Abstract
Cotton fibres, as single cells arising from the seed coat, can be classified as lint and fuzz according to their final length. Gossypium arboreum is a cultivated diploid cotton species and a potential donor of the A subgenome of the more widely grown tetraploid cottons. In this study, we performed genetic studies on one lintless and seven fuzzless G. arboreum accessions. Through association and genetic linkage analyses, a recessive locus on Chr06 containing GaHD-1 was found to be the likely gene underlying the lintless trait. GaHD-1 carried a mutation at a splicing acceptor site that resulted in alternative splicing and a deletion of 247 amino acid from the protein. The regions containing GaGIR1 and GaMYB25-like were found to be associated with fuzz development in G. arboreum, with the former being the major contributor. Comparative transcriptome analyses using 0-5 days post-anthesis (dpa) ovules from lintless, fuzzless, and normal fuzzy seed G. arboreum accessions revealed gene modules and hub genes potentially important for lint and fuzz initiation and development. Three significant modules and 26 hub genes associated with lint fibre initiation were detected by weighted gene co-expression network analysis. Similar analyses identified three vital modules and 10 hub genes to be associated with fuzz development. The findings in this study contribute to understanding the complex molecular mechanism(s) regulating fibre initiation and development and indicate that G. arboreum may have fibre developmental pathways different from tetraploid cotton. It also provides candidate genes for further investigation into modifying fibre development in G. arboreum.
Highlights
Cotton, widely grown in more than 70 countries, is the world’s leading textile crop and an important source of plant oil and protein [1]
We examined a lintless/glabrous and seven fuzzless G. arboreum accessions to investigate the genetics of the lintless and fuzzless traits and to uncover the underlying gene(s) responsible for these traits
Possible explanations for the observed difference between the G. arboruem and tetraploid function of HD-1 is that there is some low threshold in the expression of GhHD-1 in the seed coat epidermis required for lint fibre initiation and development or, possibly, that the seed fibre pathways may be regulated differently between the diploid and tetraploid cottons, with the tetraploid species having unknown genetic component(s) that can compensate for the loss-of-function of HD-1
Summary
Widely grown in more than 70 countries, is the world’s leading textile crop and an important source of plant oil and protein [1]. There are four cultivated cotton species, including two diploid species, Gossypium herbaceum (A1) and G. arboreum (A2), and two tetraploid species, G. hirsutum (AD) and G. barbadense (AD)2 [2]. G. arboreum, as a putative donor of the A subgenome of the tetraploid cottons, is a good model species for studies of cotton genomics and genetics, as evaluating molecular mechanisms and physiological factors are simplified in diploid species compared to the tetraploid species [3,6]. Cotton plants vary in the density of trichomes on different vegetative parts, from being highly pubescent to glabrous. It has been shown that cotton species with glabrous leaves and stems, for example, produce cleaner cotton lint and can reduce oviposition by some insect pests [9,10,11,12]. The silencing of GhHD-1 by RNAi significantly reduced trichome density and delayed the timing of fibre initiation, indicating that the underlying mechanisms regulating trichome and fibre initiation might share some common pathways [15]
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