Comparative transcription profiles reveal that carbohydrates and hormone signalling pathways mediate flower induction in Juglans sigillata after girdling

Flower induction in iron walnut (Juglans sigillata) is a complex and highly regulated process involving multiple signal pathways to ensure flower bud formation in the subsequent year. However, the underlying molecular mechanism of the induction remains unknown. Girdling is an effective method for inducing flower bud formation in iron walnut. In this study, comparative transcriptome profiles between girdled (G) and ungirdled (unG) materials on the same tree were used to identify the signal pathway involved in flower bud induction by girdling in iron walnut. The results showed that genes related to starch and carbohydrate metabolism, photosynthesis, and hormone signals, including pectinesterase (PAE), trehalose 6-photosphatase (TPP), α-aminolase (α-AL), atpF, and auxin response factor ARF9, participated in the induction process after girdling. Expression pattern of genes related to sugar metabolism revealed that sugar was the initial signal for flower induction and that photosynthesis increased after girdling, influenced by the carbon source–sink relationship. Hormone signalling networks including auxin, abscisic acid (ABA), and brassinolide also contributed to flower bud induction of iron walnut. Auxin played an important role in tissue regeneration and flower induction after girdling. ABA directly participated in flower induction. Gene expression pattern similarities between ABA and sugar metabolism signals indicated that ABA may also be involved in sugar regulation, in turn regulating floral induction. In summary, flower induction after girdling in iron walnut is mainly regulated by a polygenic network centred on sugar and hormone signals.