# The Snapdragon LATE Elongated Hypocotyl
## 1 Introduction  
Floral organs are arranged in whorls of sepals, petals, stamens, and carpels. They acquire their identities when a set of genes called floral organ identity genes are activated. These organ identity genes activate the morphogenetic program in combinations [1]. The MADS-BOX genes DEFICIENS and GLOBOSA form protein complexes that drive petal and stamen development [2; 3]. The so-called C-function genes are involved in the organ identity of the stamens and carpels [4] and cause the termination of the floral meristem development [5; 6].  
Floral organ size is primarily controlled by the organ identity genes in a quantitative way [7; 8]. Changes in floral organ size occur by changes in the time and/or rate of cell division and expansion [9; 10]. Lateral organs grow by a combination of cell division and expansion. Several genes controlling these processes also play a role in the final size of the flower. Amongst them are the transcription factor _AINTEGIMENTA_[1; 2; 3; 4], affecting both cell division and expansion and _EXPANSINS_, which control primarily cell expansion [11; 12].  
The emission of floral scent occurs in many cases from petal tissues [13] and has several functions including the attraction and guidance of pollinators and the repulsion of non-beneficial insects [14; 15]. Apart of the important role of Volatile Organic Compounds (VOCs) emission in plant reproduction and protection, the general floral bouquet, which is perceived by the human olfactory system, is also of aesthetic value [16; 17]. Floral volatiles are emitted in a circadian fashion and this fact characterizes some plants as day emitters, like _Antirhinum_ or roses, or night emitters, like _Petunia_ or _Silene_[18; 19; 20], indicating that the majority of the volatiles are released during a given timeframe.  
The circadian clock has been extensively studied in Arabidopsis [21]. Research on circadian clock in other species is increasingly contributing to the understanding of the genetics of the circadian clock in plants and the importance of its restructuring for optimal outputs in adaptation to the environment [22; 23; 24]. Cell expansion is controlled by the circadian clock through the coordination of DELLA (aspartic acid-glutamic acid-leucine-leucine-alanine) proteins and the PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors [25]. Cell division is also under the direct control of the clock via binding of TIMING OF CAB 1 to the promoter of _CDC6_ in Arabidopsis [26]. Scent emission is also directly controlled by the clock. Knocking down the _LATE ELONGATED HYPOCOPYL_ (_LHY_) in _Petunia_ causes the down regulation of the benzenoid/phenylpropanol pathway [27], limiting the timing of floral volatile emission to the evening. Additional evidence for a direct role of the circadian clock on the regulation of floral scent emission has been found in _Nicotiana attenuate_, where knockdown of _LHY_ or _ZEITLUPE_ cause changes in the emission of the attractant benzyl acetone [28]. Recent work has shown that the ortholog of _ZEITLUPE_ in _Petunia_, _PhCHANEL_, coordinates scent profiles [29].  
In this work, we have addressed the function of the core clock gene _LHY_ on flower development in _Antirhinum majus_ using RNA interference. Using a phenomics approach we analyzed the effect of knocking down _AmLHY_ on growth. We also analyzed in detail the function of _AmLHY_ on scent emission. Our results indicate a non-linear and complex control of the floral scent synthesis and emission process by _AmLHY_.