Genetic enhancement of essential amino acids for nutritional enrichment of maize protein quality through marker assisted selection

Dissecting the genetic architecture of polygenic nutritional traits in maize through meta-QTL analysis

Maize, as a staple crop, contributes significantly to global nutritional security. However, improving its nutritional quality, including grain zinc (GZn), grain iron (GFe), kernel oil (KO), protein quality (PQ), and content (PC), is difficult due to the complex and polygenic nature of these traits. In traditional quantitative trait loci (QTLs) mapping, different populations tested across variable environments have resulted in heterogeneous findings, highlighting the challenge of QTL instability. Therefore, we tested whether Meta-QTL (MQTL) analysis enables the identification of stable QTLs with broader allelic coverage and higher mapping resolution for effective marker-assisted selection (MAS) of complex traits. A comprehensive literature search revealed 29 mapping studies encompassing 308 QTLs for the targeted traits. A total of 34 stable MQTLs were identified, with an average CI of 4.59 cM. These MQTLs were located on all ten maize chromosomes, with phenotypic variance explained (PVE %) ranging from 7.3 % (MQTL1_2) to 49.0 % (MQTL3_2). Furthermore, the analysis revealed six MAS-friendly and five hotspot MQTLs. Besides, 591 CGs were identified underlying these MQTLs, of which 14 have known roles in grain filling, metal homeostasis, and fatty acid biosynthesis in maize. In silico analysis confirmed the tissue-specific expression of these 14 CGs. MQTL analysis effectively refined the genomic regions (4.86 folds) linked with nutritional quality and identified stable MQTLs and CGs. These findings will be useful for developing nutritionally enriched varieties through MAS and genetic engineering.

Maize kernel nutritional quality-an old challenge for modern breeders

MAIN CONCLUSION

This article offers a comprehensive overview of the starch, protein, oil, and carotenoids content in maize kernels, while also outlining future directions for research in this area. Maize is one of the most important cereal crops globally. Maize kernels serve as a vital source of feed and food, and their nutritional quality directly impacts the dietary intake of both animals and humans. Maize kernels contain starch, protein, oil, carotenoids, and a variety of vitamins and minerals, all of which are important for maintaining life and promoting health. This review presents the current understanding of the content of starch, protein, amino acids, oil, and carotenoids in maize kernels, while also highlighting knowledge gaps that need to be addressed.

Determinants of adoption of quality protein maize varieties in Misrak Badewacho District, Southern Ethiopia: policy implications

This study aimed to identify the determinants of adoption of quality protein maize (QPM) varieties. QPM varieties are promoted as a solution to the problem of undernutrition, and their adoption is especially important in areas where maize is a nutritional staple food source. This study employed a cross-sectional design. A multistage sampling procedure was used to collect primary data from 143 sampled maize producers, which were analyzed using SPSS version 22. A binary logit model was used to identify major determinants. The results indicated that access to QPM seed, land size, on-farm income, involvement in off/non-farm activities, frequency of contact with development agents (Das), educational level of the household head, and participation of farmers on field days were statistically significant determinants of QPM variety adoption. Credit use was also a significant determinant of the adoption of QPM varieties but showed a negative influence. Therefore, this study recommends that all relevant stakeholders working at different levels in QPM production and extension pay attention to the factors that could affect farmers' decisions to adopt QPM in the study area. Furthermore, all concerned bodies should work together to enhance the adoption of QPM varieties.

Molecular basis of one-step methyl anthranilate biosynthesis in grapes, sweet orange, and maize

Plants synthesize an array of volatile compounds, many of which serve ecological roles in attracting pollinators, deterring herbivores, and communicating with their surroundings. Methyl anthranilate (MeAA) is an anti-herbivory defensive volatile responsible for grape aroma that is emitted by several agriculturally relevant plants, including citrus, grapes, and maize. Unlike maize, which uses a one-step anthranilate methyltransferase (AAMT), grapes have been thought to use a two-step pathway for MeAA biosynthesis. By mining available transcriptomics data, we identified two AAMTs in Vitis vinifera (wine grape), as well as one ortholog in "Concord" grape. Many angiosperms methylate the plant hormone salicylic acid (SA) to produce methyl salicylate, which acts as a plant-to-plant communication molecule. Because the Citrus sinensis (sweet orange) SA methyltransferase can methylate both anthranilate (AA) and SA, we used this enzyme to examine the molecular basis of AA activity by introducing rational mutations, which identified several active site residues that increase activity with AA. Reversing this approach, we introduced mutations that imparted activity with SA in the maize AAMT, which uncovered different active site residues from those in the citrus enzyme. Sequence and phylogenetic analysis revealed that one of the Vitis AAMTs shares an ancestor with jasmonic acid methyltransferases, similar to the AAMT from strawberry (Frageria sp.). Collectively, these data demonstrate the molecular mechanisms underpinning AA activity across methyltransferases and identify one-step enzymes by which grapes synthesize MeAA.

Variation of vitamin B contents in maize inbred lines: Potential genetic resources for biofortification

Vitamin B and its derivatives possess diverse physiological functions and are essential micronutrients for humans. Their variation in crops is important for the identification of genetic resources used to develop new varieties with enhanced vitamin B. In this research, remarkable variations were observed in kernels of 156 maize inbred lines, ranging from 107.61 to 2654.54 μg per 100 g for vitamin B1, 1.19-37.37 μg per 100 g for B2, 19.60-213.75 μg per 100 g for B3, 43.47-590.86 μg per 100 g for B5, and 138.59-1065.11 μg per 100 g for B6. Growing inbreeds in Hainan and Hebei provinces of China revealed environmental and genotype interactions among these vitamins and the correlations between them in maize grain. Several inbred lines were identified as good sources of vitamin B and promising germplasms for maize breeding, namely By855 and Si273 are overall rich in all the studied vitamins, and GY386B and CML118 are specially enriched with derivatives of vitamin B6. The present study can assist maize breeders with germplasm resources of vitamin B for biofortification to offer people nutritious foods.

Marker-assisted pyramiding of lycopene-ε-cyclase, β-carotene hydroxylase1 and opaque2 genes for development of biofortified maize hybrids

Malnutrition affects growth and development in humans and causes socio-economic losses. Normal maize is deficient in essential amino acids, lysine and tryptophan; and vitamin-A. Crop biofortification is a sustainable and economical approach to alleviate micronutrient malnutrition. We combined favorable alleles of crtRB1 and lcyE genes into opaque2 (o2)-based four inbreds viz. QLM11, QLM12, QLM13, and QLM14 using marker-assisted backcross breeding. These are parents of quality protein maize versions of two elite hybrids viz. Buland and PMH1, grown in India. Gene-based SSRs for o2 and InDel markers for crtRB1 and lcyE were successfully employed for foreground selection in BC₁F₁, BC₂F₁, and BC₂F₂ generations. The recurrent parent genome recovery ranged from 88.9 to 96.0% among introgressed progenies. Kernels of pyramided lines possessed a high concentration of proA (7.14–9.63 ppm), compared to 1.05 to 1.41 ppm in the recurrent parents, while lysine and tryptophan ranged from 0.28–0.44% and 0.07–0.09%, respectively. The reconstituted hybrids (RBuland and RPMH1) showed significant enhancement of endosperm proA (6.97–9.82 ppm), tryptophan (0.07–0.09%), and lysine (0.29–0.43%), while grain yield was at par with their original versions. The dissemination of reconstituted hybrids holds significant promise to alleviate vitamin-A deficiency and protein-energy malnutrition in developing countries.

Development of white-grained PHS-tolerant wheats with high grain protein and leaf rust resistance

The present study involved incorporation of two major QTLs for pre-harvest sprouting tolerance (PHST) in an Indian wheat cultivar named Lok1, which happens to be PHS susceptible. For transfer of two QTLs, two independent programmes with two different donors (AUS1408, CN19055) were utilized. The recipient cv. Lok1 was crossed with each of the two donors, followed by a number of backcrosses. Each backcross progeny was subjected to foreground and background selections. KASP assay was also used for confirming the presence of PHST QTL. In one case, PHST QTL was later also pyramided with a gene for high grain protein content (Gpc-B1) and a gene for leaf rust resistance (Lr24). The MAS derived lines were screened for PHS using simulated rain chambers leading to selection of 10 PHST lines. Four of these advanced lines carried all the three QTL/genes and exhibited high level of PHST (PHS score 2-3) associated with significant improvement in GPC and resistance against leaf rust.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01234-z.