involved in the regulation of floral organogenesis, our understanding of the underlying regulating network is still fragmentary. MADs-box genes are principle members in the ABCDE model that characterized floral organs. OsMADS1 specifies the determinacy of spikelet meristem and lemma/palea identity in rice. However, the pathway through which OsMADS1 regulates floral organs remains elusive; here, we identified the microRNA172 (miR172) family as possible regulators downstream of OsMADS1. Genetic study revealed that overexpression of each miR172 gene resulted in elongated lemma/palea and indeterminacy of the floret, which resemble the phenotype of osmads1 mutant. On the contrary, overexpression of each target APETALA2 (AP2) genes resulted in shortened palea/lemma. Expression level and specificity of miR172 was greatly influenced by OsMADS1, as revealed by Northern blot analysis and In situ hybridization. Genetically, AP2-3 and AP2-2 over expression rescued the elongation and inconsistent development of the lemma/palea in OsMADS1RNAi transgenic plants. Our results suggested that in rice, OsMADS1 and miR172s/AP2s formed a regulatory network involved in floral organ development, particularly the elongation of the lemma and the palea.
Highlights
Specification of floral meristem fate and floral organ identity is pivotal for the reproductive development of plants, molecular, and genetic studies led to the establishment of the classic ABC and the modified ABCDE model to explain the development of floral organs (Coen and Meyerowitz, 1991; Angenent et al, 1995; Pelaz et al, 2000; Ditta et al, 2004)
Overexpression of AP2-3 and AP2-2 partially rescued the phenotype of OsMADS1RNAi. These results strongly suggested that miR172/AP2s regulated palea/lemma development and floral determinacy in rice, and OsMADS1 was an upstream suppressor of miR172
According to the severity of the phenotype, the transgenic plants from different miR172s overexpression could be grouped into two classes: miR172aOE, miR712cOE, and miR172dOE were similar and showed severely abnormal floral organs (Figure 1A as compared with Figure 1B), they were tentatively represented as miR172aOEs unless specified; whereas phenotypic abnormality of miR172bOE was moderate
Summary
Specification of floral meristem fate and floral organ identity is pivotal for the reproductive development of plants, molecular, and genetic studies led to the establishment of the classic ABC and the modified ABCDE model to explain the development of floral organs (Coen and Meyerowitz, 1991; Angenent et al, 1995; Pelaz et al, 2000; Ditta et al, 2004). MADs-box genes are characterized by the presence of an approximately 60 amino acids DNA-binding MADS-box domain in the N-terminal (Schwarz-Sommer et al, 1990; Theissen et al, 2000; Arora et al, 2007). Rice belongs to the grass family of monocots, the florets of which contain carpels and stamens, but lack petals and sepals, instead, lodicules surround the sex organs and the lemma/palea envelop the inner floral organs. MADs-box genes, Interaction of miR172 and OsMADS1 such as OsMADS1, OsMADS3 and OsMADS58 (Yamaguchi et al, 2006), OsMADS6 (Ohmori et al, 2009; Li et al, 2010), OsMADS7 and OsMADS8 (Cui et al, 2010), and OsMADS15 (Wang K. et al, 2010) characterize floral organ identities in rice
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