Abstract
BackgroundThe rice gene, OsMADS45, which belongs to the MADS-box E class gene, participates in the regulation of floral development. Previous studies have revealed that ectopic expression of OsMADS45 induces early flowering and influences reduced plant height under short-day (SD) conditions. However, the regulation mechanism of OsMADS45 overexpression remains unknown. We introduce an OsMADS45 overexpression construct Ubi:OsMADS45 into TNG67 plants (an Hd1 (Heading date 1) and Ehd1 (Early heading date 1) defective rice cultivar grown in Taiwan), and we analyzed the expression patterns of various floral regulators to understand the regulation pathways affected by OsMADS45 expression.ResultsThe transgenic rice exhibit a heading date approximately 40 days earlier than that observed in TNG67 plants, and transgenic rice display small plant size and low grain yield. OsMADS45 overexpression did not alter the oscillating rhythm of the examined floral regulatory genes but advanced (by approximately 20 days) the up-regulate of two florigens, Hd3a (Heading Date 3a) and RFT1 (RICE FLOWERING LOCUS T1) and suppressed the expression of Hd1 at the juvenile stage. The expression levels of OsMADS14 and OsMADS18, which are two well-known reproductive phase transition markers, were also increased at early developmental stages and are believed to be the major regulators responsible for early flowering in OsMADS45-overexpressing transgenic rice. OsMADS45 overexpression did not influence other floral regulator genes upstream of Hd1 and Ehd1, such as OsGI (OsGIGANTEA), Ehd2/Osld1/RID1 and OsMADS50.ConclusionThese results indicate that in transgenic rice, OsMADS45 overexpressing ectopically activates the upstream genes Hd3a and RFT1 at early development stage and up-regulates the expression of OsMADS14 and OsMADS18, which induces early flowering.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-12) contains supplementary material, which is available to authorized users.
Highlights
The rice gene, OsMADS45, which belongs to the MADS-box E class gene, participates in the regulation of floral development
Ectopic expression of OsMADS45 causes early flowering in the TNG67 rice variety To analyze the early flowering enhancing mechanism of OsMADS45 and to demonstrate the probable effects of OsMADS45 in regulating the flowering time when it was overexpressed, we ectopically overexpressed OsMADS45 in the rice variety, TNG67, by transforming the Ubi: OsMADS45 construct containing the OsMADS45 gene driven by the maize ubiquitin promoter (Figure 1A) into the plant
The results showed the expression patterns of the RFT1, Hd3a, Hd1, OsMADS14 and OsMADS18 genes in the 45OX transgenic rice varied from those observed with the TNG67 rice (Figure 3A), thereby suggesting that these genes may be involved in the process of early flowering in the 45OX transgenic rice
Summary
The rice gene, OsMADS45, which belongs to the MADS-box E class gene, participates in the regulation of floral development. The plant developmental transition from vegetative to reproductive growth is regulated by multiple genes and environmental factors, such as temperature and photoperiod (Koornneef et al 1998; Wilczek et al 2010). In rice, this transition influences the time of floral heading. Hd3a and RFT1 translocate from the leaf to the apical meristem, thereby activating the expression of downstream genes, such as OsMADS14, OsMADS15 and OsMADS18, which regulate flower development (Tamaki et al 2007; Komiya et al 2008; Komiya et al 2009; Kobayashi et al 2012)
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