Design and Functional Characterization of a Novel Abscisic Acid Analog

Abstract

The phytohormone abscisic acid (ABA) plays a crucial role in mediating plant growth and development by recruiting genetically redundant ABA receptors. To overcome its oxidation inactivation, we developed a novel ABA analog named 2′,3′-benzo-iso-ABA (iso-PhABA) and studied its function and structural characterization with A. thaliana ABA receptors. The (+)-iso-PhABA form showed much higher ABA-like activities than (+)-ABA including inhibitory effects on the seed germination of lettuce and A. thaliana, wheat embryo germination and rice seedling elongation. The PP2C (protein phosphatases 2C) activity assay showed that (+)-iso-PhABA acted as a potent and selective ABA receptor agonist, which is preferred to PYL10. In some cases, (−)-iso-PhABA showed moderate to high activity for the PYL protein inhibiting PP2C activity, suggesting different mechanisms of action of iso-PhABA and ABA. The complex crystal structure of iso-PhABA with PYL10 was determined and elucidated successfully, revealing that (+)-iso-PhABA was better coordinated in the same binding pocket compared to (+)-ABA. Moreover, the detailed interaction network of iso-PhABA/PYL10 was disclosed and involves hydrogen bonds and multiple hydrophobic interactions that provide a robust framework for the design of novel ABA receptor agonists/antagonists.

Synthesis and Biological Activity of 2′,3′-iso-Aryl-abscisic Acid Analogs

“…As shown in Scheme 1 , to obtain target compounds substituted- iso -PhABA ( 4b – 4d ) and heterocyclic analogs 2′,3′- iso -heterocylicABA ( iso -HetABA, 5a – 5d , 6 ), four different pathways (a–d in Scheme 1 ) for the preparation of dicarbonyl intermediates 9b – 9d , 13a – 13d , and 17 were established, respectively. Firstly, the preparation of intermediates 9b – 9d ( Scheme 1 a) were followed the similar pathway of the synthesis of 2′,3′- iso -PhABA 4 [ 25 , 27 ], comprising the vicinal methylation of the carbonyl of subtituted-1-tetralones (step i in Scheme 1 a) to obtain 8b – 8d and the oxidation of the benzyl carbon with Co(acac) 2 / t -BuOOH system [ 28 ] (step ii in Scheme 1 a). Then, for the preparations of pyridine analogs 13a – 13d , two different methods were applied for the intermediates 12a – 12d .…”

“…Furthermore, the alkynol intermediates 18 – 20 were also followed the two steps oxidation to give the acetylenic acid analogs 24b – 24d , 25a , 25b , 25d , and 26 (except 2′- n -Pr- iso -PyABA), since they are good materials for the screening of structural requirement of the trans-double bond of ABA analogs. Meanwhile, the acetylenic iso -PhABA 24a was synthesized following the similar pathway of 24b – 24d , with the known intermediate ( Z )-(1′-hydroxy-3′,3′-dimethyl-4′-oxo-tetrahydronaphthalene-one-yl)-3-methyl-pentyl-2-em-4-yn-1-ol [ 27 ].…”

“…6-Methoxy-2,2-dimethyl-3,4-dihydronaphthalen-1(2 H )-one ( 8b ) [ 25 , 27 ]: To a stirred solution of 6-methoxy-3,4-dihydronaphthalen-1(2 H )-one 7b (10.0 g, 56.8 mmol) dissolved in dry tetrahydrofuran (THF, 150 mL) in a 500 mL round bottomed flask was added NaH (11.4 g, 284 mmol, 60% in oil). After stirring the mixture for 1 h under ice-water bath, methyl iodide (32.3 g, 227 mmol) in dry THF (50 mL) was added slowly.…”

“…A successful case of 8′-hydroxylation resistant analog was 2′,3′-benzoabscisic acid 2 [ 24 , 25 ] ( Figure 1 ), which had excellent bioactivity and relatively efficient synthetic route. Inspired by this compound and iso -ABA 3 [ 26 ], in our previous works, we had developed 2′,3′- iso -Benzoabscisic acid ( iso -PhABA) 4a [ 27 ], which is an excellent and easier preparation ABA analog. The deeply investigations of bioactivity and agonist-receptor interactions for 4a suggested that it is a state-of-art ABA-like regulator and a selective ABA agonist, i.e., PYL10 has the highest inhibitory effect on the phosphatase activity of HAB1 in the presence of (+)- iso -PhABA.…”

The effect of a novel powerful ABA mimic on the improvement of color in grapes and its mechanism

“…Over the past decades, numerous institutes, including our team, have focused on the development of new stable ABA analogs with better in vivo antimetabolite and in vitro anti-photo-isomerization activities [24][25][26][27]. In a previous study, we developed 2′,3′-iso-benzoabscisic acid (iso-PhABA), an excellent and easily prepared ABA analog that can inhibit metabolism in vivo [28]. This study mainly focused on the role of iso-PhABA in the pigmentation and quality of the two grape varieties 'Jufeng' and 'Xiahei' to discover a novel and potential colorant for grapes.…”