Submitted to: Journal of Plant Growth Regulation
Publication Type: Other
Publication Acceptance Date: 11/17/2015
Publication Date: 1/26/2016
Citation: Shin, S.B., Lee, J., Rudell Jr, D.R., Evans, K.C., Zhu, Y. 2016. Transcriptional regulation of auxin metabolism and ethylene biosynthesis activation during apple (Malus × domestica) fruit maturation. Journal of Plant Growth Regulation. 35:655-666.
Interpretive Summary: 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 for the control of this economically important trait, and based on the results from our previous large-scale transcriptome profiling, the current experiment was designed to understand the molecular events related to auxin ethylene interactions during apple fruit development. At least 10 consecutive weeks of on-tree maturing fruit were carefully monitored for their physiological change and gene activity related to auxin metabolism. Specifically, the expression of eight candidate genes with annotated functions of auxin transport, conjugation and responses, as well as ethylene biosynthesis gene MdACS3, were profiled by qPCR. Most of these genes showed dynamic regulation during fruit development and differential expression among cultivars. Our data suggested that auxin transport and availability could be a crucial factor triggering ethylene production, and therefore regulating the ripening time.
Technical Abstract: Variation exists among apple genotypes in fruit maturation and ripening patterns that influences at13 harvest fruit firmness and postharvest storability. Based on the results from our previous large-scale 14 transcriptome profiling on apple fruit maturation and well-documented auxin-ethylene crosstalk, the 15 current experiment was designed to understand the molecular events related to auxin metabolism during 16 fruit development and their interactions with ethylene pathways. Maturity-defined weekly apple fruit 17 samples of four cultivars with distinct ripening phenotypes were aligned according to their physiological 18 maturity. The expression of eight candidate genes with annotated functions of auxin transport, 19 conjugation and responses were profiled by qPCR for at least 10 consecutive weeks; and the weekly 20 sample with similar Ct values were selected as calibrators of relative expression level for better across21 genotype comparability. Most of these genes showed dynamic regulation during fruit development and 22 differential expression among cultivars. Transcript profiles for these genes during fruit maturation and 23 tissue-specific expression features suggested that auxin transport and homeostasis could be a crucial 24 factor in regulating the timing of ethylene pathway activation. The peak expression of auxin transporter 25 MdPIN1-1 correlated with the detection of the transcripts of a pre-climacteric ethylene biosynthesis gene 26 MdACS3, and therefore may contribute to distinct ripening processes among apple genotypes.