Dynamic Changes of Jasmonic Acid Biosynthesis in Rice Florets during Natural Anthesis

Abstract

Exogenously applied jasmonic acid (JA) or its methyl ester (MeJA) could significantly induce floret opening in gramineous plants such as rice, wheat, sorghum and rye. However, whether the endogenous JA is involved in the regulation of rice floret opening has remained unclear. To elucidate the role of endogenous JA in natural floret opening, we measured the JA levels in florets of Wuyunjing 7 (japonica cultivar) and Minghui 63 (indica cultivar) by HPLC-electrospray ionization tandem mass spectrometry system (HPLC-MS/MS) during natural anthesis, and analyzed the expression of key genes involved in JA biosynthesis in florets of Wuyunjing 7 by real-time reverse transcription-PCR (real-time RT-PCR). The results showed that the JA levels in rice florets were related with the process of anthesis. JA levels in rice florets kept relatively constant before anthesis in the morning, and reached a peak rapidly during anthesis, and then decreased after the floret closing. The peak levels of JA in opening florets were 4–5 times higher than those in florets 1 h before anthesis. Consistent with the changes of JA levels in florets during anthesis, the expression of OsDAD1-3, OsLOX-RCI1, OsAOS1, OsAOC, and OsOPR7 that encode isozymes catalyzing the key steps in JA biosynthetic pathway was up-regulated to some extent during floret opening, and was down-regulated after floret closing. Meanwhile, the levels of JA and transcripts of JA biosynthetic genes were higher in opening florets than in opened or closed florets at the same panicle. The increasing of JA levels and transcripts of JA biosynthetic genes in florets at the time of opening and their decreasing in florets after closing strongly indicated that endogenous JA is involved in the regulation of floret opening in rice.