The tomato mutation nxd1 reveals a gene necessary for neoxanthin biosynthesis and demonstrates that violaxanthin is a sufficient precursor for abscisic acid biosynthesis

Abstract

SUMMARYCarotenoid pigments are indispensable for plant life. They are synthesized within plastids where they provide essential functions in photosynthesis. Carotenoids serve as precursors for the synthesis of the strigolactone phytohormones, which are made from b-carotene, and of abscisic acid (ABA), which is produced from certain xanthophylls. Despite the significant progress that has been made in our understanding of the carotenoid biosynthesis pathway, the synthesis of the xanthophyll neoxanthin has remained unknown. We report here on the isolation of a tomato (Solanum lycopersicum) mutant, neoxanthin-deficient 1 (nxd1), which lacks neoxanthin, and on the cloning of a gene that is necessary for neoxanthin synthesis in both tomato and Arabidopsis. The locus nxd1 encodes a gene of unknown function that is conserved in all higher plants. The activity of NXD1 is essential but cannot solely support neoxanthin synthesis. Lack of neoxanthin does not significantly reduce the fitness of tomato plants in cultivated field conditions and does not impair the synthesis of ABA, suggesting that in tomato violaxanthin is a sufficient precursor for ABA production in vivo.

Ethylene Responses in Rice Roots and Coleoptiles Are Differentially Regulated by a Carotenoid Isomerase-Mediated Abscisic Acid Pathway

“…b-Carotene, which serves as a precursor for the plant hormone strigolactone (SL), can be further metabolized to b,b-xanthophylls such as zeaxanthin (Nambara and Marion-Poll, 2005;Xie et al, 2010). ABA is produced from violaxanthin or neoxanthin through several enzymatic reactions, including 9-cis-epoxycarotenoid dioxygenase (NCED), neoxanthin-deficient 1, alcohol dehydrogenase (ABA2)/ short-chain dehydrogenase/reductase, abscisic aldehyde oxidase (AAO3), and sulfurated molybdenum cofactor sulfurase (ABA3) (Nambara and Marion-Poll, 2005;Finkelstein, 2013;Neuman et al, 2014).…”

Use of Natural Diversity and Biotechnology to Increase the Quality and Nutritional Content of Tomato and Grape

“…The carotenoid pathway, for example, is one of the best elucidated metabolism in tomato fruit due to the availability of a series of well-characterized mutations (Figure 1). These mutants provide distinct berry color phenotypes: apricot, at , loss of function in the isopentenyl diphosphate 1 ( ID11 ) gene (Pankratov et al, 2016); yellow flesh, r , knockout of the phytoene synthase 1 ( PSY1 ) gene (Fray and Grierson, 1993); tangerine, t , loss of function in the carotenoid isomerase 1 (CrtISO1) enzymatic activity (Isaacson et al, 2002); Beta, B , and Delta, Del , gain of function in the lycopene β - and ε -cyclase ( CYC-b ; LCY-e ) genes (Gil et al, 1999; Ronen et al, 2000); high-pigment 3, hp3 , loss of function in the transcript coding for the zeaxanthin epoxydase ( ZEP ) (Galpaz et al, 2008); neoxanthin deficient 1, nxd1 , defected in the neoxathin synthase (NXS) enzymatic activity (Neuman et al, 2014). In this context, the only known exception of a carotenoid structural gene which, if mutated, does not affect the berry color is represented by the β -carotene hydroxylase 2 ( CHY2 ), whose knock out produce the, so called, white flower ( wf ) mutant, displaying, respectively, regular and not pigmented fruits and flowers (Galpaz et al, 2006).…”

Involvement of aerial organs on the ABA accumulation in roots of Citrus plants under water deficit

“…Moreover, the availability of the specific substrate 9-cis-neoxanthin and trans-violaxanthin (Fig. 5), which could turn into 9-cis-violaxanthin by action of a yet undiscovered 9-cis-isomerase (Nambara and Marion-Poll, 2005;Neuman et al, 2014), was not sufficient to ensure ABA accumulation.…”

“…1) could lead to an unspecific cleavage of these compounds and consequently, to a sharp reduction in their content. In this sense, it is believed that the neoxanthin synthase (NSY) function could be in fact exerted by a lycopene cyclase (LCY; Neuman et al 2014) and that carotenoid cleavage dioxygenases (CCDs) are able to metabolize most of the carotenoids present in plants meanwhile co-oxidation of carotenoids could be taking place by the action of free radicals generated by other stress-induced reactions (Fleischmann and Holger, 2008).…”

“…Zeaxanthin is then converted to violaxanthin by two successive epoxidation reactions via antheraxanthin by zeaxanthin epoxidase enzyme (ZEP; Chen and Gallie, 2012). Violaxanthin could be then converted into neoxanthin by means of the neoxanthin synthase (NSY; North et al, 2007;Neuman et al, 2014).…”