Cold stress triggers abscission through ABA-dependent signal
transduction in early developing apple
Abstract
Fruit abscission is a complex physiological process that is regulated by
internal and environmental factors. During early development, apple
fruit are exposed to extreme temperature fluctuations that are
associated with premature fruit drop; however, its effect on fruit
abscission is largely unknown. We hypothesized that fruit abscission is
triggered by cold stress and investigated the molecular basis of
premature fruit drop using RNA-seq and metabolomics data from apple
fruit undergoing abscission following cold stress in the field. Genes
responsive to abscisic acid signalling and cell wall degradation were
up-regulated during abscission, consistent with the increased abscisic
acid concentrations detected by LCMS. We performed ex-vivo cold shock
experiments with excised tree subunits consisting of a branch, pedicel,
and fruit. Abscission induction occurred in the cold-stressed subunits
with concurrent up-regulation of abscisic acid biosynthesis (MdNCED1)
and metabolism (MdCYP707A) genes, and ethylene biosynthesis (MdACS1) and
receptor (MdETR2) genes in pedicel. Another key finding was the
activation of cytoplasmic streaming of abscission-zone cells detected by
electron microscopy. Our results provide a novel insight into the
molecular basis of fruit abscission physiology in response to cold
stress in apple.