Jasmonates are important phytohormones regulating reproductive development. We used two recessive rice Tos17 alleles of OsJAR1, osjar1-2 and osjar1-3, to study the biological function of jasmonates in rice anthesis. The florets of both osjar1 alleles stayed open during anthesis because the lodicules, which control flower opening in rice, were not withering on time. Furthermore, dehiscence of the anthers filled with viable pollen, was impaired, resulting in lower fertility. In situ hybridization and promoter GUS transgenic analysis confirmed OsJAR1 expression in these floral tissues. Flower opening induced by exogenous applied methyl jasmonate was impaired in osjar1 plants and was restored in a complementation experiment with transgenics expressing a wild type copy of OsJAR1 controlled by a rice actin promoter. Biochemical analysis showed that OsJAR1 encoded an enzyme conjugating jasmonic acid (JA) to at least Ile, Leu, Met, Phe, Trp and Val and both osjar1 alleles had substantial reduction in content of JA-Ile, JA-Leu and JA-Val in florets. We conclude that OsJAR1 is a JA-amino acid synthetase that is required for optimal flower opening and closing and anther dehiscence in rice.
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Acknowledgments The Tos17 lines used in this work were developed by Drs. Akio Miyao and Hirohiko Hirochika (Miyao et al. 2003) and were provided by the Rice Genome Resource Center (Tsukuba, Japan). We are grateful to Gerda Lamers for her technical support in microscopy. We thank Ward de Winter for tissue culture media and Elly Schrijnemakers for plant caretaking. This research was supported by the Programme for Strategic Scientific Alliances (04-PSA-BD-04) between China and the Netherlands of the Royal Netherlands Academy of Arts and Sciences (KNAW) for MW, PBFO, YX, ZZ and the KNAW China Exchange Programme (KNAW-CEP 04CDP022, 06CDO033, 07CDP005, 08CDP042) for YX and YC. We acknowledge financial support from the Netherlands Organization for Scientific Research (NWO; VICI-grant) to HJB, TC and PPJM.