The Effect Of Rain-protected Cultivation On Photosynthetic Characteristics, Fruit Development And Related Gene Expression Of Cherries

Cherry（Cerasus pseudocerasus Lindl.）is popular among the public because of its rich fruit,juicy and shape.In recent years,it has been widely grown in Southwest China.However,from flowering to fruit ripening,the whole development stage of cherry will be affected by extreme adverse weather such as"late spring cold",hail and rainstorm.In order to avoid the serious influence of the extreme adverse weather on the yield of cherry under the traditional cultivation mode,the rain-shelter cultivation facilities are recommended.However,under the condition of low solar radiation in Southwest China,rain-shelter cultivation is bound to reduce the photosynthetically active radiation（PAR）.Up to now,the adaptation mechanism of physiological and molecular in cherry to low light under rain-shelter cultivation is still unclear.In the current study,the main cherry cultivar’Manaohong’in Guizhou Province was used as the material to observe the leaf structure,photosynthetic characteristics,antioxidant capacity,fruit setting rate,yield and quality etc.The RNA-Seq and SMRT sequencing technology were used to obtain the key genes in the metabolic pathway related to the response of leaves and fruits to the changes of micro-environment.1)The characteristics of leaves and branches were significantly affected by rain- shelter condition.Compared with the shelter-free,the characteristics of leaf and the growth characteristics of branches in’Manaohong’cherry under rain-shelter condituions had been obvioursly affected.Compared with that under the control conditions,at the 55days after flowering（DAF）（DAF55）,the leaf area under 2a-shelter and 1a-shelter conditions significantly increased by 26.87%and 23.00%,respectively,the change of specific leaf weight was not significant,the length of 2a-shelter and 1a-shelter branches increased,the length of branches internode shortened and had no significant change in shoots diameter.Compared with the shelter-free,the thickness of 2a-shelter and 1a-shelter leaves decreased by 17.67%and 19.70%,respectively,among them,palisade tissue decreased by 18.17%and 15.10%,sponge tissue thickness decreased by 21.09%and 19.07%.There was no significant difference in leaves area and thickness between2a-shelter and 1a-shelter.2)The effect of rain-shelter condition on photosynthetic characteristics of cherry.The measurement results of pigment showed that both the 2a-shelter and 1a-shelter could significantly increase the content of chlorophyll（Chla and Chlb）and carotenoid（Car）in per unit mass of leaves in cherry leaf.At DAF55,the contents of Chla,chlb and Car in 2a-shelter leaves increased by 25.00%,40.35%and 33.33%respectively,which was beneficial to enhance the utilization of low light in the leaves under the rain-shelter cultivation facilities.Notebly,the results of photosynthetic characteristics showed that compared with the shelter-free,the diurnal photosynthetic characteristics of 1a-shelters and 2a-shelters have changed,showing the atypical‘single peak’characteristics,and typical phenomenon of‘noon-slump’pattern was disappeared,therefore,the accumulation of total photosynthesis increased in leaves during the cultivation of rain-shelter leaves.The apparent quantum efficiency（AQY）increased,the light compensation point（LCP）decreased,the apparent carboxylation efficiency（ACE）increased and the carbon dioxide compensation point（CCP）decreased in rain-shelter leaves.These indicated that the cherry leaves could enhance the utilization of low light and CO₂ by changing photosynthetic characteristics,thus increasing the synthesis and accumulation of photosynthetic products.The effect of rain-shelter condition on cherry fruit yield and quality.3)The effect of rain-shelter condition on yield and quality of cherry.The observation of two consecutive years showed that the fruit phenological period would not be affected by the rain-shelter cultivation.Compared with the shelter-free,the fruit size and single fruit weight increased significantly under the rain-shelter condition,and the largest single fruit in 2a-shelter fruit was 6.75 g.In 2a-shelter and1a-shelter fruits,the content of total soluble solids（TSSs）was 12.61%and 12.40%,the content of soluble sugars（SSs）was 10.59%and 10.52%,and the content of ascorbic acid（As A）increased to 9.69 mg/100 g and 8.21 mg/100 g,respectively,they were higher than shelter-free ones.However,the content of TA was not significantly changed.The rate of fruit cracking decreased from 95.00%in the shelter-free to about 4.00%（2a-shelter and 1a-shelter）,and the yield increased significantly,therefore,the yield of’Mnaohong’cherry can be significantly improved by rain-shelter condition,and the fruit quality will not be negatively affected.4)The adaptive regulation mechanism of cherry leaves in rain-shelter condition.Combination of Illumina Hi Seq and single-molecule real-time sequencing（SMRT）technology,6,911 differentially expressed genes（DEGs）were identified in the three stages of cherry fruit development;the DEGs in cherry leaves were mainly enriched in photosynthetic characteristics,photosynthetic pigment synthesis,antioxidant capacity and other metabolic pathways,which in photosynthesisantenna proteins（ko00196）,photosynthesis（ko00195）and carbon fixation in photosynthetic organisms（ko00710）.Compared with the leaves in shelter-free,such as those encoding photosynthetic-antenna proteins（Lhca and Lhcb）,photosynthetic electron transporters（Psb P,Psb R,Psb Y,and Pet F）and carbon fixed genes（rbc L and rbc S）were up-regulated following the application of rain-shelter condition;the transcription levels of genes involved in chlorophyll（hem A,hem N,and chl H）and carotenoidsynthesis（crt B,PDS,crt ISO,and lcy B）in the sheltered leaves were up-regulated and peaked earlier than those in the unsheltered leaves,thereby promoting organic matter accumulation in leaves.Metabolic pathways related to antioxidant capacity of leaves,such as peroxisome（ko04146）,phenylpropanoid biosynthesis（ko00940）,glutathione metabolism（ko00053）and carotenoid biosynthesis（ko00906）pathways.Among them,the transcription level of several key genes in metabolic pathway was enhanced in the leaves of shelter cultivation,which was conducive to the ability of the leaves to clear ROS,thus maintaining the photosynthetic efficiency of the leaves in the sheltered.5)The adaptive regulation mechanism of cherry fruits in rain-shelter condition.During the three development stage of cherry fruit,1,755 DEGs were identified in fruits between rain-shelter and shelter-free.Compared the differential expressed genes in rain-shelter and shelter-free,we found that they were mainly enriched in sugar synthesis and anthocyanin synthesis,such as starch and sucrose metabolism（ko00500）,fructose and mannose metabolism（ko00051）,phenylpropanoid biosynthesis（ko00940）,flavonoid biosynthesis（ko00941）,arginine and proline metabolism（ko00330）and cysteine and methionine metabolism（ko00207）.The expression levels of key genes involved in the metabolic pathways of（IV,HK,SS and SPS）,phenylpropanoid（PAL,C4H,and 4CL）,flavonoid（CHS,CHI,F3’H,DFR and ANS）and（SAMDC,SPDS,SAMS,ADC and ODC）in the sheltered fruits were also up-regulated earlier than of those in the unsheltered fruits.The up-regulated of these genes were beneficial to the accumulation of sugar and anthocyanin content in fruit,and increase of fruit setting rate and fruit yield.According to the physiological indicators and transcriptional expression levels of the related genes,they are helpful to understand the effects of rain-shelter condition on Chinese cherry cultivation in rainy regions,furthermore,it also provide a new idea for planting China cherry under rain shelter condtion.