Dynamic Characteristics And Gene Expression Analysis Of Tuber Formation In Dioscorea Alata L.

Water yam(Dioscorea alata L.)is an annual or perennial herbaceous vine with monocotyledon twining.It is widely planted in southern China.The main product organ of water yam is the underground tuber,which has the characteristics of high protein,high potassium and low fiber.It is rich in nutrition and can be used as vegetable and medicine.The formation and expansion of plant tubers is a complex physiological process,involving a series of things such as morphogenesis,material accumulation,metabolic regulation and so on.There are some problems in production,such as delayed expansion,short expansion period,insufficient maturity and storage difficulties caused by high temperature in summer.However,previous studies mainly focused on Dioscorea opposita,but the morphological characteristics,cell and physiological basis of tuber formation of water yam have not been clarified.In this experiment,the tubers from different growth stages were sampled regularly to determine their morphological and physiological indexes,and transcriptome sequencing was used to systematically analyze the differentially expressed genes during the tuber growth and development.In order to analyze the physiological basis and key gene expression characteristics of yam tuber formation,provide theoretical basis for revealing the tuber formation mechanism,quality improvement and efficient cultivation regulation.The main results are as follows:1.Morphological development and anatomical observation of tubers.The tuber volume,fresh weight and dry weight were measured at 10,20,30,40,50 and 60 days after tuber expansion,the internal structure was observed by paraffin section.The changes of cortex thickness and cell size in different periods were compared.It was found that the tuber of water yam in Nanjing area was in the peak period from the end of September to the beginning of October.2.Dynamic analysis of nutrient components in tubers.The soluble protein content was higher in the early stage of tuber formation,and decreased in the later growth stage;the total starch content first increased and then decreased in the later stage of tuber formation;the polysaccharide content first increased and then reached the peak value on the 20th day,then decreased gradually;the soluble total sugar increased in a fluctuating manner with the tuber expansion,and reached the maximum value after 40 days of tuber expansion.3.Dynamic detection of hormone content in tuber.The results showed that the contents of IAA and KT were lower,IAA reached the maximum after 30 days of tuber expansion;KT had no significant difference;ABA content was smaller at the initial stage of tuber expansion,and the acceleration rate began to accelerate significantly at 20 days of tuber expansion.The content of GA3 was very high at the beginning of tuber expansion,and decreased rapidly to a lower level without any change;the content of JA was higher,reached the maximum at 30 days of expansion,and decreased to the lowest level at the later stage of expansion.4.Gene expression analysis of tuber development.A total of 186793 transcripts and 42042 unigenes were obtained from different growth stages of yam tubers.The number of genes expressed at the initial stage of tuber is the most,which is an important stage of tuber development;the initial stage of expansion involves the signal transduction of multiple hormones.The expression of genes related to starch synthesis was consistent with tuber expansion,and the highest synthesis efficiency was achieved at the peak stage of tuber expansion,modification processing and secondary metabolite synthesis were carried out in the later stage.Using DaActin as the internal reference gene,eight genes were selected for RT-qPCR verification.The analysis results showed that the expression pattern of DEGs selected was consistent with that of RNA-seq analysis.