Temporal profiling of essential amino acids in developing maize kernel of normal, opaque-2 and QPM germplasm

Abstract

Maize, an important cereal crop, has a poor quality of endosperm protein due to the deficiency of essential amino acids, especially lysine and tryptophan. Discovery of mutants such as opaque-2 led to the development of nutritionally improved maize with a higher concentration of lysine and tryptophan. However, the pleiotropic effects associated with opaque-2 mutants necessitated the development of nutritionally improved hard kernel genotype, the present-day quality protein maize (QPM). The aim of present study was to analyze and compare the temporal profile of lysine and tryptophan in the developing maize kernel of normal, opaque-2 and QPM lines. A declining trend in protein along with tryptophan and lysine content was observed with increasing kernel maturity in the experimental genotypes. However, opaque-2 retained the maximum concentration of lysine (3.43) and tryptophan (1.09) at maturity as compared to QPM (lysine-3.05, tryptophan-0.99) and normal (lysine-1.99, tryptophan-0.45) lines. Opaque-2 mutation affects protein quality but has no effect on protein quantity. All maize types are nutritionally rich at early stages of kernel development indicating that early harvest for cattle feed would ensure a higher intake of lysine and tryptophan. Two promising lines (CML44 and HKI 1105) can be used for breeding high value corn for cattle feed or human food in order to fill the protein inadequacy gap. Variation in lysine and tryptophan content within QPM lines revealed that differential expression of endosperm modifiers with varying genetic background significantly affects nutritional quality, indicating that identification of alleles affecting amino acid composition can further facilitate QPM breeding program.

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

“…All the fractions were subsequently processed for nitrogen estimation to obtain protein content by micro-Kjeldahl method (AOAC 1975). The protein concentration of the above-mentioned fractions was estimated by considering the total protein percentage as 100% and the total protein content of each accession was reported earlier 24 .…”

“…Due to their high levels of expression and complexity, zein synthesis serves as a model system to analyze coordinated genetic regulation of several genes expressed at at a specific developmental stage 21 . Although a lot of information regarding the molecular mechanism of nutritionally improved maize is available [22][23][24] , differential expression of protein fractions under different genetic backgrounds with respect to endosperm development is not well understood. The expression profile of endosperm modifiers in QPM at different levels of kernel maturity was also not well understood in maize.…”

Elucidation of zein isoforms associated with high protein quality traits for targeted improvement in maize‐based nutrition

“…The total protein content among normal, opaque‐2 , and QPM lines was 14.05%, 13.43%, and 12.42%, respectively (Sethi, Kumar, et al, 2020). Zein content was the highest in normal lines (51.31%), intermediate in QPM (28.08%), and the lowest in opaque‐2 (19.5%), whereas nonzein content was the highest in opaque‐2 (75.73%), intermediate in QPM (70.35%), and the lowest in normal lines (45.11%).…”

“…Retention of less moisture content by QPM lines will lead to tolerance to stored grain insect pests. Also, three lines, including normal (HKI‐1105N), opaque‐2 (DQI‐1001), and QPM (HKI‐1105) showing maximum variability for protein quality were selected for 2D‐PAGE analysis (Sethi et al, 2020, 2021). Before 2D‐PAGE analysis, the total zeins isolated were separated by SDS‐PAGE.…”

“…Concomitantly, biochemical parameters including total protein, zein content, nonzein content, and prolamin‐like content were also recorded for 2 years in three replicates. The procedure for all the physiological and biochemical parameters mentioned above was followed according to previous studies (Sethi, Kaur, et al, 2020; Sethi, Kumar, et al, 2020).…”