Exogenous MeJA modulates postharvest tomato aroma by suppressing JAs-ethylene signaling crosstalk

Xuehui Li¹Xiaoyu Tan²Gao Yubang¹Xinyu Luo³Dongguang Xu¹Yiting Wang³Xinli Geng⁴Xiaolin Yang⁵Yuhua Xie⁶Qiuhong Niu^1*Xiaopu Ren^2*Libin Wang^7*

• ¹Nanyang Normal University, Nanyang, China
• ²Nanjing Agricultural University College of Horticulture, Nanjing, China
• ³Shandong Agricultural University College of Resources and Environment, Tai'an, China
• ⁴Xinjiang Academy of Agricultural Sciences, Urumqi, China
• ⁵China Agricultural University, Beijing, China
• ⁶Hezhou University, Hezhou, China
• ⁷Nanjing Agricultural University, Nanjing, China

Until recently, the mechanism on methyl jasmonate (MeJA)-mediated suppression of ethylene metabolism and thus quality formation in the ripening tomato has not been fully clarified. In this study, exogenous application of MeJA at the breaker stage suppressed endogenous jasmonates (JAs), especially jasmonoyl-isoleucine (JA-Ile) by 13%, and ethylene production by 33% in the red 'FL 47' tomato. Meanwhile, the activities of lipoxygenase (LOX), allene oxide cyclase (AOC), allene oxide synthase (AOS), 12-oxo-phytodienoic reductase (OPR), 1-aminocyclopropane-1-carboxylate oxidase (ACO), and 1-aminocyclopropane-1-carboxylate synthase (ACS) in their metabolic pathways in the MeJA-treated tomato were reduced to over 87% of control fruit; and the mRNAs abundances of SlLOXD, SlAOC, SlAOS, SlOPR3, SlACO1, SlACS2, SlACS4, SlMYC2, MEDIATOR 25 (SlMED25), ETHYLENE RESPONSE (SlETR3), SlETR4, SlETR7, ETHYLENE INSENSITIVE 2 (SlEIN2), ETHYLENE INSENSITIVE3-LIKE 1 (SlEIL1), EIN3-BINDING F-BOX PROTEIN 1 (SlEBF1), SlEBF2, and ETHYLENE RESPONSE FACTOR 1 (SlERF1) suffered 17-30% reduction after MeJA fumigation. Additionally, the production of sugars, organic acids and 21 volatiles was changed by exogenous MeJA treatment, causing the alteration of flavor profile. Moreover, the MeJA-induced reduction of six key volatiles (geranyl acetone, 1-penten-3-one, 6-methyl-5-hepten-2-one, 2-methyl butanal, 3-methyl butanal, and 3-methyl butanol), whose generation was regulated by ethylene, was concomitant with the suppressed gene expression levels and substrate contents in their biosynthesis pathways. The mRNAs abundances of SlLOXC, PHYTOENE SYNTHASE 1 (SlPSY1), CAROTENOID CLEAVAGE DIOXYGENASE 1A (SlCCD1A), SlCCD1B, and BRANCHED-CHAIN AMINO ACID AMINOTRANSFERASE 1 (SlBCAT1) suffered 19-29% reduction by MeJA treatment; and the contents of phytoene, phytofluene, trans-lycopene, γ-carotenoid, β-carotenoid, linoleic and linolenic acid in the MeJA-fumigated tomato were over 74% of those in control fruit. By considering the positive relationship between endogenous JA-Ile and ethylene levels in the ripening fruit, our results implied that the MeJA-mediated aroma profile change in the red 'FL 47' tomato fruit might be due to the mitigated endogenous JAs (especially JA-Ile) and ethylene biosynthesis & signaling transduction processes.