| Drought stress is one of the abiotic stresses that often occur in Northwest China,affecting plant growth and development and even causing death.Desert plants enhance their drought resistance through different drought response modes.Among them,the formation of more developed leaf veins has obvious phenotypes in response to drought stress,but less attention has been paid.The more developed the leaf veins,the stronger the drought resistance.The leaf vein vascular system provides water and inorganic salts for the leaves,and outputs photosynthetic products.The water transport mainly depends on the xylem.The HD-ZIP III family of transcription factors,which are determinants of xylem development on the adaxial surface of leaves,play a wide-ranging role in regulating plants from birth to death.REVOLUTA is one of the family members.Its mutational characteristics describe the consequences of the loss of HD-ZIP III function for the first time,including the decrease in the number of vessels and the area of xylem.On the contrary,rev-10 d shows a significant increase in the number of vessels in the xylem and forms vascular bundle phenotype with xylem surrounding phloem.Moreover,HD-ZIP III transcription factor determines the characteristics of xylem cells in a dose-dependent manner.High doses lead to metaxylem,and low doses promote the formation of protoxylem.The current research on the drought resistance of Caragana korshinskii mainly focuses on physiological characteristics and other aspects.The preliminary laboratory research found that as the drought intensified,the xylem of the drought-resistant pioneer plant Caragana korshinskii became more developed.In this study,CkREV was used as a starting point to analyze the molecular mechanism of CkREV regulating leaf vein secondary development and enhancing plant drought resistance in Caragana korshinskii drought response.The main research results of this experiment are as follows:1.Through in situ hybridization and immunohistochemistry experiments,the tissue level location of Caragana korshinskii CkREV at different developmental stages was analyzed.The results showed that Caragana korshinskii CkREV was specifically expressed in the xylem of Caragana korshinskii vascular bundle at different developmental stages,regardless of RNA level or protein level,especially vessel cells and adjacent cells.It participates in the differentiation of vessel cells and its programmed cell death process or regulates the formation of raw material molecules for vessel synthesis,thereby regulating the development of xylem cells and providing a spatiotemporal basis for determining the fate of paraxial cells.2.The protein level interaction between CkREV and Ck AS1 was verified by bimolecular fluorescence complementation(BIFC)and yeast two hybrid(Y2H).Under drought-response conditions,CkREV recruited Ck AS1 to directly down-regulate the expression of Ck YUC5 and reduce the content of auxin to slow down its own growth rate and reduce the plant’s water demand.On the other hand,CkREV can directly bind to the promoter region of Ck LAX3 in the xylem.The region up-regulates the expression of Ck LAX3 and guides the directional transport of synthesized auxin to the xylem.At the same time,it is induced by auxin to form a positive feedback loop that promotes the function of CkREV and affects the development of the vessel.3.In response to drought,Caragana korshinskii CkREV directly positively regulates the expression of Ck VNDs and lignin synthesis rate-limiting enzyme Ck PAL4 related to xylem vessel differentiation,combined with the downstream transcriptional regulatory cascade network of Ck VNDs,and jointly promotes cellulose,lignin and xylan are deposited in the differentiated xylem vessels,which directly regulate the development of vessels and enhance the drought resistance of plants.4.Under the drought response of Caragana korshinskii CkREV,it promotes plants to form more developed xylem vessels through various means,which significantly improves the drought resistance of plants.We performed simulated drought and natural drought treatments on transgenic Arabidopsis.With the intensification of drought,the CkREV-OE strain has significantly better growth status,lower ROS levels and stomata opening than no-load and wild-type Arabidopsis.The determination of physiological indicators further supports the above result.In summary,under the drought response of Caragana korshinskii CkREV,on the one hand,it promotes the formation of auxin gradients and provides a large environment for the formation of more prosperous veins in the leaves of Caragana korshinskii.Feedback loop.In addition,CkREV can bind to the promoter regions of Ck VNDs and Ck PAL4,directly and positively regulate the expression of Ck VNDs and lignin synthesis rate-limiting enzyme Ck PAL4 related to xylem duct differentiation,and through the transcriptional regulation cascade network downstream of Ck VNDs,It promotes the deposition of cellulose and xylan in the differentiated xylem vessels,and promotes the formation of more frequent veins in the leaves of Caragana korshinskii,which significantly improves the drought resistance of the plant. |
