The maize regulatory locus Opaque-2 encodes a DNA-binding protein which activates the transcription of the b-32 gene.

Lohmer, Stefan; Maddaloni, Massimo; Motto, M.; Fonzo, N. di; Hartings, H.; Salamini, F.; Thompson, Richard

doi:10.1002/j.1460-2075.1991.tb07989.x

Cited by 219 publications

(223 citation statements)

References 54 publications

(82 reference statements)

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“…7) of enzyme extracted from normal and opaque-2 endosperms suggested that the opaque-2 mutation may affect the synthesis of LKR rather than its structure. The recent cloning of the Opaque-2 gene has demonstrated that Opaque-2 codes for a DNA binding protein that transactivates the 22 kD zein and b-32 genes (14,17,21,22). It is possible that the same transacting factor is involved in the expression of the LKR gene.…”

Section: Discussionmentioning

confidence: 99%

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Partial Purification and Characterization of Lysine-Ketoglutarate Reductase in Normal and Opaque-2 Maize Endosperms

Brochetto-Braga¹,

Leite²,

Arruda³

1992

Plant Physiol.

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Lysine-ketoglutarate reductase catalyzes the first step of lysine catabolism in maize (Zea mays L.) endosperm. The enzyme condenses L-lysine and a-ketoglutarate into saccharopine using NADPH as cofactor. It is endosperm-specific and has a temporal pattern of activity, increasing with the onset of kernel development, reaching a peak 20 to 25 days after pollination, and thereafter decreasing as the kernel approaches maturity. The enzyme was extracted from the developing maize endosperm and partially purified by ammonium-sulfate precipitation, anion-exchange chromatography on DEAE-cellulose, and affinity chromatography on Blue-Sepharose CL-6B. The preparation obtained from affinity chromatography was enriched 275-fold and had a specific activity of 411 by the opaque-2 mutation may explain, at least in part, the elevated concentration of lysine found in the opaque-2 endosperm.There is little information on lysine catabolism in higher plants. Most of the available data were obtained in studies on the incorporation and metabolism of radiolabeled precursors by plant tissues. Feeding experiments with ["4C]lysine demonstrated the incorporation of radioactivity into a-amino adipic acid and glutamic acid in wheat (18) and into saccharopine and diaminopimelic acid in maize and barley (16,26). In developing endosperm of maize and barley, radiolabeled lysine is incorporated primarily into glutamic acid and proline (4, 26). These findings indicate that lysine is catabolized in plants via the saccharopine pathway.The first enzymatic evidence for the operation of the saccharopine pathway for lysine catabolism in plants was obtained with the demonstration of LKR3 activity in immature endosperm of maize (3). LKR (EC 1.5.1.8) condenses lysine and a-ketoglutarate into saccharopine using NADPH as cofactor.An understanding of the pathways for lysine biosynthesis and degradation in plants has enormous importance because of the limiting concentration of this essential amino acid in major food sources such as cereals. Valuable information can be obtained by the elucidation of the properties of enzymes involved in the biosynthesis and catabolism of lysine and by the use of mutants in which the activities of the enzymes are altered.Since the discovery of the superior nutritive value of the high lysine maize mutant opaque-2 (15), there have been many studies on the effects of this mutant gene on protein and amino acid metabolism in maize endosperm. The opaque-2 gene is located on the short arm of chromosome 7 and its major effect is the reduction of the maize storage protein zein. This is a complex of polypeptides coded by a multigenic family located on chromosomes 4 and 7 (23). The opaque-2 gene in the homozygous form reduces the zein content of the endosperm by up to 70% (6). The reduction is

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Section: Discussionmentioning

confidence: 99%

“…The opaque-2 endosperm lacks an albumin of 32 kD (b-32) with unknown function whose accumulation pattern is coordinated with zein accumulation in normal endosperms (24). The gene encoding b-32 is transactivated by the opaque-2 gene product (14). The opaque-2 mutation also affects lysine catabolism.…”

mentioning

confidence: 99%

Partial Purification and Characterization of Lysine-Ketoglutarate Reductase in Normal and Opaque-2 Maize Endosperms

Brochetto-Braga¹,

Leite²,

Arruda³

1992

Plant Physiol.

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“…Circumstantial evidence has been in this sense obtained by nutrient manipulation in field studies ( l s a i eta/., 1978), long-term kernel cultures (Singletary and Below, 1989;Singletary et al, 1990), and endosperm cell cultures (Balconi et a/., 1991;Lyznick and Tsai, 1989).…”

Section: Introductionmentioning

confidence: 99%

The accumulation of zein polypeptides and zein mRNA in cultured endosperms of maize is modulated by nitrogen supply

et al. 1993

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SummaryThe effect of nitrogen (N) nutrition upon the accumulation of seed storage protein has been studied in wildtype and opaqoe-2 mutant (02) maize endosperms grown in vitro, for 5 days, on a solid medium containing different amounts of N in the form of inorganic or organic compounds. As reference, the accumulation of zein proteins in endosperms grown to maturity in vivo under field conditions was also examined. The developmental stage up to 14-19 days after pollination (DAP) defines, both in vivo and in vitro, a phase of growth during which the major zein classes of 20 and 22 kDa are synthesized both in wild-type and o2endo-sperms. In vitro, the corresponding transcripts of the genes coding the 20 and 22 kDa zeins, and of the zein synthesis associated gene b-32, are also present. Under in vitro conditions, the level of expression of the zein synthesizing system, as monitored by zein accumulation, is dependent on the level and form of N supplied in the medium. In vivo, at stages of development from 19 DAP to maturity, the synthesis of the 22 kDa zein class and of the b-32 protein is under control of the 02 transcriptional activator. It is hypothesized that at early stages of endosperm development (between 9 and 14-19 DAP) a 'metabolic control', based on N availability, is operative, possibly based on a regulatory factor different from 02.

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“…This integration may occur through interactions with other transcription factors and through binding to multiple regulatory motifs within promoters. The Opaque-2 protein contains leucine zipper domains (Schmidt et al, 1990 ;Lohmer et al, 1991), suggesting that it is involved in interactions with other proteins, probably other transcription factors. The amino acid sequence of the Opaque-2 DNA-binding domain is similar to the region of the Em-binding protein (a well characterized ABA-related transcription factor ; Guiltinan, Marcotte & Quatrano, 1990) that binds ABAresponsive promoter elements.…”

Section: Transcriptional Regulationmentioning

confidence: 99%

“…The amino acid sequence of the Opaque-2 DNA-binding domain is similar to the region of the Em-binding protein (a well characterized ABA-related transcription factor ; Guiltinan, Marcotte & Quatrano, 1990) that binds ABAresponsive promoter elements. The Opaque-2 binding domain also has homology to the DNA-binding domain of a transcription factor that binds to the TGACGT motif (also part of an O2S element) in histone gene promoters (Schmidt et al, 1990 ;Lohmer et al, 1991 ;Lanahan et al, 1992). The O2S motif is found in ABA-regulated genes such as RAB (Mundy, Yamaguchi-Shinozaki & Chua, 1990) and Opaque-2 has been shown to regulate the expression of seed storage proteins during maturation (Lohmer et al, 1991).…”

Section: Transcriptional Regulationmentioning

confidence: 99%

Gibberellins: regulating genes and germination

Ritchie

Gilroy

1998

New Phytologist

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The range of processes regulated by gibberellins (GAs) covers all aspects of the life history of the plant from seed germination to vegetative growth and flowering. In seeds there has been an intensive search, using the techniques of both biochemistry and cell biology, for the regulatory molecules linking GA perception to gene regulation and the events of germination. Although a GA receptor has yet to be identified, the site of perception has been localized to the plasma membrane. Calmodulin, Ca2+ and cGMP have also been identified as elements of the GA signal transduction pathway. These regulators parallel many of the signalling elements identified in the transduction of other signals such as phytochrome and ABA. Studies of GA‐regulated gene expression, principally of the α‐amylases of cereal aleurone, have identified core GA‐responsive promoter elements, such as the gibberellin response element (GARE), box‐1 and pyrimidine boxes, as well as elements that may lend specificity to GA‐regulated expression, such as the Opaque‐2‐similar element (O2S), and TRE and CRE motifs. One of the most striking features of all of these studies of the molecular basis of GA action is the interaction of GA‐dependent regulatory elements with those of other factors such as ABA. GA‐response elements also appear to be conserved between disparate GA‐response systems. For example, Myb transcription factors appear to regulate a multitude of GA‐induced genes in cereal aleurone as well as to alter GA responses when expressed in Arabidopsis. Thus the study of GA signal transduction and response systems is highlighting the conservation of regulatory elements used by plants. These common factors, used by distinct signal transduction systems, provide a molecular basis for the integration of the GA signal with other growth regulators that is the hallmark of plant growth and development.

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The maize regulatory locus Opaque-2 encodes a DNA-binding protein which activates the transcription of the b-32 gene.

Cited by 219 publications

References 54 publications

Partial Purification and Characterization of Lysine-Ketoglutarate Reductase in Normal and Opaque-2 Maize Endosperms

Partial Purification and Characterization of Lysine-Ketoglutarate Reductase in Normal and Opaque-2 Maize Endosperms

The accumulation of zein polypeptides and zein mRNA in cultured endosperms of maize is modulated by nitrogen supply

Gibberellins: regulating genes and germination

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