Physiological Response And Differentially Expressed Genes Analysis Of Pitaya Under Cold Stress

Pitaya(Hylocereus undulatus Britt.)is a tropical fruit belonging to Hylocereus undatus.And have poorly resistance to cold.The young issues such as bud and spray are extremely vulnerable to frostbite when the temperature is lower than 5 ? in winter or later spring's cold spell,which affecting the growth and yield of the pitaya.The content of chlorophyll,water,REC,MDA,soluble sugar,soluble protein,proline and antioxidant system wre measured to study the cold resistance physiological mechanism of seedling and cutting seedling of Pitayais 'Guangming 2'.Through which we analysed the cold tolerance of Pitaya plants in physiological mechanism.And we also looked out the suitable calcium concentration to reduce cold indure.To analyze the different expressed genes of Pitayais under low temperature stress,transcriptome sequencing were used to get the transcriptome data of pitaya under-2? and normal temperature.130264 Unigenes were found,among which 2154 genes were expressed differentially.Then we studied the molecula responsing function under cold stress through functional and metabolic pathway annotation and difference enrichment analysis.Results are mainly as follows:1.After recovering growth of 24 hours,'Guangming 2' Pitaya plants which exposed to cold stress have showed chilling injury symptoms,such as chlorosis,rusting,hygrophanous,wilting,soft rot and death.36 hours,cold stress of 5? would not cause the death of pitaya.But when temperature were declined at-2 ? and-5 ?,12 hours would enoughly cause a mass death of plants.Low temperature decreased the water and chlorophyll content and damaged biofilm stability,changed the content of osmoregulation substance of'Guangming 2' plants.The electrolyte leakage rates of seeding and cutting seedlings have reached the hightest value at the first 12 h.And the stress temperature above 0 ? made a larger growth of electrolyte leakage rates than that of under 0 ? with the lasting of time.The free proline increased rapidly in the earlier stage of cold stress,and reached the peak at 24 h.The MDA value increased with the extension of stress time and the decrease of temperature.Soluble sugar and soluble protein content also showed upward trends.Cold stress promoted antioxidant enzyme activity of 'Guangming 2' pitaya.2.-2 ? is a critical temperature of cold stress for 'Guangming 2'.The soluble protein peaks of both seedlings and cutting seedlings were appeared at-2 ?.With the extension of stress time,the REC growth rates under-2 ? and-5 ? were smaller than that of under 5 ? and 0 ?.The changes of MDA content were not significant within time,and there were also no obvious differences in stem water content between these two temperatures.The content of Pro was negatively correlated with temperature when it was upon-2 ?,but the regularity is not strong when temperature was lower than-2?.3.The calcium concentration of 10 and 15 mmol·L-1 could reduce the cold damage of pitaya within 36 hours under-2 ? low temperature.The water content,chlorophyll content,soluble protein and free proline content of stem were significantly higher than that of control,and the exudation rate and MDA content of stem were observably lower.4.In the transcriptome data of 'Guangming 2',we found that there were more up-regulated genes(1141)than down-regulated genes(1073)between room temperature and-2 ? after 48 hours' cold stress.Though annotationing of KOG we found large differences occurring in the common functions,protein modification and transformation,protein partner,signal transduction mechanism,transcription,the structure of the ribosome and biological variety.GO analysis showed that there were different genes enrichments in synthesis,metabolism and enzyme activity tempers.KEGG analysis found that a large amount of different expressing genes were appearing in the pathways of photosynthesis and metabolic.All those showed that Pitaya having a complex metabolic and enzymatic reaction to response to cold damage.5.The expression of genes wre optimaly selected under low temperature.Through qRT-PCR,we founded the trends of Pitaya' genes expression under cold stress were various,such as FAD,LTI,ICE1 and ZAT12,but all were in favor of decreasing the injury at low temperature in the first 24 h of stress.The stress more than 36 h,ICE1 gene expression downregulating,ZAT12 expression increasing would cause be inhibited of CBF pathway,and bring about the weaking response to low temperatures of the downstream CORs genes such as LTI.The result showed that the body's resistance to cold was cut down,the water loss was aggravated,ROS could not be cleaned in time,metabolic was disordered.Thus,the Pro content,activity of SOD and POD were sharply reduced at 36 h of stress.