The Molecular Mechanism Of Salt Response In Chrysanthemum Lavandulifolium(Fisch.ex Trautv.) Makino

Salinity is one of the major abiotic stresses that adversely affect crop productivity and quality. It is estimated that more than 50%of the arable land would be salinized by the year 2050, unless some type of corrections aremade. Meanwhile, human population is on the rise and it is expected to reach 9.1 billion by 2050. With the available natural resources, it is becoming more challenging to meet the demands of the growing population, in particular when additional lands are becoming unusable for agriculture due to various environmental factors and urban expansion. Meanwhile, salinity adversely affect the development of the flower industry and the landscape planning, thus the cultivate of salt-tolerance ornamental plants is vital for urban landscaping. Chrysanthemum is traditional famous flower of China, also the important ornamental flowers and commodity flowers. Because of its complex genetic background, the progress of the salt-responsive molecular mechanism of chrysanthemum has been slowed.The objective of this study is to use the Chrysanthemum lavandulifolium (Fisch. ex Trautv.) Makino which is closely related to cultivated chrysanthemums as a model plant, to preliminary analysis its salt-responsive molecular mechanism and screening the salt-responsive candidate genes.Thus, we can understand the molecular mechanism of chrysanthemum indirectly.The main results were summarized as follows.1 The determination of physiological indexes of C. lavandulifolium under 100 mM, 200 mM and 300 mM NaCl treatments showed that 300 mM NaCl treatment during 3-6 d caused an irreversible injury to C. lavandulifolium seedlings; however, under 100 mM NaCl treatment during 12 d and 200 mM treatment during 6 d, five physiological parameters persistently increased, which indicates that C. lavandulifolium belongs to halophyte plants, and suggests that C. lavandulifolium had unique mechanisms to cope with salt stress.2 By using high-throughout transcriptome sequencing of C. lavandulifolium, RNA-Seq and tranditional omics-oriented analysis (cDNA-AFLP), we got the salt-responsive and salt-tolerance gene groups. We found that under short-term salt stress, MAPK. pathway genes, PP2C gene family, ABA pathway, NAC, WRKY and AP2/EREBP were the most up-regulated genes, while genes related mechanism and proteins were down-regulated, while the main responsive genes under long-term salt stress (48 h) in C. lavandulifolium were genes encoded ROS-removal and ion homeostasis3 Expression patterns and bioinformation analysis of two genes related to ion homeostasis, CISOS1 and ClAKT, indicated that, ClSOS1 mainly responded to salt in roots of C.lavandulifolium, while ClAKT encoded a potassium channel with new function. Over-expression the ClAKT gene in Arabidopsis thaliana could enhanced the tolerance for salt and drought, and the transgenic plants could highefficiency uptake potassium and efflux sodium.4 We first reported that the Nudix hydrolases famliy was functioned in abiotic stresses-responsive progress and signal transduction. CINUDX1, which could responsed to multi-stresses and hormonal tratments, may regulate the salt-responsive pathways by interacting with ABA and SA signal receptors in C. lavandulifolium.5 Our study of NAC gene family was the first report to study the function of this gene family in higher plants except model plants,10 CINAC genes could respond to at least 5 kinds of abiotic stresses belong to 7 different subfamilies were obtained, except for ATAF subfamily, other subfamilies were first reoprted to involved in abiotic stresses tolerance by us. Furthermore, ClATAF could regulated several node genes in A. thaliana, indicate its important roles during the stresses-responsive progress in C. lavandulifolium.In summary, our research showed that C. lavandulifolium belongs to halophyte plants, it respnsed to salt stress mainly by the genes encoding signal transduction and ion homeostasis. Based on the above conclusion, we have proposed the model of the molecular mechanism of salt response in C. lavandulifolium. The reports of new salt-responsive pathways and genes in this specie provided knowledge of molecular mechanism of salt-tolerance in higher plants, and provided genes resources for the gene engineering of chrysanthemum, which has important theoretical and practical significance.