A Study On The Aging Mechanism Of Metasequoia Glyptostroboides Seeds Based On Transcriptomic Analysis

Metasequoia glyptostroboides seeds have low vigor and rapid loss of vigor,and this may be one of the important reasons for the difficulty in natural regeneration of its native population.However,the physiological mechanism of M.glyptostroboides seed aging is not fully understood.This study explored the physiological mechanism of M.glyptostroboides seed aging through artificial accelerated aging treatment and transcriptomics analysis methods.The main results are as follows:1.The average viability of newly harvested M.glyptostroboides seeds is low.With artificial accelerated aging treatment,seed viability is lost in a reverse“S”shape,and the germination rate is more sensitive to the aging treatment than the germination rate.The initial germination rate of newly harvested M.glyptostroboides seeds was（58.00±8.08）%.Then with the extension of aging time,the germination rate,germination vigor,germination index and vitality index showed roughly the same changing trend.That’s to say,there was no significant difference in the control group after 2 days of aging,and then they decrease significantly as the aging time increased,and the germination rate was almost zero after 8 days of aging.T₅₀ continued to increase significantly after 2 days of aging,and reached the maximum value after 6days of aging,and there was no significant change thereafter.The root length,seedling height and fresh weight of the seeds were not significantly different from the control group after 2,4,and 6 days of aging,and the dry weight was also not significantly different from the control after 2,4 days of aging,and only significantly decreased after 6 days of aging.2.In the artificial accelerated aging process of M.glyptostroboides seeds,the related structure and mechanism（should be mainly mitochondria）seems to be too late to produce and accumulate excessive ROS,which are already disintegrated due to aging damage.Therefore,at the beginning of the aging treatment,the production rate and content of the superoxide anion decreased rapidly,and the activity of antioxidant enzyme SOD also decreased rapidly,and then remained at a low level,so that the H₂O₂content and MDA content did not change significantly during the entire aging process.3.With the extension of aging time,the number of differentially expressed genes gradually decreases,and the number of up-regulated genes is higher than that of down-regulated genes.After 2,4,and 6 days of aging,the pathways with the most significant enrichment of differentially expressed genes are“endoplasmic reticulum protein processing”,“oxidative phosphorylation”and“TCA cycle”.The“endoplasmic reticulum protein processing”pathway involves the differential expression of genes such as ER Man1,Ero,Ubx,RAD23,Png1,PDIs,Sec61,DSK2,and p97.It focuses on the ERAD pathway and actively responds to endoplasmic reticulum stress.M.glyptostroboides seeds developed an endoplasmic reticulum stress response after 2 days of aging.A large number of endoplasmic reticulum stress-related genes such as Bip,CNX and GRP94 were up-regulated;as the aging time further prolonged,DSK2,RAD23,Png1,p97 and other genes were down-regulated,which reduces the efficiency of ERAD.4.Except for the GPX genes,the expression of APX and CAT and other antioxidant enzyme genes and non-enzymatic antioxidant GPX genes are basically consistent with the changes in the corresponding antioxidant enzyme activity and non-enzymatic antioxidant content during the aging process measured above.5.C2H2,NAC and other aging-related transcription factors are mostly up-regulated with aging;Stress-related transcription factors are also mostly up-regulated after 2 days of aging,such as MYB,b ZIP,Trihelix,b HLH,HSF and so on.In summary,the rapid loss of vitality of M.glyptostroboides seeds during artificial accelerated aging is probably mainly related to the rapid disintegration of mitochondria and the ERAD pathway.