Novel Protein-Protein Inhibitor Based Approach to Control Plant Ethylene Responses: Synthetic Peptides for Ripening Control

Abstract

Ethylene signaling is decisive for many plant developmental processes. Among these, control of senescence, abscission and fruit ripening are of fundamental relevance for global agriculture. Consequently, detailed knowledge of the signaling network along with the molecular processes of signal perception and transfer are expected to have high impact on future food production and agriculture. Recent advances in ethylene research have demonstrated that signaling of the plant hormone critically depends on the interaction of the ethylene receptor family with the NRAMP-like membrane protein ETHYLENE INSENSITIVE 2 (EIN2) at the ER membrane, phosphorylation-dependent proteolytic processing of ER-localized EIN2 and subsequent translocation of the cleaved EIN2 C-terminal polypeptide (EIN2-CEND) to the nucleus. EIN2 nuclear transport, but also interaction with the receptors sensing the ethylene signal, both, depend on a nuclear localization signal (NLS) located at the EIN2 C-terminus. Loss of the tight interaction between receptors and EIN2 affects ethylene signaling and impairs plant ethylene responses. Synthetic peptides derived from the NLS sequence interfere with the EIN2–receptor interaction and have utility in controlling plant ethylene responses such as ripening. Here, we report that a synthetic peptide (NOP-1) corresponding to the NLS motif of Arabidopsis EIN2 (aa 1262–1269) efficiently binds to tomato ethylene receptors LeETR4 and NR and delays ripening in the post-harvest phase when applied to the surface of sampled green fruits pre-harvest. In particular, degradation of chlorophylls was delayed by several days, as monitored by optical sensors and confirmed by analytical methods. Similarly, accumulation of β-carotene and lycopene in the fruit pulp after NOP-1 application was delayed, without having impact on the total pigment concentration in the completely ripe fruits. Likewise, the peptide had no negative effects on fruit quality. Our molecular and phenotypic studies reveal that peptide biologicals could contribute to the development of a novel family of ripening inhibitors and innovative ripening control in climacteric fruit.

Influence of the ethylene‐related signal‐inhibiting octapeptide NOP‐1 on postharvest ripening and quality of ‘Golden Delicious’ apples

“…Recent studies have confirmed the effectiveness of the NLS‐derived octapeptide NOP‐1 to delay tomato ripening . Owing to the homology of the ethylene receptors and the ubiquitous presence of the NLS motif in the plant kingdom, it is likely that the ripening inhibition effects of NOP‐1 can also apply to other climacteric fruits .…”

“…The maturity development of climacteric fruit is controlled by the plant hormone ethylene . Via activation of ethylene receptors at the endoplasmic reticulum membrane, a signalling cascade leads to an activation of ripening‐related genes . This induces changes in fruit colour, flesh firmness, aroma and texture as chlorophyll, cellulose and pectin are broken down and carotenoids and aroma volatiles are produced .…”

“…The synthetic peptide NOP‐1 (LKRYKRRL) inhibits the interaction of the ethylene receptor ETR1 and EIN2. NOP‐1 has been shown to be effective in delaying the ripening process in tomato without fruit quality impairment . The NLS‐motif and the ETR are highly conserved in the plant kingdom .…”

“…The NLS‐motif and the ETR are highly conserved in the plant kingdom . Consequently, NOP‐1 seems to be a promising opportunity to investigate the control of ripening in other climacteric fruit, such as apples …”

“…To explore the efficacy of NOP‐1 for ripening control in apples, we first tested binding of NOP‐1 to the isolated purified ethylene receptor MdETR1 from Malus domestica , which shares about 42–84% sequence identity with the corresponding tomato receptors LeETR4, NR and LeETR1 …”