Characterization of monofunctional aspartate kinase genes in maize and their relationship with free amino acid content in the endosperm

Abstract

A quantitative trait locus has previously been identified in maize (Zea mays L.) that influences the level of free amino acids in the endosperm, especially those from the aspartate pathway: lysine, threonine, methionine, leucine, and isoleucine. Because this locus occurs in a region of the genome containing ask2, a monofunctional aspartate kinase, the nature of the monofunctional aspartate kinase genes in the parental inbreds, Oh545o2 and Oh51Ao2, was investigated. Two genes, Ask1 and Ask2 were isolated, and Ask2 was mapped to the ask2 locus. Nucleotide sequence analysis of the Ask2 alleles from Oh545o2 and Oh51Ao2 showed they differ by one amino acid. Both alleles complemented a yeast aspartate kinase mutant, hom3, and based on the growth of the yeast mutant it appeared that Ask2-Oh545o2 produces an enzyme with greater total activity than that encoded by the Oh51Ao2 allele. The results suggest that the higher level of free amino acids derived from the aspartate pathway in Oh545o2 endosperm results from a single amino acid change in the ASK2 enzyme that has pleiotropic effects on its activity.

Inducible NAD overproduction in Arabidopsis alters metabolic pools and gene expression correlated with increased salicylate content and resistance to Pst‐AvrRpm1

“…In fact, stimulating Thr production in plants results in a simultaneous increase of the Ile pool (Gakière et al. , 2000; Wang et al. , 2007).…”

“…Second, higher levels of NAD(H) and NADP(H), which act as co-factors of bifunctional Aspartate Kinase-Homoserine Dehydrogenases, may have stimulated the synthesis of homoserine and its derivatives Met, Thr and Ile. In fact, stimulating Thr production in plants results in a simultaneous increase of the Ile pool (Gakiè re et al, 2000;Wang et al, 2007). The Met that was overproduced may be catabolised and this represents the source of Ile accumulation (Ravanel et al, 1998;Ré beillé et al, 2006).…”

The genetic architecture of amino acids dissection by association and linkage analysis in maize

“…Studies of the model plant Arabidopsis thaliana have focused on the roles of amino acids in nitrogen nutrition (Crawford and Forde, ), N‐assimilation (Coruzzi, ), metabolism and regulation (Hell and Wirtz, ; Ingle, ; Jander and Joshi, ; Tzin and Galili, ; Verslues and Sharma, ). Some key genes regulating free amino acid content have been identified in Arabidopsis (Angelovici et al ., ), tobacco (Maloney et al ., ), soya bean (Ishimoto et al ., ; Takahashi et al ., ), rapeseed (Moulin et al ., , ), rice (Kang et al ., ; Zhou et al ., ) and maize (Mertz et al ., ; Muehlbauer et al ., ; Shaver et al ., ; Wang et al ., , ). Opaque2 (O2) is an endosperm‐specific transcription factor belonging to the bZIP family, whose mutation could increase free lysine levels and enhance the overall nutritional value of grain by reducing the 22‐kD α‐ and β‐zein transcripts and proteins in maize (Hunter et al ., ; Kodrzycki et al ., ; Mertz et al ., ).…”

Nutritional Quality of Sorghum Seeds: Storage Proteins and Amino Acids

“…Cereal grains generally contain low levels of lysine , while legumes are normally deficient in methionine . Due to nutritional importance of these amino acids, the aspartate pathway has received special attention since the early 1970s, and a considerable amount of information has been obtained about the metabolic control of these amino acids (Gaziola et al, 1997;Arruda et al, 2000;Fornazier et al, 2005;Ferreira et al, 2006;Hudson et al, 2006;Nikiforova et al, 2006;Stepansky et al, 2006;Wang et al, 2007).…”