Localisation and expression of zeaxanthin epoxidase mRNA in Arabidopsis in response to drought stress and during seed development

Abstract

Abscisic acid (ABA) is involved in seed development and plant adaptation to environmental stresses. ABA is synthesized from cleaved xanthophylls and zeaxanthin epoxidase (ZEP) is the enzyme responsible for the conversion of zeaxanthin to violaxanthin. In this study, we have characterized the ABA1 gene (AtZEP) of Arabidopsis thaliana L. and show that this complements the aba1 mutant, defective in zeaxanthin epoxidation. The molecular basis for two aba1 mutant alleles has been determined and the reduction in their AtZEP transcript levels correlates with the molecular defect identified. As AtZEP mRNA abundance was not affected in two other ABA-deficient mutants (aba2 and aba3) and in two ABA-insensitive mutants (abi1 and abi2), no feedback regulation of ABA biosynthesis seems to occur at the level of ZEP transcription. Steady state transcript levels increased in roots during rapid water stress as well as progressive drought stress, providing evidence that zeaxanthin epoxidation contributed to the regulation of ABA biosynthesis in roots and consequently to the plant adaptive response to hydric stress. In seeds in situ hybridization analysis detectedAtZEP mRNA in the embryo cells from the globular stage to desiccation phase. In contrast, expression of AtZEP in maternal tissues was specific to the maturation phase. These results are discussed in relation to the role of ABA both in response to drought stress and in seed development.

Regulation of carotenoid and ABA accumulation during the development and germination of Nicotiana plumbaginifolia seeds

“…In both species, ZEP transcripts and proteins are highly abundant in photosynthetic tissues, as compared to roots or seeds. Furthermore, unlike in leaves, a good correlation between ABA accumulation and ZEP gene expression has been observed in seeds and in water-stressed roots (Audran et al 1998(Audran et al , 2001Frey et al 1999). The enzymatic steps leading from t-violaxanthin to the formation of cis-isomers of violaxanthin and neoxanthin have not yet been clearly identified (Nambara and Marion-Poll 2005).…”

“…The transformation vector pKYLX71-35S2 had been used to clone a full-length AtZEP cDNA in the sense orientation under the control of the 35S promoter and upstream of an rbcS 3¢ region (Audran et al 2001). The 35S promoter was removed by EcoRI-HindIII digestion and replaced after filling cohesive ends by a 2.9 kb blunt ended fragment (HindIII-NcoI) of the Brassica napus isocitrate lyase promoter (pICL) (Zhang et al 1994).…”

“…Seed RNAs were extracted as described by Dean et al (1985). Northern blots were hybridized with either a labelled HindIII internal fragment (1.4 kb) of NpZEP cDNA, or a full-length AtZEP cDNA probe as previously described (Frey et al 1999;Audran et al 2001). RNA extractions and hybridizations were repeated independently at least twice.…”

“…The conversion of zeaxanthin into trans-violaxanthin is catalyzed by ZEP. The corresponding gene was first cloned from Nicotiana plumbaginifolia, after insertional mutagenesis, and called NpABA2 or NpZEP, then in Arabidopsis thaliana (AtABA1 or AtZEP) (Marin et al 1996;Audran et al 2001;Xiong et al 2002). In both species, ZEP transcripts and proteins are highly abundant in photosynthetic tissues, as compared to roots or seeds.…”

Abscisic Acid Regulates Early Seed Development in Arabidopsis by ABI5-Mediated Transcription of SHORT HYPOCOTYL UNDER BLUE1

“…For instance, AB-SCISIC ACID DEFICIENT1 (ABA1) encodes a zeaxanthin epoxidase that functions in ABA biosynthesis and is expressed ubiquitously in Arabidopsis seed (Audran et al, 2001). The enzymes 9-cisepoxycarotenoid dioxygenases catalyze the cleavage of 9-cisepoxycarotenoids to xanthoxin, the key regulatory step in ABA biosynthesis.…”