Abstract
Diverse leaf morphology has been observed among accessions of Gossypium hirsutum, including okra leaf, which has advantages and disadvantages in cotton production. The okra leaf locus has been mapped to chromosome 15 of the Dt subgenome, but the underlying gene has yet to be identified. In this study, we used a combination of targeted association analysis, F2 population-based fine mapping, and comparative sequencing of orthologues to identify a candidate gene underlying the okra leaf trait in G. hirsutum. The okra leaf gene identified, GhOKRA, encoded a homeodomain leucine-zipper class I protein, whose closely related genes in several other plant species have been shown to be involved in regulating leaf morphology. The transcript levels of GhOKRA in shoot apices were positively correlated with the phenotypic expression of the okra leaf trait. Of the multiple sequence variations observed in the coding region among GrOKRA of Gossypium raimondii and GhOKRA-Dt of normal and okra/superokra leaf G. hirsutum accessions, a non-synonymous substitution near the N terminus and the variable protein sequences at the C terminus may be related to the leaf shape difference. Our results suggest that both transcription and protein activity of GhOKRA may be involved in regulating leaf shape. Furthermore, we found that non-reciprocal homoeologous recombination, or gene conversion, may have played a role in the origin of the okra leaf allele. Our results provided tools for further investigating and understanding the fundamental biological processes that are responsible for the cotton leaf shape variation and will help in the design of cotton plants with an ideal leaf shape for enhanced cotton production.
Highlights
Leaves are the main photosynthetic organs of vascular insect pests, evapotranspiration, and pest preference, and plants
The plant materials used in this study comprised: 177 accessions of G. hirsutum (AD1) ( Supplementary Table S1 at JXB online); two F2 populations segregating for the okra leaf trait, the first containing 1873 (448 okra:964 subokra:461 normal) individuals derived from RIL034 [okra leaf, derived from T586×Yumian1 (Zhang et al, 2009)]×Yumian1, and the second containing 310 (72 okra:142 subokra:96 normal) individuals derived from RIL090×Jinnong08; three accessions of G. barbadense (AD2); three accessions of G. arboreum (A2); and a G. arboreum F2 population (68 plants) derived from Yunnanzhongmian (YZ)×BM13H
We identified GhOKRA-Dt, which encodes an homeodomain leucine-zipper (HD-Zip) class I protein, as the best candidate gene determining the okra leaf trait in G. hirsutum
Summary
Leaves are the main photosynthetic organs of vascular insect pests, evapotranspiration, and pest preference, and plants. Two A-genome diploid species [Gossypium arboreum (A2) and Gossypium herbaceum (A1)] and two AD-genome tetraploid species [Gossypium hirsutum (AD1) and Gossypium barbadense (AD2)] were independently domesticated and are cultivated for their fibres (Wendel, 1989). Cultivated cottons are dominated by G. hirsutum and to a much lesser extent G. barbadense, which are thought to have originated from relatively recent interspecific hybridization events between an A-genome-like ancestral species similar to modern G. arboreum or G. herbaceum and a D-genome-like species similar to modern Gossypium raimondii (D5; Wendel and Cronn, 2003). The leaf shape of most of the G. hirsutum, or upland cotton, varieties is designated as normal or palmate with from three to five rather shallow sinuses, but other leaf shapes such as subokra, okra and superokra with variable depth of indentations exist. The leaf shape of G. barbadense is defined as Sea Island-type, and is similar to subokra observed in G. hirsutum, having moderate indentations
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