Abstract
BackgroundGynostemma pentaphyllum is an important perennial medicinal herb belonging to the family Cucurbitaceae. Aerial stem-to-rhizome transition before entering the winter is an adaptive regenerative strategy in G. pentaphyllum that enables it to survive during winter. However, the molecular regulation of aerial stem-to-rhizome transition is unknown in plants. Here, integrated transcriptome and miRNA analysis was conducted to investigate the regulatory network of stem-to-rhizome transition.ResultsNine transcriptome libraries prepared from stem/rhizome samples collected at three stages of developmental stem-to-rhizome transition were sequenced and a total of 5428 differentially expressed genes (DEGs) were identified. DEGs associated with gravitropism, cell wall biosynthesis, photoperiod, hormone signaling, and carbohydrate metabolism were found to regulate stem-to-rhizome transition. Nine small RNA libraries were parallelly sequenced, and seven significantly differentially expressed miRNAs (DEMs) were identified, including four known and three novel miRNAs. The seven DEMs targeted 123 mRNAs, and six pairs of miRNA-target showed significantly opposite expression trends. The GpmiR166b-GpECH2 module involved in stem-to-rhizome transition probably promotes cell expansion by IBA-to-IAA conversion, and the GpmiR166e-GpSGT-like module probably protects IAA from degradation, thereby promoting rhizome formation. GpmiR156a was found to be involved in stem-to-rhizome transition by inhibiting the expression of GpSPL13A/GpSPL6, which are believed to negatively regulate vegetative phase transition. GpmiR156a and a novel miRNA Co.47071 co-repressed the expression of growth inhibitor GpRAV-like during stem-to-rhizome transition. These miRNAs and their targets were first reported to be involved in the formation of rhizomes. In this study, the expression patterns of DEGs, DEMs and their targets were further validated by quantitative real-time PCR, supporting the reliability of sequencing data.ConclusionsOur study revealed a comprehensive molecular network regulating the transition of aerial stem to rhizome in G. pentaphyllum. These results broaden our understanding of developmental phase transitions in plants.
Highlights
Gynostemma pentaphyllum is an important perennial medicinal herb belonging to the family Cucurbitaceae
Morphological and histological traits of aerial stem-torhizome transition in G. pentaphyllum As shown in Fig. 1, aerial stem, aboveground moderately swelling stem, and underground newly formed rhizome were selected as representative stages of developmental aerial stem-to-rhizome transition in G. pentaphyllum and were named stage 1, stage 2, and stage 3, respectively
Transcriptomic analysis reveals the important roles of differentially expressed genes (DEGs) involved in G. pentaphyllum aerial stem-to-rhizome transition RNA-Seq is a powerful and efficient means to discover putative functional genes involved in diverse biological processes, especially for plant species without a reference genome [10]
Summary
Gynostemma pentaphyllum is an important perennial medicinal herb belonging to the family Cucurbitaceae. G. pentaphyllum contains important medicinal components, called gypenosides, which are reportedly effective in the treatment of various illnesses, such as inflammation, cardiovascular diseases, and cancer [2,3,4] This herb is widely used as tea or functional food [5], and has received substantial attention in recent years. Before entering the winter, the subapical regions of some aerial stems swell and drill into the soil to form rhizomes that produce new plants in the year [6]. This vegetative regeneration is an adaptation of G. pentaphyllum to the natural environment to maintain its population. This developmental phase transition is an interesting research topic in the field of developmental biology
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