Cytokinin signaling pathway involved in 6-BA-induced wound healing in potato tubers

6-Benzylaminopurine (6-BA) can modulate plant resistance to abiotic stress. However, whether 6-BA regulates potato wound healing and the molecular mechanisms involved remain unknown. In this study, the potato tubers were bisected at the equator and immersed in 6-BA (50 mg/L) for healing. The effects of 6-BA on CTK synthesis and signaling and on phenylpropanoid metabolism were then analyzed. The role of StRR1 in suberin polyphenolic (SPP) and lignin synthesis was verified. Weight loss of wounded tubers and the disease index were determined. The results showed that 6-BA increased isopentenyl adenine (iPA) and trans-zeatin (tZ) levels by activating ISOPENTENYL TRANSFERASE (StIPT), and simultaneously inhibiting CYTOKININ OXIDASE/DEHYDROGENASE (StCKX). 6-BA also induced the transcription of HISTIDINE KINASE (StHK),HISTIDINE PHOSPHOTRANSFER (StHP),RESPONSE REGULATOR 1 (StRR1) at wounds of potato tubers. Meanwhile, 6-BA induced PHENYLALAMINE AMMONIA LYASE (StPAL), 4-COUMARATE: COENZYME A LIGASE (St4CL) and CINNAMYL ALCOHOL DEHYDROGENASE (StCAD) expression, leading to an increase in phenylalanine ammonia lyase (PAL), coumarate-CoA ligase (4CL) and cinnamyl alcohol dehydrogenase (CAD) activities. As a result, the synthesis of phenolic acids (cinnamic acid, p-coumaric acid, caffeic acid, and sinapic acid) and lignin monomers (cinnamyl alcohol, coniferyl alcohol, and sinapyl alcohol) was enhanced. Further analysis showed that StRR1 can activate StPAL, St4CL, and StCAD. Overexpression of StRR1 in Nicotiana benthamiana leaves can induce NbPAL, Nb4CL, and NbCAD10, thereby facilitating the accumulation of phenolic acid and lignin monomers. Furthermore, 6-BA accelerated the deposition of SPP and lignin at wounds, ultimately alleviating the weight loss and the disease index. Taken together, 6-BA may facilitate wound healing in potato tubers by stimulating the CTK signaling pathway. The study reveals some of the molecular and physiological mechanisms by which 6-BA promotes wound healing in potato tubers, providing a new alternative strategy for postharvest healing in underground root vegetables.