Molecular Design, Synthesis And Bioactivity Of ABA Functional Analogue Based On Pyrabactin

Crop yield is largely restricted by environmental stresses, which could be possibly addressed by the treatment of phytohormones and their synthetic analogs. The phytohormone abscisic acid (ABA) plays critical roles on plant growth and helps to resist various environmental stresses. However, the application of ABA to enhance crop stress tolerance is largely restricted by its high cost and instability. Recent breakthroughs on ABA receptors identified a new chemical, named Pyrabactin, functions like ABA in the aspect of inhibiting seed germination in Arabidopsis. As Pyrabactin is more structurally stable than ABA and has a low production cost, we proposed that Pyrabactin can serve as a leading compound structure to design and screen new ABA analogs. To this end, nineteen compounds were designed and synthesized to assess their biological activities compared with ABA in inhibition of germination, stomatal closure and induced resistance to abiotic stresses using wheat. Our results lay a foundation to develop new chemicals that could enhance crop tolerance to environmental stresses. The key results are as followed:1. We synthesized Pyrabactin and conducted seed germination tests on Arabidopsis, wheat and mung bean. Based on the structure of Pyrabactin and coronatine, nineteen compounds (arylamino-cyclopropanecarboxylic acid) were then designed and synthesized by replacing2-Picolylamine with1-aminocyclopropanecarboxylic acid, changing sulfonyl to formoxyl and altering different substituted benzenes. Biological screening was performed to quantify their potential ABA-like activities, including inhibition of seed germination and response of stomata. The molecular interaction with Py12protein, one of ABA receptors, was also simulated on computer. Along with wheat seed germination test and stomatal response of broad bean leaf, four new chemicals, named B2, B5, B9, and B15, were found to have ABA-like function, especially for inhibition of wheat seed germination.2. The potential of B2, B5, B9, and B15on promoting wheat to resist salt stress was then assessed under hydroponic condition using wheat cultivar Jimai22. By referring to the phenotypic responses including biomass and root growth, salt stress at150mM and the rate of ABA and ABA analogs at0.01μM were chosen for more detailed research. The data showed that all compounds enhanced salt stress tolerance at seedling stage of wheat. At150mM NaCl, all compounds increased salt tolerance and showed comparable activity to ABA at0.01μM. Interestingly, B2showed higher activities than ABA in the aspect of root biomass of wheat seedling under salt-stressed condition. B2increased shoot and root biomass by159%and310%, respectively, when compared with untreated control at150mM NaC1. B2also promoted wheat growth under normal conditions:the fresh biomass of shoot and root was60%and45%higher than control, respectively.3. We further explored the physiological mechanism of B2-induced stress tolerance by monitoring the photosynthetic system, antioxidant defense system, endogenous hormone profile and the expression of stress-related genes. All these parameters measured responded to B2treatment. B2inhibited the transpiration rate by22%, increased the photosynthetic rate by18%at72hours after growing under salt-stressed condition. B2also reduced the level of·O2-, H2O2, malondialdehyde and electrolyte leakage by23%,16%,33%and37%, respectively. The activities of various antioxidant enzymes, and soluble sugar content were enhanced by B2treatment. B2also regulated the levels of various endogenous hormones, of which the level of zeatin was increased by205%. TaSOSl gene was up-regulated by B2treatment. B2up-regulated TaTIP2;2gene under normal condition, but down-regulated this gene under salt-stressed condition. We believe these physiological adjustments are responsible for B2-induced tolerance to salt stress.4. In conclusion, we showed a new way of designing ABA analogue by modifying the structure of Pyrabactin. It should be emphasized that B2showed higher biological activity than ABA in the aspect of inhibiting wheat seed germination and enhancing wheat tolerance to salt stress. Since these new compounds have much more stable structure and lower cost than ABA, their application in agriculture could be profound on many important crops on a global basis. Therefore, further studies are needed to completely screen this new family of chemicals.