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Phospholipase A <sub>2</sub> β mediates light-induced stomatal opening in <i>Arabidopsis</i>
Seo, Jiyoung,Lee, Hyoung Yool,Choi, Hyunju,Choi, Yunjung,Lee, Yuree,Kim, Yong-Woo,Ryu, Stephen Beungtae,Lee, Youngsook Oxford University Press 2008 Journal of experimental botany Vol.59 No.13
<P>Phospholipase A<SUB>2</SUB> (PLA<SUB>2</SUB>) catalyses the hydrolysis of phospholipids into lysophospholipids and free fatty acids. Physiological studies have indicated that PLA<SUB>2</SUB> is involved in stomatal movement. However, genetic evidence of a role of PLA<SUB>2</SUB> in guard cell signalling has not yet been reported. To identify <I>PLA</I><SUB>2</SUB> gene(s) that is (are) involved in light-induced stomatal opening, stomatal movement was examined in <I>Arabidopsis thaliana</I> plants in which the expression of <I>PLA</I><SUB>2</SUB> isoforms was reduced or knocked-out. Light-induced stomatal opening in <I>PLA</I><SUB>2</SUB><I>α</I> knockout plants did not differ from wild-type plants. Plants in which <I>PLA</I><SUB>2</SUB><I>β</I> was silenced by RNA interference exhibited delayed light-induced stomatal opening, and this phenotype was reversed by exogenous lysophospholipids, which are products of PLA<SUB>2</SUB>. Stomatal opening in transgenic plants that over-expressed PLA<SUB>2</SUB>β was faster than wild-type plants. The expression of <I>PLA</I><SUB>2</SUB><I>β</I> was localized to the endoplasmic reticulum of guard cells, and increased in response to light in the mature leaf. Aristolochic acid, which inhibits light-induced stomatal opening, inhibited the activity of purified PLA<SUB>2</SUB>β. Collectively, these results provide evidence that PLA<SUB>2</SUB>β is involved in light-induced stomatal opening in <I>Arabidopsis.</I></P>
Seo, Jiyoung,Kang, Su-Il,Kim, Mihyang,Han, Jaehong,Hur, Hor-Gil Springer-Verlag 2011 Applied microbiology and biotechnology Vol.91 No.2
<P>This review details recent progresses in the flavonoid biotransformation by bacterial non-heme dioxygenases, biphenyl dioxygenase (BDO), and naphthalene dioxygenase (NDO), which can initially activate biphenyl and naphthalene with insertion of dioxygen in stereospecfic and regiospecific manners. Flavone, isoflavone, flavanone, and isoflavanol were biotransformed by BDO from Pseudomonas pseudoalcaligenes KF707 and NDO from Pseudomonas sp. strain NCIB9816-4, respectively. In general, BDO showed wide range of substrate spectrum and produced the oxidized products, whereas NDO only metabolized flat two-dimensional substrates of flavone and isoflavone. Furthermore, biotransformation of B-ring skewed substrates, flavanone and isoflavanol, by BDO produced the epoxide products, instead of dihydrodiols. These results support the idea that substrate-driven reactivity alteration of the Fe-oxo active species may occur in the active site of non-heme dioxygenases. The study of flavonoid biotransformation by structurally-well defined BDO and NDO will provide the substrate structure and reactivity relationships and eventually establish the production of non-plant-originated flavonoids by means of microbial biotechnology.</P>
Seo, Jiyoung,Ryu, Ji-Young,Han, Jaehong,Ahn, Joong-Hoon,Sadowsky, Michael J,Hur, Hor-Gil,Chong, Youhoon Springer International 2013 Applied microbiology and biotechnology Vol.97 No.2
<P>Wild-type naphthalene dioxygenase (NDO) from Pseudomonas sp. strain NCIB 9816-4 transforms relatively planar flavone and isoflavone to cis-dihydrodiols. However, this enzyme cannot catalyze the transformation of flavanone and isoflavanone in which a phenyl group bonds to the stereogenic C2 or C3 of the C-ring. Protein modeling suggested that Phe224 in the substrate binding site of NDO may play a key role in substrate specificity toward flavanone and isoflavanone. Site-directed mutants of NDO with substitution of Phe224 with Tyr biotransformed only the (S)-stereoisomers of flavanone and isoflavanone, producing an 8-OH group on the A-ring. In contrast, the Phe224Cys and Phe224Gln substitutions, which used (2S)-flavanone as a substrate, and Phe224Lys, which transformed (2S)-flavanone and (3S)-isoflavanone, each showed lower activity than the Phe224Tyr substitution. The remainder of the tested mutants had no activity with flavanone and isoflavanone. Protein docking studies of flavanone and isoflavanone to the modeled mutant enzyme structures revealed that an expanded substrate binding site, due to mutation at 224, as well as appropriate hydrophobic interaction with the residue at 224, are critical for successful binding of the substrates. Results of this study also suggested that in addition to the previously known Phe352, the Phe224 site of NDO appears to be important site for expanding the substrate range of NDO and bringing regiospecific and stereospecific hydroxylation reactions to C8 of the flavanone and isoflavanone A-rings.</P>