| Sinosenecio jishouensis is a narrowly restricted species endemic of the Wuling Mountains,with a narrow distribution range and only a few populations distributed in Dehang.S.jishouensis is extremely demanding of habitats and is suitable for warm,moist habitats.Sinosenecio baojingensis is also an endemic species in the Wuling Mountains,its distribution altitude is similar to that of S.jishouensis,and it grows on shady slopes,but the population is sparse.With the global warming,high temperature will inevitably affect their living environment.In this study,we investigated the physiological and molecular effects of high temperature on the growth and development of S.jishouensis and S.baojingensis,and searched for pathways and genes related to high temperature stress to provide a theoretical basis for S.jishouensis and S.baojingensis to to cope with hot weather and protect biodiversity in the Wuling Mountains.The results of the study are as follows:(1)under the 30℃ treatment,the phenotypes of S.jishouensis appeared slightly damaged,while the phenotype of S.baojingensis did not appear damaged;under the35℃ treatment,the leaves of S.jishouensis and S.baojingensis were significantly damaged,which showed that the chlorophyll content further decreased,the total chlorophyll content of S.jishouensis decreased 36.1%,and the total chlorophyll content of S.baojingensis decreased 29.4%;The content of antioxidant enzyme and MDA increased significantly,the content of MDA increased by 9 times in S.jishouensis and5.9 times in S.baojingensis.However,in terms of phenotype,chlorophyll decline and MDA content,the damage degree of S.baojingensis was less than that of S.jishouensis.(2)Under the treatment of 30℃,the net photosynthetic rate of S.jishouensis decreased significantly,while the net photosynthetic rate of S.baojingensis were close to those of the control group;at 35℃,both S.jishouensis and S.baojingensis were severely stressed by high temperature,and their net photosynthetic rate,stomatal conductance,transpiration rate,and Fv/Fm decreased significantly.However,the phenotypic and physiological indicest showed that the degree of damage was less in S.baojingensis than in S.jishouensis.Therefore,we speculate that S.jishouensis is less heat tolerant than S.baojingensis,but both S.jishouensis and S.baojingensis are damaged under the treatment of 35℃.High temperature is an important factor to restrict the distribution of S.jishouensis and S.baojingensis.(3)The transcriptome sequencing of S.jishouensis and S.baojingensis treated by25℃ and 35℃ showed that 1,426 differential genes were generated in S.jishouensis and7,989 differential genes were generated in S.baojingensis after high temperature treatment.After GO functional annotation of these differential genes,it was found that S.jishouensis and S.baojingensis were mainly enriched in metabolic process and transport activity,and after KEGG pathway analysis of these differential genes,it was found that most of the differential genes in S.jishouensis and S.baojingensis were annotated to carbon metabolism,signal transduction,folding and degradation.(4)The transcription factors expressed in S.jishouensis were much lower than in S.baojingensis,and HSF genes associated with heat stress were not expressed in S.jishouensis and were mostly up-regulated in S.baojingensis.After high temperature treatment,14 HSPs genes were differentially expressed in S.jishouensis;after high temperature treatment,39 HSPs genes were differentially expressed in S.baojingensis,most of which were up-regulated.The overexpression of HSPs-related genes may be the reason why S.baojingensis is more heat-resistant than S.jishouensis.In addition,four genes related to HSPs,c193354.graph＿c0,c201144.graph＿c0,c195286.graph＿c0,and c203748.graph＿c0,were co-expressed in S.jishouensist and S.baojingensis,which may be important genes for both to respond to heat stress.In conclusion,S.jishouensis was slightly under high temperature stress at 30℃,and S.jishouensis and S.baojingensis were obviously damaged at 35℃,but the damage degree of S.baojingensis was lower than that of S.jishouensis.High temperature was an important factor limiting the distribution of S.jishouensis and.From the transcriptome,we can know that the high expression of heat shock protein in S.baojingensis may be an important reason why the heat resistance of S.baojingensis is higher than that of S.jishouensis. |
