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. 2019 Oct 25:10:1346.
doi: 10.3389/fpls.2019.01346. eCollection 2019.

Seed Coat Pattern QTL and Development in Cowpea (Vigna unguiculata [L.] Walp.)

Ira A Herniter  1 , Ryan Lo  1 , María Muñoz-Amatriaín  1 , Sassoum Lo  1 , Yi-Ning Guo  1 , Bao-Lam Huynh  2 , Mitchell Lucas  1 , Zhenyu Jia  1 , Philip A Roberts  2 , Stefano Lonardi  3 , Timothy J Close  1
Affiliations

Seed Coat Pattern QTL and Development in Cowpea (Vigna unguiculata [L.] Walp.)

Ira A Herniter et al. Front Plant Sci. .

Erratum in

Abstract

The appearance of the seed is an important aspect of consumer preference for cowpea (Vigna unguiculata [L.] Walp.). Seed coat pattern in cowpea has been a subject of study for over a century. This study makes use of newly available resources, including mapping populations, a reference genome and additional genome assemblies, and a high-density single nucleotide polymorphism genotyping platform, to map various seed coat pattern traits to three loci, concurrent with the Color Factor (C), Watson (W), and Holstein (H) factors identified previously. Several gene models encoding proteins involved in regulating the later stages of the flavonoid biosynthesis pathway have been identified as candidate genes, including a basic helix-loop-helix gene (Vigun07g110700) for the C locus, a WD-repeat gene (Vigun09g139900) for the W locus and an E3 ubiquitin ligase gene (Vigun10g163900) for the H locus. A model of seed coat development, consisting of six distinct stages, is described to explain some of the observed pattern phenotypes.

Keywords: Vigna unguiculata; cowpea; pattern; pigment; quantitative trait loci; seed coat.

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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
Seed coat pattern traits. Images of lines from various populations demonstrating the phenotypes which were scored as part of this study.
Figure 2
Figure 2
Interaction of seed coat pattern loci. (A) Table displaying the pattern loci identified in mapping, their locations, the trait encoded, alleles identified, and phenotypes. (B) Table displaying the allelic series and relative dominance of alleles. (C) Segregation patterns for the CB27 by BB and CB27 by 556 F8 populations. (D) Segregation patterns for the CB46 by 503 and 524B by 2049 F8 populations. (E) Segregation pattern for the Tvu-15426 by MAGIC014 F2 populations. (F) Segregation pattern for the CB27 by B21 and B21 by CB50 F2 populations. (G) Phenotype of seeds from the F1 plants resulting from a series of crosses (i) Cross between CB27 and line from the CB27 by BB population with a Watson pattern, resulting in Watson pattern. (ii) Cross between CB27 and a line from the CB27 by BB population a Holstein pattern, resulting in Holstein pattern. (iii) Cross between CB27 and a line from the CB27 by BB population with a Full Coat pattern, resulting in a Full Coat pattern. (iv) Cross between IT84S-2246 and IT93K-503-1 from the early development of the MAGIC population, resulting in a Full Coat pattern in the seed coats on seeds of the F1 maternal parent.
Figure 3
Figure 3
Seed coat color development. Images showing the development the seed and the spread of pigmentation.
Figure 4
Figure 4
Proposed roles of the C, W, and H genes. Transcription of flavonoid biosynthesis pathway genes are controlled by a complex composed of three types of proteins (Xu et al., 2015), a basic helix-loop-helix protein (bHLH; e.g., Vigun07g110700, C locus), a WD-repeat protein (WD40; e.g., Vigun09g139900, W locus), and an R2R3 MYB transcription factor. This complex is in turn negatively regulated by an E3 Ubiquitin ligase (E3UL; e.g., Vigun10g163900, H locus). Sequence comparisons suggest that bHLH transcription may be controlled by ERF and WRKY proteins. The observed seed coat pattern phenotypes are a result of different alleles and expression patterns.
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