Expression of Ripening-Related Genes as Affected by Chilling in Tomato

The effects of chilling on the expression of ripening-related genes has been studied in a tomato (Solanum lycopersicum ´ S. pennelli) introgression line (IL 11-2).  Tomato fruit were harvested at breaker stage of maturity and ripened at 20 ^oC for 0 to 14 d, or stored at 3 ^oC for up to 4 weeks, and then ripened at 20 ^oC. Climacteric ethylene production was increased in fruit stored for 1 week, but reduced in fruit stored for 4 weeks.  Fruit ripening was delayed or inhibited in fruit stored for 2 and 4 weeks as assessed by red color development and softening at 20 °C.  The expression of genes involved in color development, phytoene synthase1 (PSY1), carotenoid isomerase (CRTISO), geranylgeranyl diphosphate synhase 2 (GGPPS2), and 1-deoxy-D-xylulose-5-phosphate synthase (DXS), were reduced by chilling, as was polygalacturonse (PG), pectin esterase1 (PE1), β-galacturonase (TBG4), expansin ( LeExp1), and xyloglucan endotransglucosylase/ hydrolase 5 (XTH5), associated with cell wall-modification, as well as alcohol dehydrogenase 2 (ADH2) and alcohol acyltransferase (AAT). Fruit stored for 1 week showed an increased or unchanged gene expression of aminocyclopropane-1-carboxylate synthase genes ACS2, ACS4, whereas reduced ACS2 and ACS4 expression was observed in fruit stored for 4 weeks.  ACO1 expression increased in chilled fruit during cold storage, but decreased after removal to 20 °C.  Fruit stored for 1 and 2 weeks showed a transient increase in NR expression, while the reduced NR expression was observed in fruit stored for 4 weeks through ripening. In contrast, LeETR1 was induced by chilling during cold storage, and then decreased after removal to 20 °C.  Reduced LeETR4 expression was observed in fruit stored for 4 weeks, while fruit stored for 1 and 2 weeks showed slightly reduced LeETR4 during early state of ripening.  The expression of LeCTR1 was induced during cold storage, but the expression levels decreased after removal to 20 °C.  The expression of LeMADS-RIN, encoding a ripening-specific transcription factor Le-MADS-RIN, was increased after 1 week of cold storage but was reduced after 4 weeks.  Fruit stored for 4 weeks showed reduced LeMADS-RIN expression during ripening, while fruit stored for 1 week showed reduced LeMADS-RIN after 3 d of ripening.