Abstract
Ethylene has long been considered the key regulator of ripening in climacteric fruit. Recent evidence showed that auxin also plays an important role during fruit ripening, but the nature of the interaction between the two hormones has remained unclear. To understand the differences in ethylene- and auxin-related behaviours that might reveal how the two hormones interact, we compared two plum (Prunus salicina L.) cultivars with widely varying fruit development and ripening ontogeny. The early-ripening cultivar, Early Golden (EG), exhibited high endogenous auxin levels and auxin hypersensitivity during fruit development, while the late-ripening cultivar, V98041 (V9), displayed reduced auxin content and sensitivity. We show that exogenous auxin is capable of dramatically accelerating fruit development and ripening in plum, indicating that this hormone is actively involved in the ripening process. Further, we demonstrate that the variations in auxin sensitivity between plum cultivars could be partially due to PslAFB5, which encodes a TIR1-like auxin receptor. Two different PslAFB5 alleles were identified, one (Pslafb5) inactive due to substitution of the conserved F-box amino acid residue Pro61 to Ser. The early-ripening cultivar, EG, exhibited homozygosity for the inactive allele; however, the late cultivar, V9, displayed a PslAFB5/afb5 heterozygous genotype. Our results highlight the impact of auxin in stimulating fruit development, especially the ripening process and the potential for differential auxin sensitivity to alter important fruit developmental processes.
Highlights
Fruit and seeds are essential for human nutrition
To assess the role of auxin in fruit development, a range of plum genotypes that vary in their flowering and ripening dates were selected and treated with naphthalene acetic acid (NAA) (Supplementary Table S2 available at JXB online)
Whereas auxin was once thought to be exclusively involved in the early stages of fruit development (S1 and S3), it is understood to be important during the S4 phase, where autocatalytic ethylene production is critical for the suite of changes that comprise the ripening process (Miller et al, 1987; Trainotti et al, 2007)
Summary
Fruit and seeds are essential for human nutrition. Postfertilization, fruits develop rapidly through a coordinated programme of molecular, biochemical and structural changes that optimize the potential for the development and dissemination of the seeds within. The fundamental importance of these processes has prompted considerable research into how they are governed. Research into fruit developmental processes has been greatly aided by analysing the outcome of both naturally occurring and induced genetic diversity (Kelly and Bradford, 1986; Lau et al, 2008). One outcome of this research has been the identification of phytohormones as master regulators of the many processes involved (McAtee et al, 2013). Auxin, GA, ABA, and cytokinin have all been shown to play important integrative roles
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