The understanding of floral development at a molecular level has proceeded at an unprecedented rate. Molecular genetic studies on two model plants, Antirrhinum and Arabidopsis in particular, have provided the foundation for this progress through the initial identification of genes involved in flowering. Recent efforts at elucidating the regulatory networks controlling the transition to flowering in the model plant Arabidopsis have identified over 80 independent loci, which have important roles in the control of flowering in this species. An even larger number of genes have been discovered controlling events downstream of floral initiation. This extensive compliment of genes also forms very complicated regulatory networks that integrate environmental and developmental mechanisms to coordinate the reproductive process. There have been many excellent review articles published recently, including those found in this volume, that provide an in-depth study of those genes involved in floral timing and floral organogenesis. The reader is encouraged to seek these out in order to appreciate the complexity inherent in the control of this vitally important developmental process.
[...] The relatedness between vine architecture and floral development combined with the apparent conservation of floral regulator sequence identity and expression pattern suggests fertile ground for agro-biotechnology approaches to assist in vine and grape improvement. The recent report of a mutation in the grape homologue of the Arabidopsis GAI gene indicates the important involvement of phytohormones, in particular GA, in the control of floral induction in this species. This is consistent with previous physiological studies. Another woody perennial, like grape, is the kiwifruit. [...]
[...] However, as described earlier, the overexpression of LFY in Arabidopsis and poplar results not only in the acceleration of flowering but also the malformation of floral organs suggesting that LFY expression alone in non-competent meristems is insufficient to trigger complete floral development and that additional unidentified factors are required. Vegetative to reproductive phase change The recently characterized BEL-1 like homeobox class gene regulators, PENNYWISE (PNY) and POUNDFOOLISH when combined as double mutants result in Arabidopsis plants whose meristems remain capable of receiving floral stimuli but are unable to complete the floral transition. [...]
[...] Floral development and biotechnology in woody perennial species In the following sections a brief overview of molecular studies in woody perennials is described. Grape and kiwifruit Like many woody species, grape requires an extended period of juvenile growth before the vine is competent to enter reproductive development. Unlike Arabidopsis where flowering commences after the perception of a suitable flowering stimulus, grapevines produce both vegetative and reproductive meristematic structures on the same shoot (Boss and Thomas, 2002). During shoot development the SAM produces a regular pattern of both leaf primordia and small meristematic protuberances termed uncommitted primordium. [...]
[...] The homeotic transformations caused by mutations of this sort and the results of ectopic over expression experiments automatically suggest the potential for biotechnology applications capable of rapidly altering reproductive development in agriculturally important crops without the difficulties associated with traditional breeding approaches. Although many genes involved in flowering have multiple roles both within flowering and in other developmental processes, there are a number of attractive ‘control points' that may be useful from a biotechnological point of view. Methods for gene discovery and manipulation Modern agro-biotechnology techniques are based on commonly used experimental techniques for gene discovery and functional analysis. [...]
[...] At this point those genes that direct the conversion of the vegetative meristem to an inflorescence or floral meristem can then act and offer opportunities to modify time to flowering. Mutants in these genes can act to delay or accelerate flowering under promotive or non-promotive environmental conditions. The flowering response in Arabidopsis can be considered in four main parts (all of which tend to be interconnected to give an integrated response to the environmental and developmental status): the autonomous pathway; the vernalization pathway; the gibberellin pathway; and the light-dependent pathway. [...]
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