Mechanism of internal browning of pineapple: The role of gibberellins catabolism gene (AcGA2ox) and GAs
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.
[…] DNA sequence data were analyzed using the programs provided by the National Centre of Biotechnology (NCBI) web site (http://www.ncbi.nlm.nih.gov). The BLASTN and BLASTP programs were used for the gene sequence homology search. Amino acid sequences of selected plant GA-2oxidase genes were aligned using ClustalW2 (http://www.ebi.ac.uk/Tools/msa/clustalw2/). A phylogenetic tree was constructed using maximum parsimony with 500 bootstrap replicates of MEGA6.06. ExPASy web site (http://cn.expasy.org/tools/) and programs therein were used for the prediction of amino acid features of AcGA2ox. […]
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