Genetic control of seed proteins by a spontaneous defective kernel mutant of maize

A spontaneous mutation which conditions defective kernels was found in the WK-01 red flint line. The mutation conditions kernels of small size, their approximate weight being 27% of the normal kernels of the same ear.

The characteristic of these kernels is that they present a floury endosperm, a reduced embryo and endosperm, a pale yellow color and the pericarp separated in some parts from the aleuroniferous layer. The progeny of normal kernels, heterozygous for the mutation, is characterized by the segregation of normal kernels and defective kernels in a ratio 3:1, respectively. The results obtained in the analysis of 5 F2 ears (see Table 1) allow us to infer that the character of the defective kernel is controlled by a single recessive gene, which is referred to as de*-7601. The kernels that have the gene de*-7601 have an average weight of 72.0 mg, whereas the normal ones have an average weight of 267.5 mg. In the normal kernels the endosperm represents 85.6% of the complete kernel's weight, while in the defective ones only 77.8%. The germ represents 10.8% of the normal kernel's weight but in the defective ones 9.9%. These results show that both the endosperm and the germ are affected by the mutation, reducing their proportions in the defective kernel.

The gene de*-7601 is lethal, because although 50% of the defective kernels germinate, the seedlings die in different developmental stages.

The purpose of this work is to determine the effect of gene de*-7601 over the kernel proteins. For this reason a comparative analysis was performed between the defective kernels and their normal equivalents, which have the same genetic background.

The storage proteins of the endosperm were fractionated according to Landry-Moureaux (1970), and the results are shown in Table 2. The protein pattern of the defective kernels notably differs from that of the normal kernels and is characterized by a lower proportion of zein and a higher proportion of albumins, globulins and glutelin-3.

The mutant de*-7601 acts as other known regulatory genes which repress the synthesis of zein and conditions a higher proportion of albumins, globulins and glutelin-3. These modifications consequently bring about an increase in the lysine level (see Table 2). In order to establish whether there are any differences in the molecular composition of the greatest storage protein, the zein, this was fractionated by means of electrophoresis in polyacrylamide gel. The polypeptide pattern of zein in de*-7601 is similar to that of normal kernels, but the fifth (zp5) polypeptide is completely repressed as it does not appear (see Figure 1). Comparing the soluble proteins of the endosperm separated in polyacrylamide gel, two components are also absent in the polypeptide pattern of de*-7601 (see Figure 2).

It was also considered interesting to study the polypeptide patterns of the germ proteins. In Figure 3, the patterns of the soluble proteins of the germ, which are the ones that are found in a higher proportion, are compared. In this case the kernels which carry de*-7601 do not synthesize, in the germ, three polypeptides which are found in normal germs.

In the germ, the molecular patterns of the lipoproteins were also analyzed, these being a group of proteins characteristic in the maize germ, because in the endosperm they are found in low proportion. In Figure 4 it can be seen that, contrary to what occurred in the previous cases, where the molecular patterns of the defective kernel proteins showed the lack of some polypeptides, three new polypeptides are synthesized in the lipoproteins of the germs that have the gene de*-7601.

Several modifications occurred in the defective kernels, the most evident of which is the great reduction in the size of the kernel. In this particular case the normal development both of the endosperm and the germ is blocked, as a result of which the seed loses its viability or at least is incapable of originating a normal plant, as these die early in their development.

Apart from the modifications caused by the mutants which condition defective kernels, there are the modifications that are presented in this paper and which are exercised on the kernel proteins.

The results obtained allow us to infer in the first place that at least for this particular case, the locus de*-7601 is a regulatory gene which controls the synthesis of the endosperm proteins, deeply altering the normal protein pattern. Nevertheless, there also exist differences as regards the level of structural genes in the polypeptide patterns. In general, the blockage in the synthesis of some of the polypeptides which are perhaps essential enzymes for the normal development and viability of the kernel, leads us to suppose that there is a strong probability that the mutation of the defective kernel affects several strongly linked genes, at least one of which is a regulatory element and several of which have structural functions.

Table 1.

Table 2.

Figures 1-4.

Jorge Luis Magoja


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