Ethylene Response of Plum ACC Synthase 1 (ACS1) Promoter is Mediated through the Binding Site of Abscisic Acid Insensitive 5 (ABI5).

Avi Sadka,Jianrong Feng,Yunting Zhang,David Toubiana,Lyudmila Shlizerman,Eduardo Blumwald,Qiaoping Qin,Macarena Farcuh

doi:10.3390/plants8050117

Abstract

The enzyme 1-amino-cyclopropane-1-carboxylic acid synthase (ACS) participates in the ethylene biosynthesis pathways and it is tightly regulated transcriptionally and post-translationally. Notwithstanding its major role in climacteric fruit ripening, the transcriptional regulation of ACS during ripening is not fully understood. We studied fruit ripening in two Japanese plum cultivars, the climacteric Santa Rosa (SR) and its non-climacteric bud sport mutant, Sweet Miriam (SM). As the two cultivars show considerable difference in ACS expression, they provide a good system for the study of the transcriptional regulation of the gene. To investigate the differential transcriptional regulation of ACS1 genes in the SR and SM, their promoter regions, which showed only minor sequence differences, were isolated and used to identify the binding of transcription factors interacting with specific ACS1 cis-acting elements. Three transcription factors (TFs), abscisic acid-insensitive 5 (ABI5), GLABRA 2 (GL2), and TCP2, showed specific binding to the ACS1 promoter. Synthetic DNA fragments containing multiple cis-acting elements of these TFs fused to β-glucuronidase (GUS), showed the ABI5 binding site mediated ethylene and abscisic acid (ABA) responses of the promoter. While TCP2 and GL2 showed constant and similar expression levels in SM and SR fruit during ripening, ABI5 expression in SM fruits was lower than in SR fruits during advanced fruit ripening states. Overall, the work demonstrates the complex transcriptional regulation of ACS1.

Highlights

Climacteric fruit ripening is characterized by a burst in respiration rates and increased levels of autocatalytic ethylene production [1,2]
Analysis by PlantPAN showed that the promoter comprised several cis-acting regulatory elements, including those associated with the response(s) to abscisic acid (ABA), ethylene, and gibberellins, as well as light responsiveness (Table S3)
Since ACS1 and ACS3 transcripts in Sweet Miriam fruits, the non-climacteric mutant of Santa Rosa (SR), were remarkably lower than those in SR, and this reduction correlated well with their low ethylene contents [34], we investigated whether differences in the ACS1 promoter region could explain the reduced ACS1 expression

Summary

Introduction

Climacteric fruit ripening is characterized by a burst in respiration rates and increased levels of autocatalytic ethylene production [1,2]. In non-climacteric fruits, respiration declines gradually and there is no increase in ethylene production, ethylene might play a role in various aspects of fruit maturation. Ethylene biosynthesis starts by the conversion of methionine into. Plants 2019, 8, 117 of 1-amino-cyclopropane-1-carboxylic acid (ACC) by ACC synthase (ACS) and its conversion into ethylene by ACC oxidase (reviewed in [3,4]). The reaction catalyzed by ACS is a rate-limiting step in ethylene biosynthesis, ACS plays an important role in different aspects of plant development and the responses to environmental cues. Epigenetic regulation might play a role in ACS expression [14]

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Conclusion