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 brown-midrib mutants of maize have a reddish-brown pigmentation of the leaf midrib and stalk pith, associated with lignified tissues. These mutants progressively became models for lignification genetics and biochemical studies in maize and grasses. Comparisons at silage maturity of bm1, bm2, bm3, bm4 plants highlighted their reduced lignin, but also illustrated the biochemical specificities of each mutant in p-coumarate, ferulate ester and etherified ferulate content, or syringyl/guaiacyl monomer ratio after thioacidolysis. Based on the current knowledge of the lignin pathway, and based on presently developed data and discussions, C3H and CCoAOMT activities are probably major hubs in controlling cell-wall lignification (and digestibility). It is also likely that ferulates arise via the CCoAOMT pathway.

Improving digestibility is a major goal for forage maize (Zea mays L.) breeding programs. Quantitative trait loci (QTL) affecting forage maize digestibility‐related and agronomic traits were mapped and characterized in a set of recombinant inbred lines (RIL). Eleven traits were analyzed on whole plant samples: neutral detergent fiber (NDF), starch content (STC), crude protein content (CPC), acid detergent lignin (ADL), in vitro dry matter digestibility (IVDMD), in vitro cell wall digestibility (IVNDFD), in vitro digestibility of non‐starch and non‐soluble carbohydrate (IVDNSC), dry matter content (DMC), dry matter yield (DMY), mid‐silk date (SILK), and plant height (PHT). Evaluation was performed among the RIL populations studied per se (RILps) and in combination with a tester (TC). The genetic variances (σ2g) were highly significant and, in most cases, greater than genotype × year interaction variances (σ2g×y). Heritabilities ranged from 0.49 to 0.70 in RILps and from 0.12 to 0.58 in TC. Twenty‐eight QTL were identified among TC by CIM, which explained individually between 3.3 and 20.2% of the phenotypic variation (R2p) for traits related to digestibility or agronomic performance. Twenty QTL were identified among RILps, which explained individually between 6.5 and 15.3% of the phenotypic variation (R2p). Seven of these QTL were common to TC and RILps. Cell wall digestibility estimates (IVNDFD or IVDNSC) were the traits with the highest number of QTL. In contrast, we detected only one QTL for dry matter digestibility (IVDMD). Thus, it may be useful to separate IVDMD into its two component parts, cell wall digestibility, which could be estimated from line per se values, and starch content. Characteristics such as IVDNSC or IVNDFD, coupled with QTL information, would be powerful tools in the search for genes involved in maize lignification or cell wall biogenesis.

We describe a procedure allowing extraction of total proteins that performs efficiently with a large variety of plant tissues, based on simultaneous precipitation and denaturation with TCA and 2ME in cold acetone. We also describe protein solubilization prior to IEF, either in classical rod gels or in IPGs, using two different solutions. The procedure is easy to carry out. The major caveats are (1) keep samples at low temperature during extraction, and then (2) manage protein samples at about 22 to 25 degrees C to avoid urea precipitation.