Transcription profiles reveal the regulatory mechanisms of spur bud changes and flower induction in response to shoot bending in apple (Malus domestica Borkh.)
Shoot bending, as an effective agronomic measure, has been widely used to promote flowering in ‘Fuji’ apple trees. Here, we examined the transcriptional responses of genes in ‘Fuji’ apple buds at different flowering stages under a shoot-bending treatment using RNA sequencing. A complex genetic crosstalk-regulated network, involving abscisic acid-related genes, starch metabolism and circadian rhythm-related genes, as well as stress response-related genes, was up-regulated by shoot bending, in which were contrbuted to apple flower bud formation in response to shoot-bending conditions.
Flower induction plays an important role in the apple tree life cycle, but young trees produce fewer and inferior flower buds. Shoot bending, as an effective agronomic measure, has been widely used to promote flowering in ‘Fuji’ apple trees. However, little is known about the gene expression network patterns and molecular regulatory mechanisms caused by shoot bending during the induced flowering. Here, we examined the transcriptional responses of genes in ‘Fuji’ apple buds at different flowering stages under a shoot-bending treatment using RNA sequencing. A steady up-regulation of carbon metabolism-related genes led to relatively high levels of sucrose in early induced flowering stages and starch accumulation during shoot bending. Additionally, global gene expression profiling determined that cytokinin, indole-3-acetic acid, gibberellin synthesis and signalling-related genes were significantly regulated by shoot bending, contributing to cell division and differentiation, bud growth and flower induction. A complex genetic crosstalk-regulated network, involving abscisic acid-related genes, starch metabolism- and circadian rhythm-related genes, as well as stress response-related genes, was up-regulated by shoot bending. Additionally, some transcription factor family genes that were involved in sugar, abscisic acid and stress response signalling were significantly induced by shoot bending. These important flowering genes, which were mainly involved in photoperiod, age and autonomous pathways, were up-regulated by shoot bending. Thus, a complex genetic network of regulatory mechanisms involved in sugar, hormone and stress response signalling pathways may mediate the induction of apple tree flowering in response to shoot-bending conditions.
KeywordsShoot bending RNA-seq Hormones Sugar Stress response Flower induction ‘Nagafu No. 2’ apple trees
This work was financially supported by National Natural Science Foundation of China (31701664), Science and Technology Innovative Engineering Project in the Shaanxi province of China (2017ZDXM-NY-017).
The project was designed and conceived by LX, JZ and MH. The experimental work was carried out by LX, DZ, MH, CZ and NA. LX, XC, YL and SQ analyzed the data. LX wrote the paper. All authors have read and approved the final version of this manuscript.
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