Metabolic analysis of kiwifruit (Actinidia deliciosa) berries from extreme genotypes reveals hallmarks for fruit starch metabolism

Abstract

Tomato, melon, grape, peach, and strawberry primarily accumulate soluble sugars during fruit development. In contrast, kiwifruit (Actinidia Lindl. spp.) and banana store a large amount of starch that is released as soluble sugars only after the fruit has reached maturity. By integrating metabolites measured by gas chromatography–mass spectrometry, enzyme activities measured by a robot-based platform, and transcript data sets during fruit development of Actinidia deliciosa genotypes contrasting in starch concentration and size, this study identified the metabolic changes occurring during kiwifruit development, including the metabolic hallmarks of starch accumulation and turnover. At cell division, a rise in glucose (Glc) concentration was associated with neutral invertase (NI) activity, and the decline of both Glc and NI activity defined the transition to the cell expansion and starch accumulation phase. The high transcript levels of β-amylase 9 (BAM9) during cell division, prior to net starch accumulation, and the correlation between sucrose phosphate synthase (SPS) activity and sucrose suggest the occurrence of sucrose cycling and starch turnover. ADP-Glc pyrophosphorylase (AGPase) is identified as a key enzyme for starch accumulation in kiwifruit berries, as high-starch genotypes had 2- to 5-fold higher AGPase activity, which was maintained over a longer period of time and was also associated with enhanced and extended transcription of the AGPase large subunit 4 (APL4). The data also revealed that SPS and galactinol might affect kiwifruit starch accumulation, and suggest that phloem unloading into kiwifruit is symplastic. These results are relevant to the genetic improvement of quality traits such as sweetness and sugar/acid balance in a range of fruit species.

Characterization of Ripening-related Genes Involved in Ethylene-independent Low Temperature-modulated Ripening in ‘Rainbow Red’ Kiwifruit during Storage and On-vine

“…Sugar accumulation is attributed to hydrolysis of starch by β-amylase (Nardozza et al, 2013;Richardson et al, 2011), and metabolism of sucrose by sucrose synthase (Moscatello et al, 2011). In the present study, the expression of AcSUS and AcβAMY1 increased in propylene-treated fruit and both during storage and onvine ripening, accounting for the increase in SSC observed ( Fig.…”

Comprehensive Transcriptome Profiling Reveals Long Noncoding RNA Expression and Alternative Splicing Regulation during Fruit Development and Ripening in Kiwifruit (Actinidia chinensis)

“…Sweetness is the most important quality trait for kiwifruit as it influences overall fruit flavor (sugar/acid balance, perception of volatiles), and determines consumer acceptability (Nardozza et al, 2013). Most breeding programmes, however, have a negative impact on this trait.…”

Characterization of Starch Degradation Related Genes in Postharvest Kiwifruit

“…Three AdAMY ( AdAMY1-3 ) and four AdBAM ( AdBAM1 , AdBAM3.1 , AdBAM3.2 and AdBAM9 ) genes were reported and analyzed for starch metabolism during kiwifruit development [29]. In addition to these seven known genes, seventeen genes encoding enzymes potentially related to starch degradation were isolated, using the kiwifruit genome database (Figure 1).…”

“…Among the five banana genes, Ma-bmy showed increasing expression patterns during postharvest storage [10]. In kiwifruit, several starch related genes ( AdAMY1-3 , AdBAM1 , AdBAM3.1 , AdBAM3.2 and AdBAM9 ) were reported using a kiwifruit expressed sequence tags (EST) database [29]; however, their expression was only analyzed during kiwifruit development (starch accumulation), but not postharvest storage (starch degradation). Thus, the molecular studies on postharvest fruit starch degradation are lacking.…”