Comparative transcriptomic analysis of Rosa sterilis inflorescence branches with different trichome types reveals an R3-MYB transcription factor that negatively regulates trichome formation

Rosa sterilis S. D. Shi is an important economic tree in China that produces fruits with high nutritional and medicinal value. Many of R. sterilis' organs are covered with different types of trichomes or prickles that directly affect fruit appearance and plant management. In this study, the transcriptomes of two parts of the inflorescence branch—namely inflorescence stems with flagellated trichomes and pedicels with both flagellated and glandular trichomes were analyzed using RNA sequencing technology. Comparative transcriptomic analysis showed that a large number of transcription factors (TFs) could be involved in the formation and development of trichomes. The accumulation of RsETC1, a TF of the R3-MYB family, was significantly higher in inflorescence stems compared to pedicels; quantitative reverse transcription PCR (qRT-PCR) verified that its expression was significantly higher in inflorescence stems than in pedicels during the first three stages of development, indicating its inhibitory action on the initiation of glandular trichomes in R. sterilis. Moreover, the mRNA level of RsETC1 in trichomeless tissues accumulated to significantly higher levels than in tissues with trichromes, suggesting that this gene may inhibit the formation of trichomes in R. sterilis. Furthermore, over-expression of RsETC1 in Arabidopsis resulted in glabrous phenotypes, and the expression of trichome-related endogenous genes, except for TTG1, was markedly reduced. In addition, the contents of the phytohormones jasmonic acid (JA), gibberellin A3 (GA3), and cytokinins (CKs) in pedicels were significantly higher than those in inflorescence stems, and the expression patterns of the genes related to hormone biosynthesis and signal transduction presented according responses, suggesting that the transduction of these hormones might be crucial for trichome initiation and development. These data provide a new perspective for revealing the molecular mechanism of trichome formation in this species.