Studies On Screening And RNA-seq Of Drought Tolerant Hemerocallis

There are numerous arid and semi-arid areas in China,therefore,selection and cultivation of drought resistant garden and horticultural plant cultivars is the main research target of plant breeding cultivars of daylily.The preliminary screening based on leaf surface temperature measurement was performed to establish a simple,rapid and large-scale screening method for drought resistant.The drought resistance indexes,such as stomatal conductance,stomatal density,water loss rate and relative water content of leaves and the appearance of aerial part of selected daylily cultivars after drought stress treatment were measured to grade the drought resistance.The correlation analysis showed that there was a positive correlation between leaf temperature and drought resistance of daylily cultivars.The selected drought resistant and drought sensitive daylily cultivars were chosen for performing transcriptome sequencing.The difference genes were analyzed by several bioinformatic methods.This study will provide a rapid method for the selection of drought tolerant daylily cultivars,and rich gene information of daylily by transcriptome sequencing.The main research results are as follows:1.Due to the correlation between water loss and the leaf temperature of plants,a rapid and large-scale screening method for drought tolerant daylily cultivars was established.The leaf temperature of all daylily cultivars cultured in glass greenhouse was measured by precise infrared thermometer.Leaf temperature of 149 daylily cultivars was measured,and 8 daylily cultivars with the highest and lowest leaf temperature were selected for further analysis.The photosynthetic parameters,the water loss rate,relative water content and stomatal density of leaves of selected daylily cultivars were measured.The results here showed that ‘Mengzihua'was drought resistant.2.The experiment was carried out by using the method of potted water control to simulate the drought stress.According to the damage degree and morphological change of the experimental materials under the drought stress,the drought resistance evaluation criterion was established,and the drought resistance grade was divided.Combined this with the preliminary screening of leaf temperature,a set of evaluation system of drought resistance daylily cultivars was established.At the same time,the acquired score,photosynthetic characteristics and drought resistance indexes were used to test the correlation between the drought resistance and leaf temperature of daylily cultivars,to verify the feasibility of selecting the daylily varieties based on the leaf temperature,and to form a relatively rapid and accurate comprehensive evaluation system for the selection of drought resistance daylily cultivars.3.In order to further study the molecular mechanism of daylily response to drought stress,high-throughput sequencing technology was used to sequence the genes of diploid drought resistant variety ‘Mengzihua'and drought sensitive daylily cultivar ‘shy tiger'.In this experiment,the RNA-seq data here was compared with the database of plant transcription factors.Based on the analysis of KEGG,the key genes responsible for photosynthesis pathway were down regulated,which indicated that drought stress inhibited the photosynthesis of daylily.Among the genes related to osmoregulation,galactose metabolism,starch and sucrose metabolism are more active,indicating that these organic small molecules are helpful to improve the stress resistance of plant cells.The up-regulation of antioxidant genes indicates that drought stress can lead to the increase of active oxygen species,and the plant is under oxidative stress.It can inhibit the repair of cell membrane and DNA damage.