Early Methyl Jasmonate Application to Peach Delays Fruit/Seed Development by Altering the Expression of Multiple Hormone-Related Genes

Jasmonates (JAs) play a role in the responses to environmental stress and during growth processes, including fruit/seed development. To better understand the molecular basis of the developmental control exerted by JAs in fruit and seed, methyl jasmonate (MJ, 0.80 mM) was applied to peach fruit (Prunus persica var. laevis Gray) at an early (S1) developmental stage and under field conditions. Mesocarp and seed were sampled at time intervals until ripening; at harvest, MJ-treated fruit were less ripe than controls as assessed by a nondestructive device called a DA-meter. Real-time reverse-transcription polymerase chain reaction analyses revealed that JA-related gene expression (AOS1 and JAZs) was affected early (24 h) after treatment, whereas peaks in transcript accumulation of mesocarp (CYCD3, RD22, SP, Aux/IAA) and seed (PRP, SSADH, PRU, LEA) developmental marker genes were shifted in accord with a developmental slowing down. At ripening (S4), in the mesocarp the upregulation of the ethylene biosynthetic genes ACO1 and ACS1 and of the softening-related genes PG and EXP2 was dramatically counteracted by MJ. Ethylene signaling (ETR1, ETR2) was also affected. Because JAs cross-talk with other hormones, the transcript amounts of major hormone-related genes such as GH3, IAA-AH, NCED, and GA2ox were evaluated and showed changes that further support the hypothesis of delay of the developmental program.