Abstract
In sweet cherry trees, flowering is commercially important because the flowers, after fertilization, will generate the fruits. In P. avium, the flowering induction and flower organogensis are the first developmental steps towards flower formation and they occur within specialized organs known as floral buds during the summer, nine months before blooming. During this period the number of floral buds per tree and the bud fruitfulness (number of flowers per bud) are stablished affecting the potential yield of orchards and the plant architecture. The floral bud development is sensitive to any type of stress and the hotter and drier summers will interfere with this process and are calling for new adapted cultivars. A better understanding of the underlying molecular and hormonal mechanisms would be of help, but unlike the model plant Arabidopsis, very little is known about floral induction in sweet cherry. To explore the molecular mechanism of floral bud differentiation, high-throughput RNA sequencing was used to detect differences in the gene expression of P. avium floral buds at five differentiation stages. We found 2,982 differentially expressed genes during floral bud development. We identified genes associated with floral initiation or floral organ identity that appear to be useful biomarkers of floral development and several transcription factor families (ERF, MYB, bHLH, MADS-box and NAC gene family) with novel potential roles during floral transition in this species. We analyzed in deep the MADS-box gene family and we shed light about their key role during floral bud and organs development in P. avium. Furthermore, the hormonal-related signatures in the gene regulatory networks and the dynamic changes of absicic acid, zeatin and indolacetic acid contents in buds suggest an important role for these hormones during floral bud differentiation in sweet cherry. These data provide a rich source of novel informacion for functional and evolutionary studies about floral bud development in sweet cherry and new tools for biotechnology and breeding.
Highlights
Sweet cherry (P. avium) is perennial fruit tree that has a distinctive mode of reproductive development that differs significantly from Arabidopsis and annual species
We found hormonal-related signatures, mainly associated to abscisic acid, auxins and citokinins, in the floral bud transcriptomes and we evaluated the dynamic changes of absicic acid (ABA), zeatin (Z) and indolacetic acid (IAA) levels in floral buds and bud-adjacent leaves in order to determinate their potential role during floral transitions in sweet cherry
The flower primordium appears as a dome with five sepal and within it, the floral whorls continued their development and the petal, stamen and pistil primordias were evidenced (Fig 1C, 1G and 1K) (Feb. 15)
Summary
Sweet cherry (P. avium) is perennial fruit tree that has a distinctive mode of reproductive development that differs significantly from Arabidopsis and annual species. In sweet cherry (P. avium) trees, the flowering induction and many factors related to floral bud development (such as flower bud density, bud fruitfulness, double pistils and flower quality) are very important because they can influence the productivity and to determine in a considerable extent the commercial success of orchards[3]. These traits affect directly the potential crop yield as well as the plant architecture and several cultural practices (e.g. type of pruning employed)[4]. Variations in floral buds per tree, bud fruitfulness and flower development anomalies (double pistilated flowers) would be in part responsible for the inconsistent yields observed among years[5,6], converting the induction and initiation stage of flowering within the floral bud in a relevant process for stone fruit-industry interests
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