Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2015
Publication Date: 3/7/2015
Citation: Shin, S.B., Lee, J., Rudell Jr, D.R., Evans, K., Zhu, Y. 2015. Transcript profiles of auxin efflux carrier and IAA-amido synthetase genes suggest the role of auxin on apple (Malus x domestica) fruit maturation patterns. American Journal of Plant Sciences. 6:620-630.
Interpretive Summary: Our previous large-scale transcriptome analysis has indicated that auxin transport and conjugation during apple fruit development may play an important role in ripening regulation, in addition to well-elucidated function of ethylene. This study is to test the hypothesis that auxin metabolisms in apple fruit may play a key role of initiating the ethylene biosynthesis pathway activation, and determining genotype-specific ripening season. Among apple cultivars their ripening seasons vary greatly; even within the elite commercial cultivars the harvest times can span almost three months from early August to late October in northern hemisphere. Fruit quality such as at-harvest fruit firmness and postharvest storability are closely associated with fruit ripening patterns and harvest seasons. To understand the genetic basis controlling this economically important trait, the transcriptional regulation of genes functioning in auxin transport, auxin conjugation and ethylene biosynthesis between two apple cultivars, ‘Golden Delicious’ and ‘Cripps Pink’, with the contrasting ripening dynamics was studied. The expression patterns of MdGH3.1 and MdAECFP1 are correlated with apple fruit on-tree maturity progression and the timing of ethylene biosynthesis pathway activation. Exogenous auxin treatment on the fruit from two cultivars resulted in the differential responses on the expression of these genes suggesting maturity-specific sensitivity of these genes to auxin. Our data suggested that the availability of auxin due to transportation and conjugation is crucial to activate ethylene production, and may play a major role on the ripening time of a given cultivar.
Technical Abstract: Plant growth regulators are known to regulate fruit development at various stages including flowering, fruit growth, maturation and ripening. Recent transcriptome studies indicated that auxin might play an essential role in regulating apple fruit maturation and ripening beside the well-defined roles of ethylene. However, the molecular function of auxin and its interaction with ethylene during apple fruit ripening is largely unknown. To get insight of the role of auxin in apple fruit maturation and ripening, apple genes encoding auxin transporter and conjugation enzymes, i.e. Auxin Efflux Carrier and IAA-amido synthetase, were identified from the apple genome based on the results of previous microarray analysis. The expression patterns of these genes were characterized during fruit maturation for two apple cultivars ‘Golden Delicious’ and ‘Cripps Pink (Pink LadyTM)’ with contrasting ripening phenotypes. The gene expression patterns around physiological maturity of apple fruit were profiled using qRT-PCR method using at least 10 consecutive weekly samples. Our results suggested that the availability of auxin in the cell may determine the timing of ethylene biosynthesis pathway activation through the expression of a pre-climacteric ethylene biosynthesis gene (MdACS3) and subsequent ripening progression. Exogenous IAA treatment indicated that genes encoding proteins functioning in auxin transport and conjugation, as well as ethylene biosynthesis genes, were regulated in a fruit maturity dependent manner.