Strigolactones (SLs) stimulate seed germination of root parasitic plants and induce hyphal branching of arbuscular mycorrhizal fungi in the rhizosphere. In addition, they have been classified as a new group of plant hormones essential for shoot branching inhibition. It has been demonstrated thus far that SLs are derived from carotenoid via a biosynthetic precursor carlactone (CL), which is produced by sequential reactions of DWARF27 (D27) enzyme and two carotenoid cleavage dioxygenases CCD7 and CCD8. We previously found an extreme accumulation of CL in the more axillary growth1 (max1) mutant of Arabidopsis, which exhibits increased lateral inflorescences due to SL deficiency, indicating that CL is a probable substrate for MAX1 (CYP711A1), a cytochrome P450 monooxygenase. To elucidate the enzymatic function of MAX1 in SL biosynthesis, we incubated CL with a recombinant MAX1 protein expressed in yeast microsomes. MAX1 catalyzed consecutive oxidations at C-19 of CL to convert the C-19 methyl group into carboxylic acid, 9-desmethyl-9-carboxy-CL [designated as carlactonoic acid (CLA)]. We also identified endogenous CLA and its methyl ester [methyl carlactonoate (MeCLA)] in Arabidopsis plants using LC-MS/MS. Although an exogenous application of either CLA or MeCLA suppressed the growth of lateral inflorescences of the max1 mutant, MeCLA, but not CLA, interacted with Arabidopsis thaliana DWARF14 (AtD14) protein, a putative SL receptor, as shown by differential scanning fluorimetry and hydrolysis activity tests. These results indicate that not only known SLs but also MeCLA are biologically active in inhibiting shoot branching in Arabidopsis.strigolactone | biosynthesis | cytochrome P450 | Arabidopsis | rice S trigolactones (SLs) are allelochemicals, exuded from plant roots, that stimulate seed germination of root parasitic plants, Striga spp., Orobanche spp., and Phelipanche spp. (1). The hyphal branching of the biotrophic arbuscular mycorrhizal (AM) fungi is also induced by SLs in the vicinity of host roots to ensure symbiosis with host plants (2). SLs are not only host recognition signals in the rhizosphere but also play important roles in the SLproducing plants themselves. Since the mid-1990s, the existence of novel hormone-like signals involved in shoot branching inhibition of plants had been proposed following the isolation and analysis of mutants with increased shoot branching, ramosus (rms) of pea (Pisum sativum), decreased apical dominance (dad) of petunia (Petunia hybrida), more axillary growth (max) of Arabidopsis (Arabidopsis thaliana), and dwarf (d) and high tillering dwarf (htd) of rice (Oryza sativa) (3-6). Recently, these mutants have been identified as SL-deficient or -insensitive mutants, providing decisive evidence that SLs function as shoot branchinhibiting hormones (7,8). In addition, further characterization of these mutants has shown that SLs affect root growth and development, leaf shape and senescence, internode elongation, secondary growth, and drought and salinity stress responses (9-11).Despit...

Plants exude strigolactones (SLs) to attract symbiotic arbuscular mycorrhizal fungi in the rhizosphere. Previous studies have demonstrated that phosphorus (P) deficiency, but not nitrogen (N) deficiency, significantly promotes SL exudation in red clover, while in sorghum not only P deficiency but also N deficiency enhances SL exudation. There are differences between plant species in SL exudation under P-and N-deficient conditions, which may possibly be related to differences between legumes and non-legumes. To investigate this possibility in detail, the effects of N and P deficiencies on SL exudation were examined in Fabaceae (alfalfa and Chinese milk vetch), Asteraceae (marigold and lettuce), Solanaceae (tomato), and Poaceae (wheat) plants. In alfalfa as expected, and unexpectedly in tomato, only P deficiency promoted SL exudation. In contrast, in Chinese milk vetch, a leguminous plant, and in the other non-leguminous plants examined, N deficiency as well as P deficiency enhanced SL exudation. Distinct reductions in shoot P levels were observed in plants grown under N deficiency, except for tomato, in which shoot P level was increased by N starvation, suggesting that the P status of the shoot regulates SL exudation. There seems to be a correlation between shoot P levels and SL exudation across the species/families investigated.

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The number of porcine epidemic diarrhea (PED) cases has increased over the past 20 years in Korea, with a major outbreak in 2013. A total of 27 Korean strains from 1998 to 2013 were analyzed (excluding the noncoding regions) and divided into two groups for comparison of the spike (S), ORF3, envelope (E), membrane (M), and nucleocapsid (N) genes with those of reference strains, vaccine strains, and previously identified strains based on phylogenetic analysis. Analysis of the selection patterns of PEDV isolated in Korea indicated positive selection of nine nonsynonymous sites in the S and N proteins and negative selection at 97 sites for all of the proteins. Interestingly, eight nonsynonymous mutations in S showed no significant pattern change over the 15-year period, and one of eight mutation sites was found only in IC05TK, GN05DJ, and KNU0802 in the epidemic years 2005 and 2008. These eight mutations were also present during the epidemic years in China. Furthermore, of the signs of positive selection in the S protein, the conservative substitutions were more frequent than radical substitutions in PEDVs, suggesting that the evolution of Korean strains has been slow. Serological cross-reactivity was detected between three field PEDVs and two vaccine strains, with different serum neutralization titers. In conclusion, although Korean PEDVs have been evolving slowly, their diverse antigenicity and genetics imply that multilateral efforts to prevent future PED outbreaks are required.

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