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Genes Associated with Orchid Flower
Soek Ying Neo and Kwok Ki Ho
The National University of Singapore, Singapore, Republic of Singapore
549I. INTRODUCTION
Orchids are a globally important flower crop. It has been estimated that in the year 2000 there was a
worldwide demand of 1600 million units of planting material, and the majority of this was produced by
the tissue culture method and used for mass cultivation in Southeast Asian countries [1]. To date, clonal
propagation of orchids has been extended to more than 43 genera [2]. Moreover, the physiology of some
orchid species in Cymbidium, Dendrobium, Phalaenopsis, and Oncidiumhas been studied intensively
over the past decades, and this has led to the establishment of recommendations for flower induction and
storage [2]. Despite the advances made in these areas, numerous questions related to flower production
remain to be investigated. Examples are how to increase harvestable flower yield, how to control flower-
ing to meet market demand, how to prolong the vase life of cut flowers, and how to enhance their aes-
thetic properties such as color and architecture. Such questions can be addressed with a better under-
standing of the genetic factors affecting such physiological processes including flower production and
development, flowering time, senescence, and pigmentation. Careful examination of the orchid literature
published over the past decade, particularly from a survey of the molecular database, indicates that re-
searchers are beginning to reveal genes closely associated with these processes (Table 1) and are poised
to make further progress in the next few years. In this chapter, we describe what is known to date about
these orchid genes in relation to our current knowledge of their counterparts in other plant systems. It is
hoped that this chapter will stimulate interest in further investigation of these and other genes associated
with the biology of the orchid flower.
II. FLOWER DEVELOPMENT
Over the past decade, there has been considerable progress in our understanding of floral development at
the molecular level. From mutational studies of flower development in some plant species, a large num-
ber of genes associated with the transition of the apical vegetative meristem to the floral meristem have
been identified [24]. For some, their roles in controlling the transition and organogenesis have been
clearly demonstrated, whereas for others, their roles remain to be defined. It is now appreciated that the
process of flower development involves two classes of consecutively acting regulatory genes that encode
transcription factors. First, meristem-identity genes, expressed throughout the incipient floral primordia,