Expression profile of protein fractions in the developing kernel of normal, Opaque-2 and quality protein maize

Abstract

Maize protein quality is determined by the composition of its endosperm proteins, which are classified as nutritionally poor zeins (prolamin and prolamin-like) and nutritionally rich non-zeins (albumin, globulin, glutelin-like, and glutelin). Protein quality is considerably higher in opaque-2 mutants due to increased content of non-zeins over zeins. However, the opaque-2 endosperm is soft, which leads to poor agronomic performance and post-harvest infestation. Endosperm modification of opaque-2 had led to the development of Quality Protein Maize (QPM), which has higher protein quality along with hard kernel endosperm. The present study was planned to analyze the expression dynamics of different protein fractions in the endospem of developing maize kernel in normal, opaque-2 and QPM in response to the introgression of endosperm modifiers. Results revealed that albumin and globulin content decreases, whereas, prolamin, prolamin-like, glutelin-like, and glutelin content increases with kernel maturity. It has been observed that opaque-2 mutation affects protein expression at initial stages, whereas, the effect of endosperm modifiers was observed at the intermediate and later stages of kernel development. It has also been noted that prolamin, glutelin, and glutelin-like fractions can be used as quick markers for quality assessment for differentiating QPM varieties, even at the immature stage of kernel development. Overall, the present study implicates the role of different protein fractions in developing and utilizing nutritionally improved maize varieties.

Figure 1

Trends of endosperm protein fractions accumulation at different stages of kernel development (Mean ± S.D.). Protein fractions are estimated by considering total protein percentage as 100% and total protein content is estimated on dry weight-basis. The small alphabets on top of the bar represent the significance level, as per critical difference. Identical alphabet represents non-significant variation at P < 0.05.

Figure 2

Comparison of protein fractions including zein (A, B) and non-zein (C, D, E, F) between normal, opaque-2 and QPM lines at different stages of kernel development. Error bars denote ± SD of three replicates. The small alphabets on top of the bar represent the significance level, as per critical difference. Identical alphabet represents non-significant variation at P < 0.05.

Figure 3

Dendrogram of normal (1–16), opaque-2 (17–23), QPM (24–30) lines based on prolamin (A), prolamine-like (B), albumin (C), globulin (D), glutelin-like (E) and glutelin fractions (F). Dendrogram analysis on group average, squared euclidean basis. For numbering of normal, opaque-2 and QPM genotypes, refer Supplementary Table 1.