Analysis Of Senescence Mechanism In Picea Mongolica

Picea mongolica（H.Q.Wu）W.D.Xu),an endemic and rare tree species in Inner Mongolia,is a valuable biogenetic resource.According to the sampling survey of Picea mongolica stand,the phenomenon of hollow or rotten tree trunks appeared in individuals about 100 years,which seriously threatens the safety of Picea mongolica forest resources and the health and stability of the Picea mongolica forest ecosystem.Therefore,in our study,Picea mongolica in different ages were taken as the research object,through the growth and development,vascular cambium microstructure,physiological characteristics and transcriptional regulation study at multilevel research,analyze the senescence mechanism in Picea mongolica.It will lay a theoretical foundation for delaying senescence,molecular breeding,resource protection and rational utilization of Picea mongolica.The results show that:（1）According to the analysis of the age group structure of Picea mongolica forest,there are more individuals over the near-mature age than the middle-aged and juvenile individuals,indicating that the Picea mongolica forest has entered the mature stage;with the growth of tree age group,both the trunk diameter at breast height and the growth of tree height decrease,showing a significant negative correlation between tree growth and development.Individual of Picea mongolica about 120 age appeared hollow or decay,it indicated that the age group structure of Picea mongolica stand was mature and showed a declining trend.（2）In the study of the radial increment of Picea mongolica with different ages and the microstructure of the vascular cambium,the analysis of the radial growth of the trunk shows that the daily radial growth of the trunk decreases with the increase of age,and the season radial growth of trunk growth（June,July,August）also decreased with age;anatomical analysis of the vascular cambium showed that the thickness of the vascular cambium and the number of cell layers decreased with age.（3）The physiological characteristics of Picea mongolica of different ages were measured,we found that the net photosynthetic rate（Pn）,transpiration rate（Tr）and water utilization rate（WUE）of photosynthetic characteristics decreased with the increase of age,the intercellular CO₂concentration（Ci）increased with the increase of age,and although the stomatal conductance also increased with the age,the change is not obvious.Besides,net photosynthetic rate,water utilization rate and age were significantly negatively correlated,transpiration rate and stomatal conductance were negatively correlated with age,and intercellular CO₂concentration was significantly positively correlated with age.The content of ABA and SA decreased with the increase of age,and ABA,IAA and SA were significantly different among different ages.（4）A total of 838 significantly differentially expressed genes were obtained from the mRNA sequencing analysis of the vascular cambium of Picea mongolica with different ages.GO was mainly enriched in the photosystem,various stresses,and photosynthesis.KEGG was mainly enriched in photosynthesis and endoplasmic reticulum protein processing pathways;moreover,there were 6 genes in cell catabolism and cell wall annotation,the 5 genes in hormone-related genes,the 6 genes in photosynthesis annotation,stress.The 10 genes in the annotation and defense response annotation showed a trend expression with the increase of tree age;senescence-related transcription factors WRKY50,WRKY28,WRKY57,TCP4,MYB4,MYB123 showed a trend expression with the increase of age.Analysis of senescence-related transcription factor interactions revealed that MYB4has multiple interactions with other proteins.AP2 interacts with multiple transcription factors such as TCP4,b ZIP19,WRKY28,and WRKY57.It indicated that these genes were involved in the aging process of Picea mongolica and played an important regulatory role.（5）A total of 581 known miRNAs were obtained from the vascular cambium miRNA sequencing analysis of different ages,which were distributed in 67 families,of which mi R159 had the largest number of members.There were 42 differentially expressed miRNAs,among 18 differentially expressed miRNAs were highly expressed in 20 age and120 age in 200 age,and 13 differentially expressed miRNAs in 20 age and 120 age and200 age;the 11 were related to development and senescence.The related miRNAs showed a trend of expression with the increase of age.This indicates that these miRNAs have important regulatory roles in the aging process of Picea mongolica;the 33,967 known miRNA target genes were predicted,and the target genes of differential miRNAs GO and KEGG mainly enriched in molecular functions,biological processes,binding,metabolic processes,plant-pathogen interaction,selenocompound metabolism and phenylpropane biosynthesis.（6）Through mRNA and miRNA association analysis,the 6 differentially miRNA target genes were predicted to be involved in phytohormone signaling pathway,the 11differentially miRNA target genes were predicted to be involved in defense response signaling pathway,and the 7 differentially miRNA target genes were predicted to be in the autophagy pathway;the 11 miRNAs related to development and aging were screened for target gene analysis,and it was found that the 6 differential miRNAs targeted to aging and disease resistance-related MA＿96853g0010（Myb＿DNA-binding）,MA＿52440g0010（TCP4）,MA＿124608g0010（NB-ARC）,MA＿728287g0010（NB-ARC）,MA＿290659g0010（HLH36）transcription factor family.Both these miRNAs and corresponding target genes showed a trending expression pattern with age.This indicates that it plays a key regulatory role in the aging process of Picea mongolica in different ages.