Unraveling the induction of phytoene synthase 2 expression by salt stress and abscisic acid in Daucus carota.

Kevin Simpson,Rodrigo Contreras,Carlos Flores-Ortiz,Claudia Stange,Michael Handford,Luis Felipe Quiroz-Iturra,Paulina Fuentes

doi:10.1093/jxb/ery207

Kevin Simpson, Rodrigo Contreras + Show 5 more

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https://doi.org/10.1093/jxb/ery207

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Abstract

Phytoene synthase (PSY) is the first committed enzyme of the carotenoid biosynthesis pathway and the most important point of regulation. Carotenoids are precursors of abscisic acid (ABA), which mediates abiotic stress tolerance responses in plants. ABA activates the synthesis of its own precursors through induction of PSY expression. Carrot, a species that accumulates very high amounts of carotenoids in its reserve root, has two PSY paralog genes that are expressed differentially in the root. Here, we determined that DcPSY2 expression is induced by salt stress and ABA. A DcPSY2 promoter fragment was obtained and characterized. Bioinformatic analysis showed the presence of three ABA responsive elements (ABREs). Through overexpressing pPSY2:GFP in Nicotiana tabacum we determined that all three ABREs are necessary for the ABA response. In the carrot transcriptome, we identified three ABRE binding protein (DcAREB) transcription factor candidates that localized in the nucleus, but only one, DcAREB3, was induced under ABA treatment in carrot roots. We found that AREB transcription factors bind to the carrot DcPSY2 promoter and transactivate the expression of reporter genes. We conclude that DcPSY2 is involved in ABA-mediated salt stress tolerance in carrot through the binding of AREB transcription factors to its promoter.

Highlights

Carotenoids are colored lipid-soluble molecules that act as accessory pigments and have photoprotective functions during photosynthesis (Telfer, 2005; Stange and Flores, 2012)
Salt stress induces the expression of DcPSY1 and DcPSY2 and the synthesis of abscisic acid (ABA) in carrot leaves and roots but only DcPSY2 expression is induced by ABA
In order to determine if the Phytoene synthase (PSY) paralog genes in carrot respond differentially to abiotic stress, as was reported previously in other species,4-week-old carrot seedlings were treated with 250 mM NaCl and the expression levels of DcPSY1 and DcPSY2 were measured in leaves and roots

Summary

Introduction

Carotenoids are colored lipid-soluble molecules that act as accessory pigments and have photoprotective functions during photosynthesis (Telfer, 2005; Stange and Flores, 2012). They protect cells from excessive light energy through thermal dissipation and supply substrates for the biosynthesis of the plant growth regulator abscisic acid (ABA) (Crozier et al, 2000) and of strigolactones (Moreno Beltran and Stange, 2016). One of the most prevalent and important mechanisms is the regulation of the expression of genes involved directly in the synthesis of carotenoids (Cazzonelli and Pogson, 2010), which is influenced by external and developmental factors such as light, fruit ripening, biotic and abiotic stress, negative–positive feedback mechanisms, and in response to hormones (Lu and Li, 2008)

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