Abstract
Starch is one of the most important storage carbohydrates in plants. Kiwifruit typically accumulate large amounts of starch during development. The fruit retain starch until commercial maturity, and its postharvest degradation is essential for consumer acceptance. The activity of genes related to starch degradation has, however, rarely been investigated. Based on the kiwifruit genome sequence and previously reported starch degradation-related genes, 17 novel genes were isolated and the relationship between their expression and starch degradation was examined using two sets of materials: ethylene-treated (100 µL/L, 20 °C; ETH) vs. control (20 °C; CK) and controlled atmosphere stored (CA, 5% CO2 + 2% O2, 0 °C) vs. normal atmosphere in cold storage (NA, 0 °C). Physiological analysis indicated that ETH accelerated starch degradation and increased soluble solids content (SSC) and soluble sugars (glucose, fructose and sucrose), while CA inhibited starch reduction compared with NA. Using these materials, expression patterns of 24 genes that may contribute to starch degradation (seven previously reported and 17 newly isolated) were analyzed. Among the 24 genes, AdAMY1, AdAGL3 and AdBAM3.1/3L/9 were significantly induced by ETH and positively correlated with starch degradation. Furthermore, these five genes were also inhibited by CA, conforming the likely involvement of these genes in starch degradation. Thus, the present study has identified the genes with potential for involvement in starch degradation in postharvest kiwifruit, which will be useful for understanding the regulation of kiwifruit starch content and metabolism.
Highlights
Starch is widely distributed in plants and accumulates in various organs, such as leaves, seeds and tubers [1]
Based on a phylogenetic tree constructed with Arabidopsis homologs and the known kiwifruit genes, these seventeen newly isolated genes were designed as three AdAGL (AdAGL1-3; KX383662-4), four AdBAM (AdBAM2L, AdBAM3L, AdBAM7, AdBAM8; KX383648-51), three AdISA (AdISA1-3; KX383653-5), two AdDPE
Postharvest starch degradation was observed in Hayward kiwifruit, which was significantly accelerated by ethylene treatment and occurred concomitantly with rapid fruit softening [31]
Summary
Starch is widely distributed in plants and accumulates in various organs, such as leaves, seeds and tubers [1]. Starch is the major storable metabolite in many plants, and starch degradation is important in plant growth, especially at nighttime [2,3]. Arabidopsis mutants that synthesize less starch during the daytime and have lower starch degradation capacity at nighttime exhibited reduced growth rates [4,5]. Starch mainly accumulates during early fruit development, such as tomatoes [6] and apples [7]. High starch-containing fruit such as kiwifruit and bananas degrade starch to soluble sugars, once commercially harvested from vines [12]. Exploration of the mechanisms of starch degradation in fruit would benefit the understanding of the postharvest ripening of kiwifruit
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