The Arabidopsis cytochrome P450 CYP707A encodes ABA 8′-hydroxylases: key enzymes in ABA catabolism

Abstract

The hormonal action of abscisic acid (ABA) in plants is controlled by the precise balance between its biosynthesis and catabolism. In plants, ABA 8 0 -hydroxylation is thought to play a predominant role in ABA catabolism. ABA 8 0 -hydroxylase was shown to be a cytochrome P450 (P450); however, its corresponding gene had not been identified. Through phylogenetic and DNA microarray analyses during seed imbibition, the candidate genes for this enzyme were narrowed down from 272 Arabidopsis P450 genes. These candidate genes were functionally expressed in yeast to reveal that members of the CYP707A family, CYP707A1-CYP707A4, encode ABA 8 0 -hydroxylases. Expression analyses revealed that CYP707A2 is responsible for the rapid decrease in ABA level during seed imbibition. During drought stress conditions, all CYP707A genes were upregulated, and upon rehydration a significant increase in mRNA level was observed. Consistent with the expression analyses, cyp707a2 mutants exhibited hyperdormancy in seeds and accumulated six-fold greater ABA content than wild type. These results demonstrate that CYP707A family genes play a major regulatory role in controlling the level of ABA in plants.

Abscisic acid levels in tomato ovaries are regulated by LeNCED1 and SlCYP707A1

“…However, no diVerences were found between 7Ј-hydroxy ABA and neo-PA levels in ovaries after pollination, suggesting that these conversions take place, but do not attribute to the decrease in ABA levels after pollination. Thus, ABA 8Ј-hydroxylation is the major ABA catabolic pathway in tomato ovaries (our work) as was suggested for Arabidopsis (Kushiro et al 2004). ABA can be transported and stored as ABA-GE (Nambara and Marion-Poll 2005) and the high levels in unpollinated ovaries could mean that ABA-GE is transported to and stored in the ovary.…”

“…The localization of SlCYP707A1 mRNA is comparable to the localization of the hormone ABA in the ovules of Arabidopsis and cucumber (Peng et al 2006). The decrease in mRNA levels of the three other putative tomato CYP707A genes might be explained by the reduction in ABA concentration, since positive feedback from ABA on CYP707A expression has been found in Arabidopsis (Kushiro et al 2004;Umezawa et al 2006), potato (Destefano-Beltran et al 2006) and by us in tomato (Fig. 6b).…”

“…In plant cells, ABA is mainly inactivated by 8Ј-hydroxylation (Nambara and Marion-Poll 2005), which is in Arabidopsis catalyzed by four cytochrome P450 mono-oxygenases, AtCYP707A1 to AtCYP707A4 (Kushiro et al 2004). We previously identiWed a tomato homolog of AtCYP707A4, which was strongly induced in the ovary after pollination (Vriezen et al 2008).…”

“…The deduced amino acid sequence is highly homologous to the Arabidopsis CYP707A4 protein (65% amino acid identity) and Solanum tuberosum CYP707A2 gene (95% identity). The tomato protein (designated SlCYP707A1) contains the highly conserved cysteine residue (within the PFGNGTHSCPG motif), which is the putative heme-ironligand, common to all P450s and essential for catalytic activity (Kushiro et al 2004). A database search yielded three more putative CYP707A ESTs (TC177455, AI484420, and TC186477) that share between 61 and 68% sequence identity with SlCYP707A1 at nucleotide level.…”

“…Transcription levels of a gene very homologous to an Arabidopsis ABA 8Ј-hydroxylase (AtCYP707A4) were strongly induced speciWcally in ovules and placenta tissue, in contrast to the mRNA levels of the three other putative tomato CYP707A genes. Similarly, the CYP707A genes in Arabidopsis are also diVerentially expressed, for instance during dehydration and rehydration responses and during seed dormancy (Kushiro et al 2004;Okamoto et al 2006). The deduced protein sequence of SlCYP707A1 has very high homology to AtCYP707A4.…”