Differential fine-tuning of gene expression regulation in coffee leaves by CcDREB1D promoter haplotypes under water deficit.

Gabriel Sergio Costa Alves,Luana Ferreira Torres,Hervé Etienne,Jean-Christophe Breitler,Frédéric Gatineau,Pierre Marraccini,Benoît Bertrand,Alan Carvalho Andrade,Thierry Joët,Eveline Déchamp

doi:10.1093/jxb/erx166

Abstract

Despite the importance of the DREB1D gene (also known as CBF4) in plant responses to water deficit and cold stress, studies analysing its regulation by transgenic approaches are lacking. In the current work, a functional study of three CcDREB1D promoter haplotypes (named HP15, HP16 and HP17) isolated from drought-tolerant and drought-sensitive clones of Coffea canephora was carried out in plants of C. arabica stably transformed by Agrobacterium tumefaciens by analysing their ability to regulate the expression of the uidA reporter gene in response to water deficit mimicked by polyethylene glycol (-2.0 MPa) and low relative humidity treatments. A deletion analysis of their corresponding 5'-upstream regions revealed increased specificity of β-glucuronidase activity in the polyethylene glycol and low relative humidity treatments, with high expression in leaf mesophyll and guard cells in full-length constructs. RT-qPCR assays also revealed that the HP16 haplotype (specific to clone tolerant to water deficit) had stronger and earlier activity compared with the HP15 and HP17 haplotypes. As most of the cis-regulatory elements involved in ABA-dependent and -independent networks, tissue specificity and light regulation are common to these haplotypes, we propose that their organization, as well as the nucleic acid polymorphisms present outside these boxes, may play a role in modulating activities of DREB1D promoters in guard cells.

Highlights

Climate change is leading to increasingly extreme temperatures and drought periods, which are major abiotic factors affecting coffee production (DaMatta and Ramalho, 2006)
We investigated the responses of different haplotypes of the CcDREB1D (CBF4) promoters of C. canephora to polyethylene glycol (PEG) and low relative humidity (RH) treatments by analysing their ability to regulate the expression of the uidA reporter gene in stably transformed C. arabica plants
The results presented here indicate that the HP15, HP16 and HP17 haplotypes of CcDREB1D promoters harbored several abiotic stress-responsive cis-regulatory element (CRE) in common, including those involved in tissue-specific and light regulation

Summary

Introduction

Climate change is leading to increasingly extreme temperatures and drought periods, which are major abiotic factors affecting coffee production (DaMatta and Ramalho, 2006). Increased [CO2] in air is a key factor for coffee plant acclimation to high temperature, strengthening the photosynthetic pathway, metabolism and antioxidant protection, and modifying gene transcription and mineral balance (Ramalho et al, 2013; Martins et al, 2014, 2016; Ghini et al, 2015; Rodrigues et al, 2016). In this context, understanding the genetic determinism of coffee’s adaptation to climate change has become essential for creating new varieties (Cheserek and Gichimu, 2012; van der Vossen et al, 2015)

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