Cloning and characterization of two 9-cis-epoxycarotenoid dioxygenase genes, differentially regulated during fruit maturation and under stress conditions, from orange (Citrus sinensis L. Osbeck)

Abstract

There is now biochemical and genetic evidence that oxidative cleavage of cis-epoxycarotenoids by 9-cis-epoxycarotenoid dioxygenase (NCED) is the critical step in the regulation of abscisic acid (ABA) synthesis in higher plants. The peel of Citrus fruit accumulates large amounts of ABA during maturation. To understand the regulation of ABA biosynthesis in Citrus, two full-length cDNAs (CsNCED1 and CsNCED2) encoding NCEDs were isolated and characterized from the epicarp of orange fruits (Citrus sinensis L. Osbeck). Expression of the CsNCED1 gene increased in the epicarp during natural and ethylene-induced fruit maturation, and in water-stressed leaves, in a pattern consistent with the accumulation of ABA. The second gene, CsNCED2, was not detected in dehydrated leaves and, in fruits, exhibited a differential expression to that of CsNCED1. Taken together, these results suggests that CsNCED1 is likely to play a primary role in the biosynthesis of ABA in both leaves and fruits, while CsNCED2 appears to play a subsidiary role restricted to chromoplast-containing tissue. Furthermore, analysis of 9-cis-violaxanthin and 9'-cis-neoxanthin, as the two possible substrates for NCEDs, revealed that the former was the main carotenoid in the outer coloured part of the fruit peel as the fruit ripened or after ethylene treatment, whereas 9'-cis-neoxanthin was not detected or was in trace amounts. By contrast, turgid and dehydrated leaves contained 9'-cis-neoxanthin but 9-cis-violaxanthin was absent. Based on these results, it is suggested that 9-cis-violaxanthin may be the predominant substrate for NCED in the peel of Citrus fruits, whereas 9'-cis-neoxanthin would be the precursor of ABA in photosynthetic tissues.

Abscisic acid (ABA)-mediated inhibition of seed germination involves a positive feedback regulation of ABA biosynthesis in Arachis hypogaea L.

“…The NCED enzyme was first identified by analysis of the maize viviparous 14 (vp14) mutant Schwartz et al, 1997). NCED genes have subsequently been identified in several species, including tomato (Burbidge et al, 1997), bean (Qin and Zeevaart, 1999), cowpea (Iuchi et al, 2000), avocado (Chernys and Zeevaart, 2000), Arabidopsis (Iuchi et al, 2001), grape (Soar et al, 2004), orange (Rodrigo et al, 2006), potato (Destefano-Beltran et al, 2006), Stylosanthes guianensis (Yang and Guo, 2007), Gentiana lutea (Zhu et al, 2007), cleavers (Kraft et al, 2007), Cuscuta reflexa (a parasitic plant lacking neoxanthin) (Qin et al, 2008), Cistus creticus (a Mediterranean shrub) (Munne-Bosch et al, 2009), and persimmon (Leng et al, 2009). We characterized a dehydration-inducible NCED gene, AhNCED1 (GenBank accession no.…”

Control endógeno y exógeno de la maduración externa de los frutos cítricos

“…Los niveles de clorofila, bajo este punto de vista, estarían determinados por un balance entre su síntesis y su degradación y el cambio de color ocurriría como consecuencia del desplazamiento de dicho balance hacia la disminución de la síntesis de clorofila (Jacob-Wilk et al, 1999). Durante el proceso de desverdizado, la piel de los cítricos acumula grandes cantidades de carotenoides oxigenados responsables de la coloración (Eilati et al, 1969b;Goldschmidt et al, 1973;Molnár y Szabolcs, 1980;Gross, 1981;Rodrigo et al, 2003Rodrigo et al, , 2006. La concentración y composición de éstos varía considerablemente entre las distintas especies y cultivares y depende de las condiciones ambientales (Gross, 1977).…”

“…Durante la maduración, la piel de los frutos acumula carotenoides oxigenados (Molnár y Szabolcs, 1980;Rodrigo et al, 2003Rodrigo et al, , 2006 y ácido abscísico (Goldschmidt, 1976;Aung et al, 1991;Lafuente et al, 1997, Rodrigo et al, 2003, Agustí et al, 2007. Los epoxy-carotenoides, violaxantina y neoxantina, son precursores del ABA (Rock y Zeevaart, 1991).…”

“…Lo mismo ocurre con la expresión de los genes responsables de la codificación de las enzimas ACS y ACO (Nakatsuka et al, 1998). En frutos no-climatéricos como los cítricos, la aplicación de etileno también induce proteínas específicas de la maduración (Alonso et al, 1995;Rodrigo et al, 2006;Agustí, et al, 2007;Fujii et al, 2007) y aumento de la tasa respiratoria (Reid y Pratt, 1970).Los procesos anabólicos requeridos durante la maduración (síntesis de proteínas y ARNm, pigmentos y compuestos aromáticos) demandan energía y esqueletos carbonados, suministrados, al igual que en otros tejidos, por la respiración. La tasa de consumo de azúcares y ácidos está supeditada, en gran medida, a la actividad respiratoria del fruto, la cual depende fundamentalmente de la especie y la temperatura (Sozzi, 2007).…”

“…Lo mismo ocurre con la expresión de los genes responsables de la codificación de las enzimas ACS y ACO (Nakatsuka et al, 1998). En frutos no-climatéricos como los cítricos, la aplicación de etileno también induce proteínas específicas de la maduración (Alonso et al, 1995;Rodrigo et al, 2006;Agustí, et al, 2007;Fujii et al, 2007) y aumento de la tasa respiratoria (Reid y Pratt, 1970).…”