Background: Capsaicinoid are a group of compounds and widely used in the food, medical, and pharmaceutical industries. Capsaicinoid are unique synthesized and accumulated in the pepper fruits. MeJA can enhance the capsaicinoid production. Temporal and spatial expression of capsaicinoid biosynthetic genes are helpful to understand the molecular mechnism of capsaicinoid biosynthesis in the fruits of pepper. Although some of the capsaicinoid biosynthetic genes in pepper have been identified, the expression of these genes at different developing stages of fruit has not been systemically investigated, and little is known about the molecular basis of MeJA inducing capsaicinoid biosynthesis. Results: HPLC study revealed that the capsaicinoid accumulation in the developing fruit of pepper initially appeared at 24 DAP (day after pollination), was actively development at 36 DAP and peaked at 48 DAP. 11 genes that encoded enzymes involved in capsaicinoid biosynthesis were isolated and characterized. Gene expression with quantitative reverse-transcription polymerase chain reaction analysis demonstrated that the CaCS was unique expressed in placenta and the other 10 genes were expressed in all selected tissues and 9 of 11 genes (except CaCa4H and CaCa3H) were strongly expressed in placenta tissue. Spatial expression analysis demostrated that the 11 gene could be collectively grouped into four categories based on the patterns of relative expression of the genes during fruit development. Category I has 2 and they displayed a bell-shaped expression pattern with the peak expression at 24 DAP, Category II contains 5 genes and expression of the 5 genes was constantly increased from 0 to 36 DAP and peaked at 36 DAP. Category III comprises of 2 genes and both genes reached the peak at 48 DAP. Category IV consists of 2 genes and they showed a high expression at 36 and 48 DAF, but unexpressed from 0 to 12 DAP. The gene expressions of the 11 genes were up-regulated by MeJA. 3 genes showed a high expression at 24 h; 4 genes reached the peak at 12 h; the top expression were observed at 18 h; The last one, CaACYase, achieved the highest level at 8 h. Conclusion: The biosynthesis of capsaicinoid in pepper fruit is developmentally regulated. The expression of the majority of capsaicinoid biosynthetic genes is highly consistent with the development accumulation of capsaicinoid in pepper fruit. These results not only provide the initial information on spatial and temporal expression of capsaicinoid biosynthetic genes in pepper developing fruit, but are also valuable to identify the MeJA-induced genes for capsaicinoid biosynthesis and accumulation during pepper fruit development.

Jasmonates (JAs), including jasmonic acid (JA) and its biologically active derivative JA-Ile, are lipid-derived plant signalling molecules. They govern plant responses to stresses, such as wounding and insect herbivory. Wounding elicits a rapid increase of JA and JA-Ile levels as well as the expression of JAR1, coding for the enzyme involved in JA-Ile biosynthesis. Endogenous increase and application of JAs, such as MeJA, a JA methylester, result in increased defence levels, often accompanied by diminished growth. The function of jarin-1 in Arabidopsis thaliana was assessed. To investigate whether jarin-1 does function similarly in other plants, we tested this in Medicago truncatula, Solanum lycopersicum, and Brassica nigra seedlings in a root growth inhibition assay. Application of jarin-1 alleviated the inhibition of root growth after MeJA application in M. truncatula seedlings, proving that jarin-1 is biologically active in M. truncatula. Jarin-1 did not show, however, a similar effect in S. lycopersicum and B. nigra seedlings treated with MeJA. Even JA-Ile levels were not affected by application of jarin-1 in wounded leaf disks from S. lycopersicum. Based on these results, we conclude that the effect of jarin-1 is highly species-specific. Researchers intending to use jarin-1 for studying the function of JAR1 or JA-Ile in their model plants, must test its functionality before use.

Sporisorium scitamineum, the basidiomycetous fungus causing sugarcane smut that leads to severe losses in sugarcane quantity and quality, undergoes sexual mating to form dikaryotic hyphae capable of invading the host cane. Therefore, suppressing dikaryotic hyphae formation would potentially be an effective way to prevent host infection by the smut fungus, and the following disease symptom development. The phytohormone methyl jasmonate (MeJA) has been showed to induce plant defense against insects and microbial pathogens. In this study, we verified that exogenous addition of MeJA suppressed dikaryotic hyphae formation under in vitro culture condition, and effective in inhibiting maize smut disease symptom caused by Ustilago maydis. We constructed an Escherichia coli strain expressing plant JMT gene, encoding a jasmonic acid carboxyl methyl transferase that catalyzes conversion from jasmonic acid (JA) to MeJA. By GC-MS we confirmed that the transformed E. coli strain, designated as pJMT strain, was able to produce MeJA in the presence of JA and S-adenosylmethionine (SAM; as methyl donor). Furthermore, the pJMT strain was able to suppress S. scitamineum filamentous growth under in vitro culture condition. It waits to further optimize JMT expression under field condition, in order to utilize the pJMT strain as a biocontrol agent (BCA) of sugarcane smut disease. Overall, our study provides a potentially novel method for controlling crop fungal diseases by boosting phytohormone biosynthesis.