| During the entire growth cycle of plants,it is inevitable to encounter various environmental stresses,among which salt stress is the more common one.Excessive Na+will further cause damages such as osmotic stress,ion imbalance and oxidative stress,and plants also respond and adapt to salt stress through a series of signaling ways.Plant meristem is the basis of plant growth and development.Among them,the stem apex meristem(SAM)differentiates the aerial part of the plant,including flowers,stems,leaves,etc..The vascular cambium(VCAM)determines the secondary growth of the plant,so that the stem grows laterally and becomes thicker.The root apex meristem(RAM)differentiates the underground root system of the plant.WUSCHEL(WUS),WOX4 and WOX5,members of the Arabidopsis WOX protein family,are expressed in shoot apical meristem,vascular cambium and root apical meristem,respectively,and maintain the functions of the corresponding stem cells with the CLE family members(CLV3,CLE41/44 and CLE40)together.However,it is remains to be elucidated how plant stem cells response and adapt to environmental salt stress.Leucine aminopeptidases(LAPs)are highly conserved dizinc metal lopeptidases.Studies have shown that in addition to peptidase-related functions,LAPs can also act as molecular chaperones and play a role in plant resistance to external stress.In this work,the roles of LAP 1 and LAP2 in stem cell function had been investigated in Arabidopsis thaliana in response to salt stress.Our results showed that LAP1 protein was expressed in all organ during the entire development process of Arabidopsis thaliana.Most of the LAP1 protein was located in the cytoplasm with a small part located in the nucleus,and the LAP2 protein was located in the chloroplast.Salt stress promoted the expression of LAP1 and LAP2 proteins and increased the amounts of proteins in the nucleus.Bimolecular fluorescence complementation(BiFC),Pull-down,electrophoretic mobility shift assay(EMSA)and luciferase assay(LUC)had proved that the LAP 1 and LAP2 proteins interacted with WUS,WOX4 and WOX5 proteins as a complex,which further bound to the WUS/WOX4/WOX5 promoters,respectively,to promote their expression.Under salt stress,LAP1 and LAP2 proteins could maintain the function of plant stem cells.The loss of LAP1 or LAP2 function alone did not affect the tolerance of Arabidopsis to salt stress.In the presence of loss-of-function of LAP1 and LAP2,Arabidopsis thaliana was more sensitive to salt stress,resulting in the severe inhibition of germination,leaf differentiation and root elongation.This work had discovered the roles of leucine aminopeptidases in plant stem cell function under salt stress,which provided a pathway to breed new crop species with high salt resistance in the future. |
