Sucrose Transporter AtSUC9 In Arabidopsis Thaliana Adapt To Abiotic Stress And Its Mechanism

Sucrose, as the product of photosynthesis, is the source of carbon and energy in plants. It plays an important role in regulating plant growth and stress tolerance. However, adversity (stress) environment inhibits photosynthesis in order to affect the sucrose supply, leading to reduce the plant stress tolerance. Therefore, the sucrose transport and distribution become key factors in plant stress resistance. Sucrose transporters play an important role in sucrose trans-port from source leaves to sink organs, and are also important factors in regulating plant growth and stress tolerance. At present, nine members (AtSUC1-9) in Arabidopsis SUT gene family have been defined, AtSUC9 is a super high-affinity sucrose transporter. However, the biological functions of AtSUC9 are not yet clear in vivo.In the research, we screened three T-DNA insert homozygous mutants Atsuc9-1, Atsuc9-4 and Atsuc9-5 in Arabidopsis thaliana. The three mutants and wild type (WT) as experimental materials. Firstly, under abiotic stress (salt, osmotic and cold stresses), we observed and measured the germination of AtSUC9 mutant seeds and seedling growth, the changes of AtSUC9 expression in WT, and the changes of sucrose distribution in AtSUC9 mutants. Moreover, under low sucrose concentration, we detected the changes of low sucrose level-responsive genes expression in AtSUC9 mutants, the changes of AtSUC9 mutants growth and sucrose content distribution, the changes of stress induced-,AtSUC9 mutants phenotype; Finally, under abiotic stress, we detected the content of abscisic acid (ABA) in AtSUC9 mutants; under exogenous ABA treatments, we detected the changes of ABA-inducible and stress-responsive genes expression. The goal of these research is to explore the mechanism of AtSUC9 in plant adaptation to abiotic stress. The main results are as follows:1. Under normal conditions, AtSUC9 mutants and WT seeds germination have a significant difference in the germination rate at the early stage; with the increase of treatment time, the germination rate of AtSUC9 mutants and WT seeds are basically the same. Under salt and osmotic and cold stresses, AtSUC9 mutants and WT have a more significantly difference; compared with WT, the germination rate of AtSUC9 mutants decreased significantly.2. Under normal conditions, AtSUC9 mutants and WT growth are not obviously different. Under salt, osmotic and cold stresses, AtSUC9 mutants and WT growth have a significantly difference; compared with WT, AtSUC9 mutants have shorter root, smaller leaf area, and growth retardation.3. The expression of AtSUC9 in the shoot and root in WT is up-regulated by salt, osmotic and cold stress treatments.4. Under normal conditions, the sucrose content of the shoot in AtSUC9 mutants and WT have little different, but the sucrose content of the root in AtSUC9 mutant is significantly lower than that in WT; under salt and osmotic and cold stresses, the sucrose content of the shoot in WT is significantly increased compared with normal condition; meanwhile, compared with WT, the sucrose content of AtSUC9 mutants are much higher in the shoot and lower in the root; with the increase of stress concentration, the difference of sucrose concentration in the shoot and root between AtSUC9 mutants and WT is more significant.5. The expression of AtSUC9 is induced by low levels of endogenous and exogenous sucrose, and deletion of AtSUC9 affects the expression of the low sucrose level-responsive genes.6. Under low concentrations of exogenous sucrose treatment, AtSUC9 mutants seed germination is delayed, seedling growth is inhibited, and sucrose distribution in the shoot and root of mutants is changed; AtSUC9 mutants hardly grow in abiotic stress treatments without exogenous sucrose.7. Under normal conditions, the ABA content of the shoot and root in AtSUC9 mutants is higher than that in WT. Compared with normal condition, salt, osmotic and low temperature treatments show the higher ABA content of the shoot and root in WT and the lower in AtSUC9 mutants.8. Under ABA treatments, the expression of ABA-inducible and stress-responsive genes (SnRK2.2/2.3/2.6, ABF2/3/4, ABIl/3/4, RD29A, KIN1 and KIN2) is inhibited in AtSUC9 mutants. AtSUC9 mutants are more sensitive under ABA treatments. Compared with WT, Atsuc9-1/Atabil-1 double mutants enhance plant abiotic stress tolerance.These results indicate that AtSUC9 is induced by low sucrose levels then mediates the balance of sucrose distribution and promotes ABA accumulation to enhance Arabidopsis thaliana abiotic stress resistance.