Transcriptomic Identification and Expression of Starch and Sucrose Metabolism Genes in the Seeds of Chinese Chestnut (Castanea mollissima)

Abstract

The Chinese chestnut (Castanea mollissima) seed provides a rich source of carbohydrates as food and feed. However, little is known about starch biosynthesis in the seeds. The objectives of this study were to determine seed composition profiles and identify genes involved in starch and sucrose metabolism. Metabolite analysis showed that starch was the major component and rapidly accumulated during seed endosperm development. Amylopectin was approximately 3-fold of amylose content in chestnut starch. Illumina platform-based transcriptome sequencing generated 56671 unigenes in two cDNA libraries from seed endosperms collected at 45 and 75 days after flowering (DAF). A total of 1537 unigenes showed expression differences ≥2-fold in the two stages of seeds including 570 up-regulated and 967 down-regulated unigenes. One hundred and fifty-two unigenes were identified as involved in starch and sucrose metabolism, including 1 for glycogenin glucosyltransferase, 4 for adenylate transporter (brittle1-type), 3 for ADP-glucose pyrophosphorylase (AGP, not brittle2- or shrunken2-type), 3 for starch synthase (SS), 2 for starch branching enzyme, 5 for starch debranching enzyme, 11 for sucrose synthase, and 3 for sucrose-phosphate synthase. Among them, 58 unigenes showed a ≥2-fold expression difference between the 45 and 75 DAF seeds including 11 up- and 47 down-regulated unigenes. The expression of 21 unigenes putatively coding for major enzymes in starch and sucrose metabolism was validated by qPCR using RNA from five seed stages. Expression profiles and correlation analysis indicated that the mRNA levels of AGP (large and small subunits), granule-bound SS2, and soluble SS1 and SS4 were well-correlated with starch accumulation in the seeds. This study suggests that the starch biosynthesis pathway in Chinese chestnut is similar to that of potato tuber/Arabidopsis leaf and differs from that of maize endosperm. The information provides valuable metabolite and genetic resources for future research in starch and sucrose metabolism in Chinese chestnut tree.

Identification and expression analysis of starch branching enzymes involved in starch synthesis during the development of chestnut (Castanea mollissima Blume) cotyledons

“…Amylopectin accounts for almost 75% of total starch in ripening chestnut, and the remaining 25% was amylose [21]. In our study, the ratio of amylopectin to amylose increased significantly through chestnut cotyledon development.…”

“…In Arabidopsis , SBE I did not expressed and its function was unknown, while SBE II had been classified into SBE 2.1 and SBE 2.2 [47]. Transcriptomic analysis of Chinese chestnut revealed two SBE unigenes; however, the isoforms and sequences of SBE were not defined [21]. In this study, we firstly identified and characterized two chestnut SBE isoforms involved in starch metabolism in chestnut by SDS-PAGE and MS analysis.…”

“…Chestnut is cultivated worldwide, and Chinese chestnut is native species in China [21]. According to Food and Agriculture Organization of the United Nations (FAO) statistics, the harvested area of Chinese chestnut was approximately 297,000 hm 2 in 2014, accounting for 56% of the harvested area worldwide and contributing to 82% of the world production [22].…”

“…According to Food and Agriculture Organization of the United Nations (FAO) statistics, the harvested area of Chinese chestnut was approximately 297,000 hm 2 in 2014, accounting for 56% of the harvested area worldwide and contributing to 82% of the world production [22]. Chestnut is mainly consumed after roast and high amylopectin content (approximately 3 fold of amylose) affects cooking quality by making the nut more glutinous [21, 23–24]. Despite the abundance of starch in the chestnut seed, little is known about the mechanistic relationship among starch synthesis-related enzymes, starch granule properties and key genes in starch synthesis pathway.…”

De novo transcriptome assembly for the five major organs of Zanthoxylum armatum and the identification of genes involved in terpenoid compound and fatty acid metabolism

“…Additionally, Wang et al [21] conducted a detailed transcriptional sequencing analysis of two orange varieties at different fruit development stages to elucidate the underlying regulatory mechanism of sucrose and citrate accumulation in the ripening of the fruits, especially during the fruit delayed-harvest stage. Zhang et al [23] explored the key regulatory factors involved in starch and sucrose metabolism in Castanea mollissima via transcriptome sequencing of seeds at various developmental stages. However, only a single study has reported transcriptome profiles obtained using a mixture of the leaves and inflorescences of Z. armatum to isolate the viruses associated with flower yellowing disease in recent years [24].…”