Effects of shading on tuberous root traits, photosynthetic characteristics and gene transcription of Rehmannia glutinosa / 中草药

ABSTRACT

To reveal the effects of shading on tuberous root and photosynthetic characteristics of Rehmannia glutinosa, and analyze the molecular mechanism of shading affecting the expansion of R. glutinosa tuberous root by transcriptome sequencing. Methods: R. glutinosa plants were treated with full light, 60% shading and 90% shading. High-throughput sequencing was used to sequence the transcriptome of the R. glutinosa tuberous roots treated with full-light and 90% shading, and the differentially expressed genes were screened out. The expression characteristics of some genes in tuberous roots and leaves were analyzed by real-time fluorescence quantitative PCR. Results: After shading, the number of parenchyma cell layers in the tuberous roots was decreased, but the proportion of ducts was increased, the length, diameter and fresh weight of tuberous roots were decreased significantly, and the tuberous roots barely expanded under 90% shading treatment. The number of parenchyma cell was decreased and the proportion of duct was increased in root tubers of R. glutinosa. With the increase of shading degree, the content of chlorophyll a and b and total chlorophyll content were gradually decreased, and photosynthetic capacity was decreased. A total of 3 348 differentially expressed genes were obtained by transcriptome analysis, of which 1 396 were down-regulated and 1 952 were up-regulated. Through enrichment analysis of KEGG metabolic pathway, 1 668 differentially expressed genes (53.4%) were enriched into 117 metabolic pathways, and 17 of them were significantly enriched pathways. The plant hormone signaling pathway was enriched firstly, followed by the plant pathogen interaction pathway, the phenylethanoid glycoside biosynthesis pathway, starch and sucrose metabolic pathways were also enriched significantly. In the hormone signaling pathway, most of different expressed genes were up-regulated. Eleven expansin genes were down-regulated under 90% shading, only five expansin genes were up-regulated. Two of beta-amylase genes (Bmy) related to starch degradation were up-regulated when shading treated, while the sucrose phosphate synthase genes (SPS) were down-regulated. Most of the genes involved in lignin synthesis were down-regulated and most of the genes involved in cellulose synthesis were up-regulated. Conclusion: The photosynthetic capacity of R. glutinosa was decreased under shading conditions, and led to the accumulation of photosynthate decreased in its leaf and tuberous root. R. glutinosa plant responded to shading by regulating the differential expression of a series of hormone pathway genes, which prevent the expansion of tuberous roots.