Abstract
Flowering in orchids is the most important horticultural trait regulated by multiple mechanisms. Arundina graminifolia flowers throughout the year unlike other orchids with a narrow flowering span. However, little is known of the genetic regulation of this peculiar flowering pattern. This study identifies a number of transcription factor (TF) families in five stages of flower development and four tissue types through RNA-seq transcriptome. About 700 DEGs were annotated to the transcription factor category and classified into 35 TF families, which were involved in multiple signaling pathways. The most abundant TF family was bHLH, followed by MYB and WRKY. Some important members of the bHLH, WRKY, MYB, TCP, and MADS-box families were found to regulate the flowering genes at transcriptional levels. Particularly, the TFs WRKY34 and ERF12 possibly respond to vernalization and photoperiod signaling, MYB108, RR9, VP1, and bHLH49 regulate hormonal balance, and CCA1 may control the circadian pathway. MADS-box TFs including MADS6, 14, 16, AGL5, and SEP may be important regulators of flowering in A. graminifolia. Therefore, this study provides a theoretical basis for understanding the molecular mechanism of flowering in A. graminifolia.
Highlights
A. graminifolia starts the reproductive cycle after six months of vegetative growth
In the mature flower an equal number of up- and downregulated transcription factor (TF) can be seen (Figure 3c). These results suggest that the gene expression profiles of the samples obtained at the early and late flowering stages are quite different, and many genes may be highly expressed at the initial stage of flowering (FD5), and their expression may decrease as the flowers bloom and with age
By analyzing the interaction proteins of these key genes, we found many other important factors linked together, for example, short vegetative phase (SVP) is linked with leafy (LFY) and FLOWERING LOCUS T (FT)
Summary
Plants have developed several genetic mechanisms to assure flowering in various environmental conditions. These mechanisms are regulated by intrinsic and extrinsic signals [2]. Six flowering control pathways have been presented, including the ambient temperature pathway, vernalization pathway, circadian clock pathway, photoperiod pathway, gibberellin pathway, and autonomous pathway [3]. Photoperiod, and ambient temperature pathways, light and temperature act as extrinsic signals and are important environmental factors in the control of flowering [3,4]. Intrinsic signals are received by the circadian pathway, gibberellin pathway, and autonomous pathway to regulate flowering [5,6,7]
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