Petiole hormones act as regulators in the early phototropic leaf movements of grape (Vitis vinifera L.) revealed by comparative transcriptome profiling

Abstract Phototropism is of great importance in orienting their photosynthetic organs towards the light so as to optimize the light capture capacity of the aerial parts in seedlings of higher plants. Approximately 20-day-old grape (Vitis vinifera L.) leaves were the fastest in response to phototropism. However, the molecular network and genetic regulatory mechanisms that govern phototropism in grape leaves remained elusive. Leave blades and petioles were sampled from shoots of V. vinifera cv. ‘Italian Riesling’ trees that were artificially fixed on the wire with strings under the condition of the blade abaxial side face-upward in the field (fixation of shoots did not interfere with leaves rotation), respectively. Leaves growing in the natural state (not artificially fixed on the wire) as control. The treated blades rotate from the abaxial side to the adaxial side after fixation for 2 h, and the phototropic response was completed after 6–10 hours. The endogenous hormone concentrations were measured from the time series in blades and petioles. After irradiating the abaxial side of treated blades for 3 h, leaves were sampled for RNA sequencing analysis. Here, the results of endogenous hormone concentrations showed that phototropic response was beneficial to increase IAA content in blades and petioles, but had opposite effect on GA content. The contents of ZT and ABA in treated petioles were considerably higher than those of control during the phototropic response. A total number of 181 and 1,810 differentially expressed genes (DEGs) were identified in blades and petioles, respectively. KEGG enrichment analysis showed that DEGs involved in the hormone signal transduction pathway were significantly enriched in petioles. A total of 44 genes involved in the hormone signalling pathways of auxin, CTK, GA, ABA, ethylene (ETH), BR, jasmonic acid (JA) and salicylic acid (SA), including 32 up-regulated and 12 down-regulated genes. In addition, the expression of key transcription factors (TFs) and candidate genes, including HY5, AUX1, AUX/IAA, SAUR, HP3, ARR9, BKI1, PP2C8, ABI5 and PIF3, were responsible for grape leaf phototropism. In conclusion, our study provides an initial understanding of the response of petiole hormones to phototropic leaf movements in grape, and also provides possible candidate genes involved in grape leaf phototropism that could be used to guide future efforts in this field.