Abstract
BackgroundThe formation and development of bulblets are crucial to the Lilium genus since these processes are closely related to carbohydrate metabolism, especially to starch and sucrose metabolism. However, little is known about the transcriptional regulation of both processes. To gain insight into carbohydrate-related genes involved in bulblet formation and development, we conducted comparative transcriptome profiling of Lilium davidii var. unicolor bulblets at 0 d, 15 d (bulblets emerged) and 35 d (bulblets formed a basic shape with three or four scales) after scale propagation.ResultsAnalysis of the transcriptome revealed that a total of 52,901 unigenes with an average sequence size of 630 bp were generated. Based on Clusters of Orthologous Groups (COG) analysis, 8% of the sequences were attributed to carbohydrate transport and metabolism. The results of KEGG pathway enrichment analysis showed that starch and sucrose metabolism constituted the predominant pathway among the three library pairs. The starch content in mother scales and bulblets decreased and increased, respectively, with almost the same trend as sucrose content. Gene expression analysis of the key enzymes in starch and sucrose metabolism suggested that sucrose synthase (SuSy) and invertase (INV), mainly hydrolyzing sucrose, presented higher gene expression in mother scales and bulblets at stages of bulblet appearance and enlargement, while sucrose phosphate synthase (SPS) showed higher expression in bulblets at morphogenesis. The enzymes involved in the starch synthetic direction such as ADPG pyrophosphorylase (AGPase), soluble starch synthase (SSS), starch branching enzyme (SBE) and granule-bound starch synthase (GBSS) showed a decreasing trend in mother scales and higher gene expression in bulblets at bulblet appearance and enlargement stages while the enzyme in the cleavage direction, starch de-branching enzyme (SDBE), showed higher gene expression in mother scales than in bulblets.ConclusionsAn extensive transcriptome analysis of three bulblet development stages contributes considerable novel information to our understanding of carbohydrate metabolism-related genes in Lilium at the transcriptional level, and demonstrates the fundamentality of carbohydrate metabolism in bulblet emergence and development at the molecular level. This could facilitate further investigation into the molecular mechanisms underlying these processes in lily and other related species.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0358-4) contains supplementary material, which is available to authorized users.
Highlights
The formation and development of bulblets are crucial to the Lilium genus since these processes are closely related to carbohydrate metabolism, especially to starch and sucrose metabolism
70% of these uniquely mapped to the reference genome (Table 2). 52,652 coding DNA sequences (CDSs) were predicted to have a mean length of 526 bp
The transcriptome was assembled with Trinity and functionally annotated with Blast2GO and Kyoto Encyclopedia of Genes and Genomes (KEGG)
Summary
The formation and development of bulblets are crucial to the Lilium genus since these processes are closely related to carbohydrate metabolism, especially to starch and sucrose metabolism. To gain insight into carbohydrate-related genes involved in bulblet formation and development, we conducted comparative transcriptome profiling of Lilium davidii var. Unicolor, a mutation of L. davidii Duchartre, is an important genus, both economically and ornamentally, in Lanzhou, Gansu province in PR China. It is renowned for its large size, white and thick flesh as well as sweet taste [3], and its flaming and flamboyant color provide its ornamental value. L. davidii var. unicolor bulbs, which are considered health food due to their abundant nutritional value (11.46% starch, 10.39% sucrose, 5.61% pectin, 3.36% protein), are used in Chinese medicine in different forms as fresh bulbs, dried scales, as well as powder to treat heart and lung ailments [5]
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