Abstract
Auxin has been suggested to play an essential role in regulating apple fruit maturation and ripening, though the molecular function of auxin and its interaction with ethylene during apple fruit development are largely unknown. To understand the function of auxin during apple fruit maturation and ripening, auxin efflux carrier and IAA-amido synthetase encoding genes were identified from the apple genome based on the results of previous microarray analysis. The expression patterns of these genes were analyzed using qRT-PCR during 10 - 12 weeks of fruit maturation for two apple cultivars: “Golden Delicious” (GD) and “Cripps Pink” (CP), which have the distinct patterns of maturation progression. Our results showed that the expressions of auxin efflux carrier and IAA-amido synthetase genes have a correlation with the timing of ethylene biosynthesis pathway activation in both cultivars. The earlier and stronger expression of MdGH3.102 and MdAECFP1 in the fruit of GD, a mid-season cultivar, correlates with the earlier activation of a pre-climacteric ethylene biosynthesis gene of MdACS3, compared with that in CP, a late-ripening apple cultivar. Results of exogenous IAA treatment indicated that the expression patterns of the genes were regulated in a fruit maturity dependent manner. Our results suggested that the dynamics of the auxin level in apple fruit cortex could be one of the key factors influencing the timing of ethylene biosynthesis pathway activation and consequently contributed to the control of the apple maturation progression.
Highlights
Fruit maturation and ripening are tightly regulated by multiple genetic factors [1]-[3]
Fruit internal ethylene concentration (IEC) for both cultivars showed a low-level fluctuation which is typical in pre-climacteric apple fruit
Based on the differential expression profiles of genes with annotated function of auxin transport and conjugation in maturing apple, the results provided the preliminary molecular evidences at transcriptional level on the potential connection between auxin availability and ethylene biosynthesis pathway activation
Summary
Fruit maturation and ripening are tightly regulated by multiple genetic factors [1]-[3]. Under specific cellular contexts, such as in maturing apple fruit, the modulation of the gene expression depends on the integration of multiple inputs of developmental or environmental signals. Among these signals, crosstalk between plant hormones is believed to be one of the important aspects which control fruit development [4]-[7]. Specific to climacteric fruit such as apple, ethylene is well-known to play a pivotal role in the ripening regulation [8]-[11]. Recent transcriptomic and genomic studies indicated the roles of auxin and its potential interactions with ethylene during apple fruit maturation and ripening [13] [14], but the details of the interactions are unknown
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