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

Abstract

Chinese chestnut (Castanea mollissima Blume) is native to China and distributes widely in arid and semi-arid mountain area with barren soil. As a perennial crop, chestnut is an alternative food source and acts as an important commercial nut tree in China. Starch is the major metabolite in nuts, accounting for 46 ~ 64% of the chestnut dry weight. The accumulation of total starch and amylopectin showed a similar increasing trend during the development of nut. Amylopectin contributed up to 76% of the total starch content at 80 days after pollination (DAP). The increase of total starch mainly results from amylopectin synthesis. Among genes associated with starch biosynthesis, CmSBEs (starch branching enzyme) showed significant increase during nut development. Two starch branching enzyme isoforms, CmSBE I and CmSBE II, were identified from chestnut cotyledon using zymogram analysis. CmSBE I and CmSBE II showed similar patterns of expression during nut development. The accumulations of CmSBE transcripts and proteins in developing cotyledons were characterized. The expressions of two CmSBE genes increased from 64 DAP and reached the highest levels at 77 DAP, and SBE activity reached its peak at 74 DAP. These results suggested that the CmSBE enzymes mainly contributed to amylopectin synthesis and influenced the amylopectin content in the developing cotyledon, which would be beneficial to chestnut germplasm selection and breeding.

Transcriptome Sequencing and Differential Expression Analysis Reveal Molecular Mechanisms for Starch Accumulation in Chestnut

“…In contrast, the percentages of soluble and reducing sugars decreased in the late Chinese chestnut maturation stage. Zhang et al [5] and Chen et al [6] reported the same trend from 45 to 75 DAF and 60 to 80 DAP in Chinese chestnut, respectively. A similar dynamic pattern was found in wheat with the soluble sugar content decreasing as the grain starch content increased [25].…”

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“…Despite the economic and social importance of bananas, there have been relatively fewer studies of bananas compared to other crops, especially in term of fruit development and response to environmental stress . SBE is a key enzyme in amylopectin synthetic pathway that has also been found to be involved in the regulation of seed germination, seedling growth and development, and in response to several abiotic/biotic stresses in many crops (Hamada et al, 2001;Xia et al, 2011;Pei et al, 2015;Chen et al, 2017;Li et al, 2017). In this study, we identified ten MaSBE genes through a genome-wide search of M. acuminata.…”

“…The SBE family genes have been reported to associate with the fruit development and ripening process in some plant species, including Malus × domestica (Han et al, 2007), Castanea mollissima (Chen et al, 2017),…”

“…In M. × domestica, SBE1 was found to express in low levels during the early stages of fruit development, and reached the highest expression during the middle stages of fruit development, implying regulatory control of SBE transcripts activity during apple fruit development (Han et al, 2007). In chestnut (C. mollissima), CmSBEI and CmSBEII were involved in starch synthesis and nut development (Chen et al, 2017). In kidney bean (P. vulgaris), SBE1 and SBE2 expression were closely related to amylopectin synthesis and seed maturation (Hamada et al, 2001).…”

“…For instance, a mutant deficient in SBEI activity in maize was found to have reduced kernel germination rate and coleoptile growth (Xia et al, 2011). Chestnut (Castanea mollissima) CmSBEI and CmSBEII were identified to play an important role in nut development and cotyledon growth (Chen et al, 2017). The expression studies of kidney bean (Phaseolus vulgaris) mutants pvsbe1 and pvsbe2 suggested pvsbe1 and pvsbe2 play a crucial role in mid-stage and late-stage of seed maturation, respectively (Hamada et al, 2001).…”