Transcript Profiles of Auxin Efflux Carrier and IAA-Amido Synthetase Genes Suggest the Role of Auxin on Apple (<i>Malus</i> × <i>domestica</i>) Fruit Maturation Patterns

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.

Climacteric ripening of apple fruit is regulated by transcriptional circuits stimulated by cross-talks between ethylene and auxin

“…Our recent results, together with those of other Authors, 22,23,24,25 shed light on the possible ethylene/auxin cross-talk in rosaceae species triggered by the interference at the receptor level (depicted in Fig. 2).…”

An apple somatic mutation of delayed fruit maturation date is primarily caused by a retrotransposon insertion‐associated large deletion

“…The involvement of Mod2 member genes was likely through the enriched auxin related pathways, as auxin is well known for its role in flesh fruit maturation and ripening (Fenn & Giovannoni, 2021). In apple, the reduction of auxin contents in fruit flesh tissues in late development stages has been shown to be necessary in order to activate the ethylene biosynthesis pathway required for advancing the fruit maturation process (Shin et al., 2015; Shin et al., 2016). It would be of great interest to investigate if and how MdACT7 and the MdSAUR member genes in Mod2 would be involved in variation of the fruit flesh auxin contents prior to the onset of apple fruit ripening.…”

Postharvest quality of ‘Brookfield’ apple field-treated with naphthalene acetic acid alone or combined with other growth regulators

“…The preharvest application of NAA decreases fruit abscission due to the reduction in gene expression of enzymes involved in the degradation of cell wall in the abscission zone (Li and Yuan 2008), since the application of NAA increases auxin levels in fruit (Yuan and Carbaugh 2007). There is a complex relationship among auxin and ethylene functions in apple fruit, which are related to gene family members and fruit developmental stages (Shin et al 2015). The NAA increases the expression of genes related to the ethylene biosynthesis (MdACS1 and MdACO1), perception (MdERS1) and cell wall degradation enzymes (MdPG1) L. M. Wendt et al (Li and Yuan 2008;Yuan and Li 2008), therefore decreasing the storage potential of the fruit (Brackmann et al 2014;Brackmann et al 2015a).…”