Zealactones. Novel natural strigolactones from maize.

In the root exudate and root extracts of maize hybrid cv NK Falkone seven putative strigolactones were detected using UPLC-TQ-MS-MS. All seven compounds displayed MS-MS-fragmentation common for strigolactones and particularly the presence of a fragment of m/z 97 Da, which may indicate the presence of the so-called D-ring, suggests they are strigolactones. The levels of all these putative strigolactones increased upon phosphate starvation and decreased upon fluridone (carotenoid biosynthesis inhibitor) treatment, both of which are a common response for strigolactones. All seven compounds were subsequently isolated with prep-HPLC-MS. They all exhibited Striga hermonthica seed germination inducing activity just as the synthetic strigolactone analog GR24. The structure of two of the seven compounds was elucidated by NMR spectroscopy as: methyl (2E,3E)-4-(3,3-dimethyl-5-oxo-2-(prop-1-en-2-yl)tetrahydrofuran-2-yl)-2-(((4-methyl-5-oxo-2,5-dihydrofuran-2-yl)oxy)methylene)but-3-enoate (two diastereomers 1a and 1b). Strigolactones (1a/b) are closely related to the methyl ester of carlactonoic acid (MeCLA) and heliolactone. However, they contain a unique 4,4-dimethyltetrahydrofuran-2-one motif as the "A-ring" instead of the classical (di)methylcyclohexene. Because these compounds were isolated from maize (Zea mays) we called them "zealactone 1a and 1b". The implications of this discovery for our view on strigolactones and their biosynthesis are discussed.

Cloning and functional analyses of a gene from sugar beet up-regulated upon cyst nematode infection.

The cDNA-AFLP technique was used to isolate sugar beet genes up-regulated upon infection with the beet cyst nematode Heterodera schachtii. Hairy root cultures were obtained from resistant plants carrying a Beta procumbens translocation as well as from a non-resistant control. mRNA was isolated from hairy root clones and sugar beet plants infected or not with the beet cyst nematode and 8000 transcript-derived fragments (TDFs) were analysed. One TDF was found to be differentially expressed in both materials and was further investigated. Real-time PCR confirmed that this TDF is specifically up-regulated in resistant sugar beet upon nematode infection and its full-length cDNA was isolated. Sequence analysis suggests that the gene encodes a 317 amino acid polypeptide of unknown function. No homology to any sequence present in the public databases could be detected. To further elucidate its function in resistance to the beet cyst nematode, the cDNA was transformed into hairy roots of susceptible sugar beet under the control of the 35S promoter and hairy root clones were inoculated with nematodes. The number of developing females was significantly reduced in 12 out of 15 clones resulting from independent transgenic events suggesting that the gene can be used for inducing cyst nematode resistance in plants.