Functional Study Of MdMRLK2 Under Stress Resistance In Malus

Receptor-Like Kinases(RLKs)are a class of single-transmembrane proteins containing a receptor domain that contain a serine/threonine kinase domain that recognizes extracellular signals during plant growth and play an important role in development and hormonal regulation.The function of the FER gene in Arabidopsis has been widely reported in recent years,but there are limited reports on such genes in apple.In this study,we systematically compared all FER genes in apple genome,and selected MdMRLK2 which showed the highest similarity with Arabidopsis FER as the research object.The MdMRLK2overexpression and RNAi transgenic plants were successfully obtained by the genetic transformation mediated by Agrobacterium tumefaciens.The function of MdMRLK2 in regulating drought,salt stress and Vasa canker disease resistance was identified by using the transgenic plants as materials.The main results obtained are as follows:1.Characterization of MdMRLK2.Gene expression analysis of MdMRLK2 revealed that MdMRLK2 was expressed in different tissues of apple plants and peaked in roots.Under drought stress,salt stress and Vasa mali infection stresses,the expression of MdMRLK2showed a decreasing trend with the increase of treatment time,indicating that MdMRLK2was involved in defense responses for both biotic and abiotic stresses.2.Functional Analysis of MdMRLK2 under Drought Stress.MdMRLK2 overexpression transgenic apple plants were treated by with holding water for 8 days.By detecting relative water content,relative conductivity,net photosynthetic rate,transpiration rate,chlorophyll content and stomatal opening degree,it is observed that the relative conductivity and stomatal opening of over-expressed plants were significantly higher in MdMRLK2overexpression transgenic apple plants than that of wild-type.The drought resistance of transgenic apple plants overexpressing MdMRLK2 was reduced.3.Functional Analysis of MdMRLK2 under Salt Stress.The MdMRLK2 overexpression transgenic apple seedlings were treated with 100 mM NaCl.The results showed that the chlorophyll content in transgenic plants was lower than that of the WT.Additionally,the net photosynthetic rate for 35S::MdMRLK2 was significantly lower than that of WT under 100mM NaCl condition.The relative conductivity was significantly higher than that of WT.The Na~+content in 35S::MdMRLK2 leaves was 1.7 times higher than that in WT.All the parameters indicated that the apple plants were more sensitive to salt stress when MdMRLK2being overexpressed.4.Regulation of MdMRLK2 in defense against Valsa canker disease.The35S::MdMRLK2 transgenic apple plants were inoculated with Valsa mali,and the size of the lesion after inoculation was observed.The results showed that MdMRLK2 overexpression made apple plants more sensitive to the Valsa canker pathogen.