Functional Study Of MdPYL9 Gene Under Drought Stress In Malus

Under drought stress,plants accumulate a large amount of reactive oxygen species,which can lead to oxidative stress damage,affecting their normal growth,and even leading to plant death in severe cases.As the main apple producing area,Northwest of China is a typical arid area.The insufficient water supply seriously affects the yield and quality of apples.Therefore,it is of great significance to study the key genes and mechanisms of drought resistance in apple.As a plant stress hormone,ABA plays an important role in coping with drought stress.Previous studies of our group found that as a member of the ABA receptor family,the gene expression level of MdPYL9 that was significantly up-regulated under long-term drought stress.It was speculated that MdPYL9 may regulate the drought resistance of apple plants by affecting ABA signal.In order to deeply identify the function of MdPYL9,we carry out short-term and long-term drought treatments on MdPYL9-overexpressing transgenic apple plants.We compare various drought related indexes of transgenic and wild-type apple plants,such as net photosynthesis rate,chlorophyll content,conductivity,MDA content,antioxidant enzyme activity and relative water content of leaves.The results show that the overexpression of MdPYL9 gene could significantly improve the drought resistance of apple plants under drought stress.The main results are as follows:1.Under short-term drought stress,the stomatal conductance and chlorophyll content of MdPYL9-overexpressing apple plants are higher than those of wild-type plants,and the transgenic plants could maintain higher photosynthesis ability.In addition,the activity of antioxidant enzymes in transgenic plants is also higher than that in wild-type plants,and the ability of scavenging reactive oxygen species is stronger than that in wild-type plants.Accordingly,the contents of H₂O₂ and O₂^-in transgenic plants are lower than those in wild-type plants,and the results of reactive oxygen histochemical staining are also consistent with that in transgenic plants.MDA content and conductivity of transgenic plants are also lower than those of wild-type plants,indicating that the cell membrane system of transgenic plants suffering less damage.The relative water content of leaves in transgenic plants is higher than that in wild-type plants,which indicates that the water retention capacity of transgenic plants under drought stress is better than that of wild-type plants.These results indicate that overexpression of MdPYL9 could enhance the ability of plants to cope with short-term drought stress and enhance their drought resistance.In addition,we detect the expression of ABA signaling related genes on 6 days of drought treatment.The results show that the expression levels of ABI2 and HAB1 in transgenic plants are significantly lower than those in wild-type plants,suggesting that MdPYL9 is involved in the ABA signaling pathway in response to drought stress.2.Under long-term drought treatment,MdPYL9-overexpressing transgenic apple lines maintain better growth status.In addition,the photosynthetic value,chlorophyll content and relative water content of leaves in transgenic plants are also higher than those in wild-type plants,while MDA content is lower than that in wild-type plants.The results of NBT histochemical staining show that the content of O₂^-in transgenic plants is lower than that in wild-type plants.During drought treatment,the content of H₂O₂ in transgenic plants is lower than that in wild-type plants,while the activity of antioxidant enzymes is higher than that in wild-type plants.The above results show that MdPYL9 transgenic plants have better ability of scavenging reactive oxygen species than wild-type plants.They could accumulate more biomass under drought stress and have stronger drought resistance.During the long-term drought treatment,WUEi of transgenic lines is significantly higher than that of wild-type plants.After long-term drought treatment,the stomata length and width of transgenic plants in the treatment group are higher than those of wild-type plants,and stomatal density is slightly higher than that of wild-type plants.The above results indicate that MdPYL9transgenic plants could regulate stomatal size and density,thereby improving WUEi of plants under drought stress,enhancing the ability of plants to cope with long-term drought stress.The results of gene expression show that relative expression levels of SnRK2.4 and SnRK2.6 are significantly up-regulated in transgenic lines,indicating that MdPYL9 regulates the expression of downstream genes by interacting with ABA,thus improving drought resistance of plants.