Abstract

Developmentally, ripening is associated with metabolic and texture changes in fruits, whilst senescence is a way to remobilize resources for their use elsewhere. As an oxidative process, senescence can be temporarily delayed by adding antioxidants to neutralize ROS. In the plant, ripening and senescence are tightly regulated, and ethylene is the main hormone responsible for their induction. Ethylene is made from S-adenosylmethionine (SAM), a substrate also used by lipoyl synthase (LIP1), a Senescence Associated Gene, whose expression rises during this process. LIP1 is required in the synthesis of lipoic acid, a powerful antioxidant that is also a cofactor of key enzymes in primary metabolism and plays a role in abiotic stress tolerance. We aim to dissect the interplay of the usage of SAM using LIP1 as a lever. To do so, we identified and functionally characterized LIP1 from tomato (SlLIP1) at the molecular and biochemical levels. We stably-transformed plants with SlLIP1 under the control of a constitutive (35S), and a fruit-specific (PG) promotor, and are developing tools to up- and down-regulate its expression in a more fine-tuned manner. Our results show that SlLIP1 has the molecular characteristics of a lipoyl synthase, is located in the mitochondria, heterologously complements a bacteria lipoyl synthase mutant, and is ubiquitously expressed, especially in fruits. SlLIP1 overexpression increases lipoylation levels and spraying tomato plants with lipoic acid increases their tolerance to saline stress and delays leaf senescence. However, when expressed constitutively, plants suffer delayed development, especially at the reproductive phase, yet when expression is confined to fruits, plants develop normally. Interestingly, ethylene levels were higher in developing fruits, indicating a misbalance of SAM usage, and metabolomic analyses reveal modifications in primary metabolites in these organs. Funding: Fondecyt 1231417 (MH), ACT210025 (MH), Fundación María Ghilardi Venegas (MPC, PC) and ANID Doctoral Scholarship (21210768, FU).