Abstract
Internal browning (IB), a physiological disorder (PD) that causes severe losses in harvested pineapple, can be induced by exogenous gibberellins (GAs). Over the years, studies have focused on roles of Gibberellin 2-oxidase (GA2oxs), the major GAs catabolic enzyme in plants, in the regulation of changes in morphology or biomass. However, whether GA2oxs could regulate PD has not been reported. Here, a full-length AcGA2ox cDNA was isolated from pineapple, with the putative protein sharing 23.59% to 72.92% identity with GA2oxs from five other plants. Pineapples stored at 5 °C stayed intact, while those stored at 20 °C showed severe IB. Storage at 5 °C enhanced AcGA2ox expression and decreased levels of a GAs (GA4) ‘compared with storage at 20 °C. However, at 20 °C, exogenous application of abscisic acid (ABA) significantly suppressed IB. ABA simultaneously upregulated AcGA2ox and reduced GA4. Ectopic expression of AcGA2ox in Arabidopsis resulted in reduced GA4, lower seed germination, and shorter hypocotyls and roots, all of which were restored by exogenous GA4/7. Moreover, in pineapple, GA4/7 upregulated polyphenol oxidase, while storage at 5 °C and ABA downregulated it. These results strongly suggest the involvement of AcGA2ox in regulation of GAs levels and a role of AcGA2ox in regulating IB.
Highlights
Germination in the absence of light and cold stimuli, delay the vegetative and floral phase transitions, limit the number of flowers produced per inflorescence, suppress elongation of the pistil prior to fertilization[19], influence underground biomass growth of Populus[20], and affect fruit set and growth in tomato[21]
Through displaying the expression patterns of AcGA2ox gene in response to a series of treatments that regulate GA levels and Internal browning (IB) development in pineapple, in combination with the phenotypes connected with deficiency in bioactive GAs of Arabidopsis lines overexpressing AcGA2ox, we show that enhanced expression of AcGA2ox resulted in lower bioactive GA levels and suppressed IB development
Transient expression of AcGA2ox in protoplasts of Arabidopsis mesophyll indicates that it was localized in cytoplasm (Fig. S2)
Summary
Germination in the absence of light and cold stimuli, delay the vegetative and floral phase transitions, limit the number of flowers produced per inflorescence, suppress elongation of the pistil prior to fertilization[19], influence underground biomass growth of Populus[20], and affect fruit set and growth in tomato[21]. Our recent work suggested that downregulation of a GA2ox could be related to the delay of senescence of a harvested leafy vegetable[22]. To the authors’ knowledge, there has not been any study on the role GA2oxs in regulating PD. IB is an ideal PD for addressing the role of GA2oxs. Studying AcGA2ox gene in the context of IB would surely add to the understanding of the functions of GA2oxs gene family. Through displaying the expression patterns of AcGA2ox gene in response to a series of treatments that regulate GA levels and IB development in pineapple, in combination with the phenotypes connected with deficiency in bioactive GAs of Arabidopsis lines overexpressing AcGA2ox, we show that enhanced expression of AcGA2ox resulted in lower bioactive GA levels and suppressed IB development
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