Publications (22) View all
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Article: Auxins increase expression of the brassinosteroid receptor and brassinosteroid-responsive genes in Arabidopsis.
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ABSTRACT: Auxins and brassinosteroids are essential phytohormones that synergistically regulate physiological and developmental processes in plants. Previously, we demonstrated that auxins stimulate brassinosteroid perception by regulating the level of brassinosteroid receptor in rice. Here we showed that auxin treatment increased expression of the Arabidopsis brassinosteroid receptor gene BRI1. The promoter of BRI1 has an auxin-response element that is targeted by auxin-response factor transcription factors. Auxin pretreatment increased the sensitivity to brassinosteroids of brassinosteroid-responsive genes. Although multilevel interactions between auxins and brassinosteroids have previously been reported, our findings suggest a possibility that auxins control the degree of brassinosteroid perception by regulating the expression of gene for brassinosteroid receptor, and this phenomenon is conserved between monocots (rice) and dicots (Arabidopsis).Plant signaling & behavior 01/2013; 8(4). -
Article: Auxin signal transcription factor regulates expression of brassinosteroid receptor gene in rice.
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ABSTRACT: The phytohormones auxin and brassinosteroid are both essential regulators of physiological and developmental processes, and it has been suggested that they act interdependently and synergistically. In rice (Oryza sativa), auxin co-application improves the brassinosteroid response in the rice lamina inclination bioassay. Here, we showed that auxin stimulates brassinosteroid perception by regulating the amount of brassinosteroid receptors. Auxin treatment increased expression of the rice brassinosteroid receptor gene OsBRI1. The promoter of OsBRI1 has an auxin response element (AuxRE) that is targeted by auxin response factor (ARF) transcription factors. An AuxRE mutation abolished the induction of OsBRI1 expression by auxins, and OsBRI1 expression was downregulated in an arf mutant. The AuxRE motif in the OsBRI1 promoter, and thus the transient upregulation of OsBRI1 expression caused by IAA treatment, is essential for an IAA-induced increase in sensitivity to brassinosteroids. These findings demonstrate that some ARFs control the degree of brassinosteroid perception required for normal growth and development in rice. Although multilevel interactions between auxins and brassinosteroids have previously been reported, our findings suggest a mechanism by which auxin controls cellular sensitivity to brassinosteroids, and further support the notion that interactions between auxin and brassinosteroid are extensive and complex. © 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.The Plant Journal 11/2012; · 6.16 Impact Factor -
Article: Rice CYP90D2 and CYP90D3 catalyze C-23 hydroxylation of brassinosteroids in vitro.
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ABSTRACT: Brassinosteroids are biosynthesized from campesterol via several cytochrome P450 (P450)-catalyzed oxidative reactions. We report the biochemical characterization of two brassinosteroid-biosynthetic P450s from rice: CYP90D2 and CYP90D3. A rice dwarf mutant, ebisu dwarf (d2), which contains a defective copy of CYP90D2, is known to be a brassinosteroid-deficient mutant, and CYP90D2 has been considered to act as a C-3 dehydrogenase. However, in vitro biochemical assays using baculovirus/insect cell-produced proteins revealed that both CYP90D2 and CYP90D3 catalyze C-23 hydroxylation of various 22-hydroxylated brassinosteroids, but with markedly different catalytic efficiencies. Both enzymes preferentially convert (22S,24R)-22-hydroxyergost-4-en-3-one, (22S,24R)-22-hydroxy-5α-ergostan-3-one, and 3-epi-6-deoxocathasterone to the corresponding 23-hydroxylated products, but are less active in the conversion of (22S)-22-hydroxycampesterol and 6-deoxocathasterone, in vitro. Consistently, the levels of 23-hydroxylated products of these intermediates, namely, 6-deoxoteasterone, 3-dehydro-6-deoxoteasterone, and 6-deoxotyphasterol were decreased in d2 mutants. These results indicate that CYP90D2 and CYP90D3 can act as brassinosteroid C-23 hydroxylases in rice.Plant Physiology and Biochemistry 07/2012; 58:220-6. · 2.84 Impact Factor -
Article: Rice CYP734As function as multisubstrate and multifunctional enzymes in brassinosteroid catabolism.
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ABSTRACT: Catabolism of brassinosteroids regulates the endogenous level of bioactive brassinosteroids. In Arabidopsis thaliana, bioactive brassinosteroids such as castasterone (CS) and brassinolide (BL) are inactivated mainly by two cytochrome P450 monooxygenases, CYP734A1/BAS1 and CYP72C1/SOB7/CHI2/SHK1; CYP734A1/BAS1 inactivates CS and BL by means of C-26 hydroxylation. Here, we characterized CYP734A orthologs from Oryza sativa (rice). Overexpression of rice CYP734As in transgenic rice gave typical brassinosteroid-deficient phenotypes. These transformants were deficient in both the bioactive CS and its precursors downstream of the C-22 hydroxylation step. Consistent with this result, recombinant rice CYP734As utilized a range of C-22 hydroxylated brassinosteroid intermediates as substrates. In addition, rice CYP734As can catalyze hydroxylation and the second and third oxidations to produce aldehyde and carboxylate groups at C-26 in vitro. These results indicate that rice CYP734As are multifunctional, multisubstrate enzymes that control the endogenous bioactive brassinosteroid content both by direct inactivation of CS and by the suppression of CS biosynthesis by decreasing the levels of brassinosteroid precursors.The Plant Journal 03/2011; 67(1):1-12. · 6.16 Impact Factor -
Article: Identifying and exploiting grain yield genes in rice.
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ABSTRACT: Improved grain yield has been a major focus of crop breeding programs around the world. With the accomplishments of the Rice Genome Project, genes regulating several agronomically important traits related to grain yield, such as tiller number, grain number, grain size, and plant height, have recently been identified. Although these findings have not been enough to fully characterize the mechanisms that regulate each trait, these genes and knowledge of the molecular mechanisms involved provide a set of tools that can be combined to achieve tailor-made breeding suitable for various programs aimed at higher grain yield.Current Opinion in Plant Biology 05/2008; 11(2):209-14. · 9.27 Impact Factor
