Li XueYan, Wang ChunXia, Cheng JinYun, Zhang Jing, da Silva Jaime A Teixeira, Liu XiaoYu, Duan Xin, Li TianLai, Sun HongMei
BMC Plant Biol. 2014 Dec 19;14:358. doi: 10.1186/s12870-014-0358-4.
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. 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.
Analysis 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.
An 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.
小鳞茎的形成和发育对百合属植物至关重要，因为这些过程与碳水化合物代谢密切相关，尤其是与淀粉和蔗糖代谢相关。然而，对于这两个过程的转录调控知之甚少。为了深入了解参与小鳞茎形成和发育的碳水化合物相关基因，我们对兰州百合小鳞茎在鳞片扦插繁殖后0天、15天（小鳞茎出土）和35天（小鳞茎形成具有三到四片鳞片的基本形状）进行了比较转录组分析。
转录组分析显示，共产生了52,901个单基因，平均序列大小为630 bp。基于直系同源簇（COG）分析，8%的序列属于碳水化合物运输和代谢。KEGG通路富集分析结果表明，淀粉和蔗糖代谢是三个文库对中的主要通路。母鳞片和小鳞茎中的淀粉含量分别下降和增加，趋势与蔗糖含量几乎相同。淀粉和蔗糖代谢关键酶的基因表达分析表明，主要水解蔗糖的蔗糖合酶（SuSy）和转化酶（INV）在小鳞茎出现和膨大阶段的母鳞片和小鳞茎中呈现较高的基因表达，而蔗糖磷酸合酶（SPS）在形态发生阶段的小鳞茎中表达较高。参与淀粉合成方向的酶，如ADPG焦磷酸化酶（AGPase）、可溶性淀粉合酶（SSS）、淀粉分支酶（SBE）和颗粒结合淀粉合酶（GBSS）在母鳞片中呈下降趋势，在小鳞茎出现和膨大阶段的小鳞茎中基因表达较高，而在分解方向的酶，淀粉脱支酶（SDBE）在母鳞片中的基因表达高于小鳞茎。
对小鳞茎发育三个阶段的广泛转录组分析为我们在转录水平上理解百合中碳水化合物代谢相关基因提供了大量新信息，并在分子水平上证明了碳水化合物代谢在小鳞茎出现和发育中的基础性。这有助于进一步研究百合及其他相关物种中这些过程的分子机制。
