Genetic insights into the regulatory pathways for continuous flowering in a unique orchid Arundina graminifolia

Abstract

Background Manipulation of flowering time and frequency of blooming is key to enhancing the ornamental value of orchids. Arundina graminifolia is a unique orchid that flowers year round, although the molecular basis of this flowering pattern remains poorly understood. Results We compared the A. graminifolia transcriptome across tissue types and floral developmental stages to elucidate important genetic regulators of flowering and hormones. Clustering analyses identified modules specific to floral transition and floral morphogenesis, providing a set of candidate regulators for the floral initiation and timing. Among candidate floral homeotic genes, the expression of two FT genes was positively correlated with flower development. Assessment of the endogenous hormone levels and qRT-PCR analysis of 32 pathway-responsive genes supported a role for the regulatory networks in floral bud control in A. graminifolia. Moreover, WGCNA showed that flowering control can be delineated by modules of coexpressed genes; especially, MEgreen presented group of genes specific to flowering. Conclusions Candidate gene selection coupled with hormonal regulators brings a robust source to understand the intricate molecular regulation of flowering in precious orchids.

The Genetic and Hormonal Inducers of Continuous Flowering in Orchids: An Emerging View

“…MADS14 is an AP1/FRUITFUL (FUL)-like MADS-box TF that involves meristem identity [ 44 , 45 , 46 ]. MADS14 and MADS16 , an AP3 - PI subfamily genes, and SEP were highly expressed in the early stages of flower development of A. graminifolia [ 1 , 26 ]. In Phalaenopsis hybrid Athens, SEP -like genes ( PhaMADS4 , PhaMADS5 and PhaMADS7 ) express in floral organs [ 47 ].…”

“…Flowering plants dominate the terrestrial landscape and, therefore, play a pivotal role in human life. Plant species adjust their flowering times using a fine combination of internal and external stimuli to adapt to the versatile environments [ 1 ]. Therefore, floral timing is one of the most important horticultural characteristics of floriculture crops, and a stable time of flowering is the main goal of breeding programs to induce horticultural novelty in commercial crops.…”

“…Flowering signals are transmitted by these integrators to the floral meristem identity genes, such as LFY ( LEAFY ) and AP1 ( APETALA1 ). The activation of meristem identity genes is followed by floral development in association with MADS-box genes and co-regulators [ 1 , 5 ].…”

“…Orchidaceae contains the most important ornamental flowers [ 6 , 7 ], and that is why more than 0.1 million orchid species are cultivated throughout the world [ 1 ]. Such a beauty waits a long time to flower.…”

“…Phalaenopsis , Cymbidium and Dendrobium are among the most attractive flowers, which bloom in specific seasons [ 8 ]. However, there is an orchid species, Arundina graminifolia , which gives continuous flowering throughout the year unlike other orchids [ 1 ]. Finding the key regulators of this continuous flowering pattern can provide a valuable source to find applicable solutions to seasonal flowering orchids.…”