Roles of RIN and ethylene in tomato fruit ripening and ripening‐associated traits

Abstract

Summary RIPENING INHIBITOR (RIN)‐deficient fruits generated by CRISPR/Cas9 initiated partial ripening at a similar time to wild‐type (WT) fruits but only 10% WT concentrations of carotenoids and ethylene (ET) were synthesized. RIN‐deficient fruit never ripened completely, even when supplied with exogenous ET. The low amount of endogenous ET that they did produce was sufficient to enable ripening initiation and this could be suppressed by the ET perception inhibitor 1‐MCP. The reduced ET production by RIN‐deficient tomatoes was due to an inability to induce autocatalytic system‐2 ET synthesis, a characteristic feature of climacteric ripening. Production of volatiles and transcripts of key volatile biosynthetic genes also were greatly reduced in the absence of RIN. By contrast, the initial extent and rates of softening in the absence of RIN were similar to WT fruits, although detailed analysis showed that the expression of some cell wall‐modifying enzymes was delayed and others increased in the absence of RIN. These results support a model where RIN and ET, via ERFs, are required for full expression of ripening genes. Ethylene initiates ripening of mature green fruit, upregulates RIN expression and other changes, including system‐2 ET production. RIN, ET and other factors are required for completion of the full fruit‐ripening programme.

Phytohormones in fruit development and maturation

“…while, in tomato, JA influences polyamine levels and SlSAMT catalyzes the biosynthesis of SA into methyl salicylate to enhance the taste of ripe fruit (Tieman et al ., 2010; Kumar et al ., 2014). An exciting and currently expanding area of inquiry pertains to the genetic understanding of the accumulation of flavor and aroma volatiles (Tieman et al ., 2017; Gao et al ., 2019a, 2019b; Li et al ., 2020a, 2020b) and, while plant hormones likely play a role in their production, this is an area open to further exploration.…”

A nuclear-localized cysteine desulfhydrase plays a role in fruit ripening in tomato

“…Our data show that the cell wall metabolism-related enzymes CEL2, EXP, XTH5, PG, and TBG4, the ethylene biosynthesis-related genes ACO1, ACO3, and ACS2, and the ethylene responsive genes E4 and E8 were all expressed at significantly higher levels in lcd1-7 than in wild-type tomato fruit. RIN, a MADS-box family transcription factor, and Nor, a NAC family transcription factor, are TFs that have been shown to be important in regulating ethylene biosynthesis and fruit ripening [26][27][28] . We found that the expression levels of RIN and Nor increased significantly at the beginning of fruit ripening in WT tomato, but significantly higher gene expression was found in lcd1.…”

Overexpression of MdARD4 Accelerates Fruit Ripening and Increases Cold Hardiness in Tomato

“…RNA interference of SlACS2 in tomato fruits repressed ethylene production and fruit ripening [ 39 ]. Additionally, RIPENING INHIBITOR (RIN) and ethylene, via ethylene response factors (ERFs), are required for the complete expression of ripening genes such as E4 and E8 , the classic ethylene-induced genes [ 8 ]. ERFs regulate ethylene-dependent transcription and ethylene-inducible gene expression that play an important role in ripening [ 5 , 7 , 38 , 40 , 41 , 42 , 43 , 44 ].…”

“…Naeem et al identified that SmCOP1 (CONSTITUTIVE PHOTOMORPHOGENIC) regulates ethylene biosynthesis and affects fruit ripening in tomato [ 4 ]. Studies have also shown that ethylene triggers fruit ripening via the ethylene signaling pathway [ 5 , 6 , 7 , 8 ].…”