Key Laboratory of Plant Resources and China National Botanical Garden, Institute of Botany, Chinese Academy of Sciences, Beijing, Xiangshan, 100093, China.
BMC Plant Biol. 2022 Aug 27;22(1):415. doi: 10.1186/s12870-022-03801-8.
Aerial bulbils are important vegetative reproductive organs in Lilium. They are often perpetually dormant in most Lilium species, and little is known about the induction of these vegetative structures. The world-famous Oriental hybrid lily cultivar 'Sorbonne', which blooms naturally devoid of aerial bulbils, is known for its lovely appearance and sweet fragrance. We found that decapitation stimulated the outgrowth of aerial bulbils at lower stems (LSs) and then application of low and high concentrations of IAA promoted aerial bulbils emergence around the wound at upper stems (USs) of 'Sorbonne'. However, the genetic basis of aerial bulbil induction is still unclear. Herein, 'Sorbonne' transcriptome has been sequenced for the first time using the combination of third-generation long-read and next-generation short-read technology. A total of 46,557 high-quality non-redundant full-length transcripts were generated. Transcriptomic profiling was performed on seven tissues and stems with treatments of decapitation and application of low and high concentrations of IAA, respectively. Functional annotation of 1918 DEGs within stem samples of different treatments showed that hormone signaling, sugar metabolism and wound-induced genes were crucial to bulbils outgrowth. The expression pattern of auxin-, shoot branching hormone-, plant defense hormone- and wound-inducing-related genes indicated their crucial roles in bulbil induction. Then we established five hormone- and wounding-regulated co-expression modules and identified some candidate transcriptional factors, such as MYB, bZIP, and bHLH, that may function in inducing bulbils. High connectivity was observed among hormone signaling genes, wound-induced genes, and some transcriptional factors, suggesting wound- and hormone-invoked signals exhibit extensive cross-talk and regulate bulbil initiation-associated genes via multilayered regulatory cascades. We propose that the induction of aerial bulbils at LSs after decapitation can be explained as the release of apical dominance. In contrast, the induction of aerial bulbils at the cut surface of USs after IAA application occurs via a process similar to callus formation. This study provides abundant candidate genes that will deepen our understanding of the regulation of bulbil outgrowth, paving the way for further molecular breeding of lily.
气生鳞茎是百合属植物重要的营养繁殖器官。大多数百合物种中的气生鳞茎通常处于持续休眠状态，对这些营养结构的诱导知之甚少。世界著名的东方杂种百合品种‘索邦’自然开花时没有气生鳞茎，因其可爱的外观和甜美的香气而闻名。我们发现，去顶刺激了下部茎（LS）上气生鳞茎的生长，然后应用低浓度和高浓度的 IAA 促进了‘索邦’上部茎（US）伤口周围气生鳞茎的萌发。然而，气生鳞茎诱导的遗传基础仍不清楚。在此，我们首次使用第三代长读长和下一代短读长技术组合对‘索邦’进行了转录组测序。共产生了 46557 个高质量的非冗余全长转录本。分别对 7 种组织和不同处理的茎进行转录组分析，包括去顶、低浓度和高浓度 IAA 处理。不同处理茎样本中 1918 个差异表达基因（DEGs）的功能注释表明，激素信号、糖代谢和伤诱导基因对鳞茎的生长至关重要。激素、分枝激素、植物防御激素和伤诱导相关基因的表达模式表明它们在鳞茎诱导中的关键作用。然后我们建立了五个激素和伤调节的共表达模块，并鉴定了一些候选转录因子，如 MYB、bZIP 和 bHLH，它们可能在诱导鳞茎中发挥作用。激素信号基因、伤诱导基因和一些转录因子之间存在高度的连通性，表明伤和激素诱导的信号表现出广泛的相互作用，并通过多层次的调控级联调节与鳞茎起始相关的基因。我们提出，去顶后 LS 上气生鳞茎的诱导可以解释为顶端优势的释放。相反，IAA 处理后 US 切口表面上气生鳞茎的诱导是通过类似于愈伤组织形成的过程发生的。本研究提供了丰富的候选基因，将加深我们对鳞茎生长调控的理解，为百合的进一步分子育种铺平道路。
