Transcriptome Analysis Identifies a Zinc Finger Protein Regulating Starch Degradation in Kiwifruit

Abstract

Ripening, including softening, is a critical factor in determining the postharvest shelf-life of fruit and is controlled by enzymes involved in cell wall metabolism, starch degradation, and hormone metabolism. Here, we used a transcriptomics-based approach to identify transcriptional regulatory components associated with texture, ethylene, and starch degradation in ripening kiwifruit (<i>Actinidia deliciosa</i>). Twelve differentially expressed structural genes, including seven involved in cell wall metabolism, four in ethylene biosynthesis, and one in starch degradation, and 14 transcription factors (TFs) induced by exogenous ethylene treatment and inhibited by the ethylene signaling inhibitor 1-methylcyclopropene were identified as changing in transcript levels during ripening. Moreover, analysis of the regulatory effects of differentially expressed genes identified a zinc finger TF, DNA BINDING WITH ONE FINGER (AdDof3), which showed significant transactivation on the <i>AdBAM3L</i> (β-amylase) promoter. AdDof3 interacted physically with the <i>AdBAM3L</i> promoter, and stable overexpression of <i>AdBAM3L</i> resulted in lower starch content in transgenic kiwifruit leaves, suggesting that <i>AdBAM3L</i> is a key gene for starch degradation. Moreover, transient overexpression analysis showed that AdDof3 up-regulated <i>AdBAM3L</i> expression in kiwifruit. Thus, transcriptomics analysis not only allowed the prediction of some ripening-regulating genes but also facilitated the characterization of a TF, AdDof3, and a key structural gene, <i>AdBAM3L</i>, in starch degradation.