Although the morphological steps of maize (Zea mays) endosperm development are well described, very little is known concerning the coordinated accumulation of the numerous proteins involved. Here, we present a proteomic study of maize endosperm development. The accumulation pattern of 409 proteins at seven developmental stages was examined. Hierarchical clustering analysis allowed four main developmental profiles to be recognized. Comprehensive investigation of the functions associated with clusters resulted in a consistent picture of the developmental coordination of cellular processes. Early stages, devoted to cellularization, cell division, and cell wall deposition, corresponded to maximal expression of actin, tubulins, and cell organization proteins, of respiration metabolism (glycolysis and tricarboxylic acid cycle), and of protection against reactive oxygen species. An important protein turnover, which is likely associated with the switch from growth and differentiation to storage, was also suggested from the high amount of proteases. A relative increase of abundance of the glycolytic enzymes compared to tricarboxylic acid enzymes is consistent with the recent demonstration of anoxic conditions during starch accumulation in the endosperm. The specific late-stage accumulation of the pyruvate orthophosphate dikinase may suggest a critical role of this enzyme in the starch-protein balance through inorganic pyrophosphate-dependent restriction of ADP-glucose synthesis in addition to its usually reported influence on the alanine-aromatic amino acid synthesis balance.

The capacity of two maize opaque endosperm mutants (o1 and o2) and two floury (fl1 and fl2) to accumulate lysine in the seed in relation to their wild type counterparts Oh43+ was examined. The highest total lysine content was 3.78% in the o2 mutant and the lowest 1.87% in fl1, as compared with the wild type (1.49%). For soluble lysine, o2 exhibited over a 700% increase, whilst for fl3 a 28% decrease was encountered, as compared with the wild type. In order to understand the mechanisms causing these large variations in both total and soluble lysine content, a quantitative and qualitative study of the N constituents of the endosperm has been carried out and data obtained for the total protein, nonprotein N, soluble amino acids, albumins/globulins, zeins and glutelins present in the seed of the mutants. Following two-dimensional PAGE separation, a total of 35 different forms of zein polypeptides were detected and considerable differences were noted between the five different lines. In addition, two enzymes of the aspartate biosynthetic pathway, aspartate kinase and homoserine dehydrogenase were analyzed with respect to feedback inhibition by lysine and threonine. The activities of the enzymes lysine 2-oxoglutate reductase and saccharopine dehydrogenase, both involved in lysine degradation in the maize endosperm were also determined and shown to be reduced several fold with the introduction of the o2, fl1 and fl2 mutations in the Oh43+ inbred line, whereas wild-type activity levels were verified in the Oh43o1 mutant.

Monosymmetry evolved several times independently during flower evolution. In snapdragon (Antirrhinum majus), a key gene for monosymmetry is CYCLOIDEA (CYC), which belongs to the class II TCP gene family encoding transcriptional activators. We address the questions of the evolutionary history of this gene family and of possible recruitment of genes homologous to CYC in floral development and symmetry in the Papaveraceae. Two to three members of the class II TCP family were found in each species analyzed, two of which were CYC-like genes, on the basis of the presence of both the TCP and R conserved domains. The duplication that gave rise to these two paralogous lineages (named PAPACYL1 and PAPACYL2) probably predates the divergence of the two main clades within the Papaveraceae. Phylogenetic relationships among angiosperm class II TCP genes indicated that (1) PAPACYL genes were closest to Arabidopsis (Arabidopsis thaliana) AtTCP18, and a duplication at the base of the core eudicot would have given rise to two supplementary CYC-like lineages; and (2) at least three class II TCP genes were present in the ancestor of monocots and eudicots. Semiquantitative reverse transcription-polymerase chain reaction and in situ hybridization approaches in three species with different floral symmetry indicated that both PAPACYL paralogs were expressed during floral development. A pattern common to all three species was observed at organ junctions in inflorescences and flowers. Expression in the outer petals was specifically observed in the two species with nonactinomorphic flowers. Hypotheses concerning the ancestral pattern of expression and function of CYC-like genes and their possible role in floral development of Papaveraceae species leading to bisymmetric buds are discussed.