The Effect Of Exogenous Methyl Jasmonate On The Flowering Time, Floral Organ Morphology, And Transcript Levels Of A Group Of Genes Implicated In The Development Of Oilseed Rape Flowers (Brassica Napus L.)

Oilseed rape (Brassica napus L.) is grown throughout the world as an important source of edible oil. The economic significance of the crop demands for intensive studies on the physiological processes, including the transition from vegetative to reproductive stage, indicated by timely flowering and well developed floral organs. A delayed flowering time, an insufficient flowering period or abnormal floral organs may result in a significant yield decline in oilseed rape. The appropriate development of a plant flower is resulted from a delicate balance between the internal and external environmental cues. Jasmonates (JAs) play important roles in the process of floral organ initiation and differentiation. In this study, we investigated the effect of exogenous methyl jasmonate (MeJA) on flowering time, floral organ morphology and expression pattern of a group of putative homeotic genes in winter oilseed rape (Brassica napus). We found that the application of exogenous MeJA gave rise to early flowering and various kinds of floral organ abnormalities. The reduction of time to flower varied between 1.9 to 3.5 days among 6 winter rapeseed cultivars. Furthermore, the application of high concentrations of MeJA (100μmol/L) also produced various kinds of abnormal flowers. The dosage effect was investigated by counting the number of the open flowers induced and analyzing the RNA transcriptional levels of the JA-inducible genes. Various kinds of floral organ abnormality induced by the exogenous MeJA were characterized by the description of morphological floral structures, and the analysis of expression pattern of the group of putative homeotic genes specifying floral organs and other transcriptional factors that are important for the biosynthesis of JA and transduction of JA signal. Our results demonstrated that the combined actions of the floral identity genes, specifically BnAP1, BnAP2, BnAP3, BnAG1, and BnPI3, as reflected by their respective relative transcript levels, were responsible for causing the different kinds of flower abnormalities previously undescribed in oilseed rape.