Analysis of gene expression and enzyme activities related to starch metabolism in Lycoris sprengeri bulbs of different sizes

Abstract Differentially expressed genes related to starch metabolism in mature and juvenile bulbs of Lycoris sprengeri were screened via tag-based digital gene expression profiling. The relative expression levels of these genes were further verified by quantitative real-time polymerase chain reaction. Related enzyme activities and carbohydrate concentrations were determined to study the molecular mechanism of starch accumulation during bulb development. Four starch metabolic genes ( LsBAM1 , LsAMY1 , LsAMY3 and LsSS1 ) were differentially expressed between the mature and juvenile bulbs. LsSS1 is utilised during starch synthesis and the three other genes are utilised for starch degradation. The expressions of the four genes were significantly higher in juvenile bulbs than in mature bulbs. Along with bulb development (seven sizes, from bulblets to mature bulbs), β-amylase (BAM) activity significantly increased whereas α-amylase (AMY) activity slightly fluctuated. The expression levels of LsBAM1 , LsAMY1 and LsAMY3 were either negatively correlated or not correlated with BAM and AMY activities. Soluble starch synthase (SSS) activity increased with decreased LsSS1 expression whereas granule-bound starch synthase (GBSS) activity decreased, indicating a positive correlation with the decreased expression level of LsSS1 . During bulb development, the carbohydrate concentrations increased. In the largest mature bulbs, the highest concentration of total soluble sugar coincided with the highest β-amylase activity. However, no evidence was found to confirm the relationship between this phenomenon and related gene expression. The results revealed preliminary characteristics related to starch metabolism during the bulb development of L. sprengeri .