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Review
. 2023 Sep 19:14:1249230.
doi: 10.3389/fpls.2023.1249230. eCollection 2023.

Genetic and molecular understanding for the development of methionine-rich maize: a holistic approach

Veena Devi  1 , Bharat Bhushan  1 , Mamta Gupta  2 , Mehak Sethi  1 , Charanjeet Kaur  3 , Alla Singh  2 , Vishal Singh  4 , Ramesh Kumar  4 , Sujay Rakshit  4 , Dharam P Chaudhary  1
Affiliations
Review

Genetic and molecular understanding for the development of methionine-rich maize: a holistic approach

Veena Devi et al. Front Plant Sci. .

Abstract

Maize (Zea mays) is the most important coarse cereal utilized as a major energy source for animal feed and humans. However, maize grains are deficient in methionine, an essential amino acid required for proper growth and development. Synthetic methionine has been used in animal feed, which is costlier and leads to adverse health effects on end-users. Bio-fortification of maize for methionine is, therefore, the most sustainable and environmental friendly approach. The zein proteins are responsible for methionine deposition in the form of δ-zein, which are major seed storage proteins of maize kernel. The present review summarizes various aspects of methionine including its importance and requirement for different subjects, its role in animal growth and performance, regulation of methionine content in maize and its utilization in human food. This review gives insight into improvement strategies including the selection of natural high-methionine mutants, molecular modulation of maize seed storage proteins and target key enzymes for sulphur metabolism and its flux towards the methionine synthesis, expression of synthetic genes, modifying gene codon and promoters employing genetic engineering approaches to enhance its expression. The compiled information on methionine and essential amino acids linked Quantitative Trait Loci in maize and orthologs cereals will give insight into the hotspot-linked genomic regions across the diverse range of maize germplasm through meta-QTL studies. The detailed information about candidate genes will provide the opportunity to target specific regions for gene editing to enhance methionine content in maize. Overall, this review will be helpful for researchers to design appropriate strategies to develop high-methionine maize.

Keywords: QTLs; maize; methionine; poultry feed; sulphur metabolism; δ-zein.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Overview of sulphur assimilation, methionine synthesis and its storage (1: ATP Sulfurylase, 2: APS Reductase, 3: Sulfite Reductase, 4: OAS thiol-lyase).
Figure 2
Figure 2
Methionine biosynthesis and metabolism: Diagram of metabolic pathway showing aspartate family pathway, metabolism of methionine and cysteine biosynthesis. Dashed arrows represent feedback inhibition of key enzymes. The bold dashed and dotted arrow represents the stimulation of threonine synthase activity through SAM. (Amir, 2008). DHPS, dihydrodipicolinate synthase; AK, aspartate kinase; HK, homoserine kinase; TS, threonine synthase; HSD, homoserine dehydrogenase; SAT, serine acetyl transferase; TDH, threonine dehydratase; OAS (thio) lyase, O-acetyl serine (thio) lyase; CBL, cystathionine-β-lyase; CGS, cystathionine-γ-synthase; SAM, S-adenosyl methionine; MS, methionine synthase; AdoHcys, adenosylhomocysteine; SAMS, S-adenosyl methionine synthase; SMM, S-methylmethionine; MTHF, methyltetrahydrofolate.
Figure 3
Figure 3
Flow diagram representing target key enzymes for genetic engineering to enhance Met expression. AK, aspartate kinase; SAT, serine acetyl transferase; APS Reductase, adenosine 5-adenylylsulfate Reductase; APS, adenosine 5-adenylylsulfate; CGS, cystathionine-γ-synthase; TS, threonine synthase; MS, methionine synthase; SAMS, S-adenosyl methionine synthase.
Figure 4
Figure 4
Different approaches and targets for the enhanced accumulation of methionine in maize.
See this image and copyright information in PMC

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