Isolation of flowering genes and seasonal changes in their transcript levels related to flower induction and initiation in apple (Malus domestica)

Abstract

Flower development in apple (Malus domestica Borkh.) extends over two consecutive seasons. During the first season, most shoot apical meristems change to reproductive growth and initiate flowers. After winter dormancy, flower development continues during the second season and ends with anthesis in the spring. To determine the beginning of the transition to reproductive growth at the molecular level and to identify genes involved in this critical phase of flower development, we examined transcript levels of the putative flowering genes MdCOL1, MdCOL2, MdFT, MdSOC1, MdMADS2, MdMADS5, MdTFL1-1 and MdTFL1-2 in vegetative terminal buds of the apple cultivar Pinova during the first season by quantitative real-time PCR. Transcript levels of these genes peaked at the end of April during blooming of coexisting floral buds. Subsequently, there was a large increase in transcription, which started on May 22 for AFL2 and MdMADS2, followed by MdFT and AFL1 one week later. We propose that the increased transcription at the end of May marks the beginning of flower induction. Transcript levels of MdSOC1, MdTFL1-1 and MdTFL1-2 increased at the end of June, suggesting that these genes are involved in flower initiation, which follows flower induction. In contrast, MdMADS5 transcription was too weak to be quantified, and the transcript levels of MdCOL1 and MdCOL2 showed no detectable trends during the study.

Relationship between MdMADS11 Gene Expression and Juvenility in Apple

“…Because there is a lack of information on the relationship between AGL6 homologs and seasonal flower initiation, seasonal changes in MdMADS11 gene expression were analyzed in adult apple trees. A rapid decrease in the abundance of MdMADS11 mRNA in leaf buds with putative seasonal flower initiation is interesting because MdMADS11 may promote flowering; however, unlike that described for MdFT (Hättasch et al, 2008;Kotoda et al, 2010) no peak in flower buds was detected in MdMADS11 expression, suggesting that other factors are involved in the control of seasonal flower initiation. In addition, AGL6 homologs may play a role in floral organ formation, as described in orchids, petunia, and rice (Hsu et al, 2006;Ohmori et al, 2009;Rijpkema et al, 2009).…”

“…FT homologs may play a role in seasonal flower initiation in the adult phase of poplar, citrus, and apple, because they are highly expressed during the seasonal flowering period (Hättasch et al, 2008;Hsu et al, 2006;Kotoda et al, 2010;Nishikawa et al, 2007). Because there is a lack of information on the relationship between AGL6 homologs and seasonal flower initiation, seasonal changes in MdMADS11 gene expression were analyzed in adult apple trees.…”

“…The abundance in leaf buds was high from early May to late June and subsequently decreased in mid-July, whereas that in flower buds did not decrease. Although MdFT expression was previously described by Hättasch et al (2008) and Kotoda et al (2010), it was determined in this study to provide a reference for flowering induction and initiation (Fig. 5c).…”

Expression Pattern of Several Flowering-related Genes during Flower Bud Formation in Rhododendron × pulchrum ‘Oomurasaki’

“…Thus, the present results indicate that the expression patterns of RpFT, RpLFY, RpTFL1, and RpAP3 correspond with morphological changes during floral development of 'Oomurasaki'. Interestingly, with regard to the relationship between floral development and the expression pattern of flowering-related genes, Hättasch et al (2008) reported that if the expression pattern of FT, AFL, and TFL1 homologs in apple shoots was investigated by quantitative transcription analysis, the timing of floral bud formation could be identified. In evergreen azalea 'Oomurasaki', the expression pattern of RpFT, RpLFY, RpTFL1, and RpAP3 was used to determine the period of floral bud formation.…”

Precocity and a long-term cropping in apple progenies grown on M 9 rootstock

“…Several genes are involved in the critical phase of flower development and their effect in flower induction is probably influenced by the level of fruit set (Hattasch et al 2008).…”