Abstract
Exogenous ethylene, or ethephon, has been widely used to induce pineapple flowering, but the molecular mechanism behind ethephon induction is still unclear. In this study, we cloned four genes encoding ethylene receptors (designated AcERS1a, AcERS1b, AcETR2a, and AcETR2b). The 5′ flanking sequences of these four genes were also cloned by self-formed adaptor PCR and SiteFinding-PCR, and a group of putative cis-acting elements was identified. Phylogenetic tree analysis indicated that AcERS1a, AcERS1b, AcETR2a, and AcETR2b belonged to the plant ERS1s and ETR2/EIN4-like groups. Quantitative real-time PCR showed that AcETR2a and AcETR2b (subfamily 2) were more sensitive to ethylene treatment compared with AcERS1a and AcERS1b (subfamily 1). The relative expression of AcERS1b, AcETR2a, and AcETR2b was significantly increased during the earlier period of pineapple inflorescence formation, especially at 1–9 days after ethylene treatment (DAET), whereas AcERS1a expression changed less than these three genes. In situ hybridization results showed that bract primordia (BP) and flower primordia (FP) appeared at 9 and 21 DAET, respectively, and flowers were formed at 37 DAET. AcERS1a, AcERS1b, AcETR2a, and AcETR2b were mainly expressed in the shoot apex at 1–4 DAET; thereafter, with the appearance of BP and FP, higher expression of these genes was found in these new structures. Finally, at 37 DAET, the expression of these genes was mainly focused in the flower but was also low in other structures. These findings indicate that these four ethylene receptor genes, especially AcERS1b, AcETR2a, and AcETR2b, play important roles during pineapple flowering induced by exogenous ethephon.
Highlights
Pineapple (Ananas comosus L.) is one of the most popular tropical fruits
A previous study showed that higher ethephon concentrations inhibited the growth of ‘Zhenzhu’ pineapple fruits and that smaller fruits were harvested (Liu et al, 2009)
For ‘Perola’ pineapples, 200 or 1200 mg l−1 ethephon had no effect on the flowering rate, flowering time, or fruit qualities, such as fruit weight and number of fruitlets (Table 1)
Summary
In China and many other pineapple-planting regions, one of the most serious problems of pineapple cultivation is natural flowering, which results in unscheduled fruiting (Bartholomew et al, 2003). In China, natural flowering is often observed in February after the pineapples have experienced low temperatures in January or the previous December. This natural flowering results in most of the fruits being harvested from May to June; the natural flowering lasts for several weeks because it is not synchronized (Zhu et al, 2012), resulting in increased cultivation costs and decreased profit for pineapple growers. There has been much research concerning the role of ethylene in flower development (Lin et al, 2009), the molecular mechanism behind ethylene induction of flower development is still unclear
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