Characterizing ethylene pathway genes during the development, ripening, and postharvest response in Citrus reticulata Blanco fruit pulp

Abstract

Ethylene is involved in the regulation of the natural process of fruit pulp development and postharvest storage. The presentstudy was carried out to determine the expression of eight genes encoding ethylene biosynthesis and signaling during developmentin Khasi mandarin (Citrus reticulata Blanco) fruit pulp as well as during postharvest storage in the fruit pulp (at 4 °C and 20 °C).Gibberellic acid (GA3) is known to improve internal fruit quality and to mediate various stress responses during postharvest fruit storagein species like citrus. The effect of GA3 during postharvest storage was also investigated to understand the regulation of the ethylenegenes on its own biosynthesis and signaling. The results suggest that 1-aminocyclopropane-1-carboxylate synthase-2 (ACS2), ethyleneresponse sensor-1 (ERS1), constitutive triple response-1 (CTR1), and ethylene insensitive 3-like-1(EIL1) have a physiological role in theripening of Khasi mandarin fruit pulp. 1-Aminocyclopropane-1-carboxylate synthase-1 (ACS1), ethylene response-1 (ETR1), and ethyleneinsensitive-2 (EIN2) were found to be developmentally regulated in immature fruit pulp, suggesting their role in rapid growth of thefruit pulp. Postharvest storage at 4 °C and 20 °C influenced the expression of different ethylene-related genes during ripening in Khasimandarin fruit pulp. Cold storage (4 °C) markedly triggered the transcription of ethylene biosynthetic genes, especially ACS1 and ACS2in the fruit pulp. Exogenous application of GA3 enhanced cold tolerance especially at the transcript level of ACS1, ACS2, ETR1, and ERS1genes in the pulp of Khasi mandarin fruit during cold storage when harvested at the full maturity stage.