The JA pathway is rapidly down-regulated in petal abscission zones prior to flower opening and affects petal abscission in fragrant roses during natural and ethylene-induced petal abscission

Organ abscission is a developmental process regulated through changes in the abscission zone (AZ) and governed primarily by ethylene. In roses, the opening of flowers is also an ethylene-sensitive process possibly requiring changes at the AZ to facilitate petal movement. A study of the rose petal AZ transcriptome of the early-abscising fragrant rose, R. bourboniana, had indicated suppression of the jasmonic acid (JA) pathway in the AZ before abscission. Detailed investigation of 24 genes representing JA biosynthesis/perception/signalling revealed a rapid and substantial down-regulation of the entire JA pathway in the AZ prior to flower opening and abscission. Transcript levels of 17 genes encoding JA biosynthesis members of the PLD/LOX/AOS/AOC/OPR families and the receptor/signalling components of COI1/JAZ/MYC2/NINJA families decreased by 50–90% in petal AZ within 4 h of ethylene treatment as well as during natural field abscission (ethylene untreated). In contrast, R. hybrida flowers (which show delayed opening and abscission even after ethylene treatment) were much less affected in 10/24 genes while transcript levels of 9/24 JA pathway genes actually increased several fold during or just prior to abscission. JA treatment delayed flower opening as well as petal abscission by more than 24 h in R. bourboniana and also increased transcription of the JA pathway genes, unlike ethylene. The strong and rapid reduction of the entire JA pathway in the AZ in R. bourboniana flowers, prior to flower opening and petal abscission, suggests a negative role for JA in these processes with JA acting opposite to ethylene and possibly reducing ethylene sensitivity.