Promotion Of Potato Tuber Wound Healing By Hot Water Treatment And Its MYB Transcription Regulation Mechanism

Wound healing is an important postharvest characteristic of potato,but it spends a long time on natural healing.In this study,potato tubers“cv.Longshu No.7”were damaged,and dipped in 45^oC hot water for 10 min,then placed under dark conditions at room temperature（20-25^oC,RH 70-80%）for healing.The weight loss and disease index of potato tubers were measured during healing,the deposition of suberin and lignin in the wound were observed,and the activities of key enzymes and products of phenylpropane metabolism were determined.On the basis of hot water treatment,the key MYB transcription factors involved in tuber wound healing and their mechanism were identified by transcriptome analysis,dual-luciferase assay and yeast one-hybrid test,and their function in suberin formation were verified.The main results are as follows:1.Hot water treatment accelerated the deposition of suberin and lignin in the wound,and effectively reduced weight loss and disease index of damaged tubers during healing.Hot water treatment significantly promoted the expression of StPAL1 and St4CL genes in the wound of potato tuber during healing,increased the activities of PAL and 4CL,and increased the contents of total phenols,flavonoids and lignin.In addition,hot water treatment significantly increased H₂O₂ content and POD activity in tuber wounds.2.Based on the transcriptome data,four candidate MYB transcription factors（MYB168/144/24/48）that may be involved in potato tuber wound healing were screened.The evolutionary analysis showed that they had high homology with MYB transcription factors involved in phenylpropane metabolism,suberin synthesis and lignin metabolism in other species.In addition,three key genes of phenylpropane metabolism,StPAL1,StPAL3and St4CL were screened.All of them contain MYB binding elements in the promoters,indicating that they may be downstream target genes regulated by MYB in tuber wound healing.3.Dual-luciferase assay showed that MYB168 significantly enhanced the promoter activity of StPAL1,StPAL3 and St4CL,which were up-regulated by 3.70,4.93,5.76 times,respectively.On the contrary,MYB144/24/48 had no significant effect on the activity of the above promoters.Yeast one-hybrid test showed that MYB168 could directly bind to the promoter of wound healing target genes StPAL and St4CL,thus enhancing its activity.4.The results of subcellular localization showed that MYB168 was located in the nucleus.Overexpression of MYB168 in Nicotiana.benthamian leaves could significantly promote the synthesis of phenolic acids monomers such as caffeic acid,sinapic acid,cinnamic acid,and lignin monomers such as sinapyl alcohol,coniferyl alcohol and cinnamyl alcohol in N.benthamian leaves.In addition,overexpression of MYB168 also promoted the deposition of suberin poly phenolic in N.benthamian leaves.To sum up,hot water treatment can accelerate the deposition of suberin and lignin in the wound and promote the wound healing of potato tubers by activating phenylpropane metabolism,increasing H₂O₂ content and peroxidase activity.MYB168 can directly bind and activate the promoters of StPAL and St4CL,enhance the expression of StPAL and St4CL genes,accelerate the synthesis of phenolic acid monomers and the deposition of suberin poly phenolic.