| Low temperature and low light stress seriously affected the growth,yield and quality of melon crops and the geographical distribution of varieties.Lagenaria siceraria Standl.It belongs to cucurbitaceae.It is often used as grafting rootstock for melon crops because of its good low temperature tolerance,high grafting affinity and little influence on melon quality.In this paper,30 gourd rootstock resources were treated with low temperature and low light stress,and extreme tolerance varieties were screened to explore their physiological and biochemical changes and gene expression differences after 6h of low temperature,low light and low temperature and low light stress.The main results are as follows:1.The chilling damage index of the 30 materials ranged from 0.13-0.95 with an average of 0.40,among which ’P13’ was 0.16 and ’P17’ was 0.7±0.07.Combined with production and application,’P13’ was selected as the material with strong low temperature and low light resistance,and ’P17’ as the material with low temperature and low light sensitivity.2.After low temperature treatment,the leaves of the two cultivars were wilted,Pn,Fv/Fm,ΦPⅡand qP decreased significantly,while the contents of soluble protein and activities of SOD and POD increased significantly.MDA content in P17 was significantly increased,and CAT enzyme activity was significantly decreased,while CAT enzyme activity in P13 was significantly increased.The range of physiological indexes of P13 was smaller than that of P17,which was sensitive to low temperature and low light.Transcriptome sequencing and GO analysis showed that DEGs of the two varieties were mainly enriched in metabolic processes,cellular and catalytic activities.KEGG analysis showed that DEGs were mainly involved in plant hormone signal transduction,starch and sucrose metabolism,and phenylpropyl biosynthesis.The AP2/ERF transcription factor family was the most abundant in the two varieties.64（52 up-regulated and 12 down-regulated）and 78（58 up-regulated and 20 down-regulated）differentially expressed AP2/ERF transcription factors were identified in P13 and P17,respectively.AP2/ERF genes（Lsi09G005960,Lsi05G012660,Lsi08G008230,Lsi02G007760,Lsi04G023820,Lsi07G012820,Lsi11G002400,Lsi10G005230,Lsi06G004690,Lsi08G005640）were co-expressed in the two varieties played a key role in regulating cold stress of calabash rootstock.3.After low light treatment,Pn decreased significantly,intercellular CO2 concentration increased significantly,and chlorophyll fluorescence parameters decreased significantly.SOD and CAT activities of P13 were significantly increased,POD activity was significantly decreased,but SOD and CAT activities of P17 were significantly decreased.The two enrichment pathways mainly focus on photosynthesis,plant hormone signaling and phenylpropyl biosynthesis.The up-regulated expression of photosynthetic pathway related genes in two varieties mainly included Psb P,Psb Q,PsbY,PsbW.psaA,psbB and other proteins.The number and degree of up-regulated genes in P13 were significantly higher than those in P17.The ethylene transcription factors were the most abundant in the two varieties of calabash rootstock.Under low light stress,16 ethylene transcription factor genes that respond to low light play key regulatory roles.4.Under low temperature and low light stress,the leaves of the two calabash varieties withered,the photosynthetic activity was inhibited,and the chlorophyll fluorescence parameters decreased significantly.MDA content,SOD,POD,CAT enzyme activities and soluble protein content of P13 and P17 were significantly increased.The range of physiological indexes of low temperature and low light resistance P13 is smaller than that of low temperature and low light sensitive material P17.The representative pathway of the two varieties was plant hormone signal transduction,and the auxin response or induction protein encoded by DEGs was up-regulated after low temperature and low light treatment.The hormone signaling core gene Lsi07G004940 was identified.Six up-regulated AP2/ERF transcription factor genes（Lsi09G003100,Lsi09G005960,Lsi05G012660,Lsi08G008230,Lsi02G007760,Lsi04G023820）and six down-regulated genes（Lsil0G00523 0,Lsi08G005640,Lsi05G000690,Lsi08G012340,Lsi0 7G012820,Lsi05G018170）were the key genes of common response to low temperature and low light stress.5.The symptoms of cold stress and leaf photosystem damage were more serious in two varieties of calabash under low temperature than under low temperature and low light stress.There were 4384 degscommon between P13 and P7 cultivars under low temperature treatment,786 Degscommon between the two cultivars under low light treatment,and 4384 Degscommon between the two cultivars under low temperature and low light treatment.The total number of differentially expressed genes of calabash varieties under low temperature treatment was higher than that under low temperature and low light treatment.Lsi05G012660,Lsi04G023820,Lsi02G007760and Lsi08G005640 were the key genes responding to low temperature,low light and low light at the same time.The expression levels of these four AP2/ERF transcription factor genes were higher at low temperature than at low temperature and low light. |
