Abstract
Main conclusionThe MIR160 family in Gossypium hirsutum and G. barbadense was characterized, and miR160a_A05 was found to increase cotton-fiber length by downregulating its target gene (ARF17) and several GH3 genes.Cotton fiber is the most important raw material for the textile industry. MicroRNAs are involved in regulating cotton-fiber development, but a role in fiber elongation has not been demonstrated. In this study, miR160a was found to be differentially expressed in elongating fibers between two interspecific (between Gossypium hirsutum and G. barbadense) backcross inbred lines (BILs) with different fiber lengths. The gene MIR160 colocalized with a previously mapped fiber-length quantitative trait locus. Its target gene ARF17 was differentially expressed between the two BILs during fiber elongation, but in the inverse fashion. Bioinformatics was used to analyze the MIR160 family in both G. hirsutum and G. barbadense. Moreover, qRT–PCR analysis identified MIR160a as the functional MIR160 gene encoding the miR160a precursor during fiber elongation. Using virus-induced gene silencing and overexpression, overexpressed MIR160a_A05 resulted in significantly longer fibers compared with wild type, whereas suppression of miR160 resulted in significantly shorter fibers. Expression levels of the target gene auxin-response factor 17 (ARF17) and related genes GH3 in the two BILs and/or the virus-infected plants demonstrated similar changes in response to modulation of miR160a level. Finally, overexpression or suppression of miR160 increased or decreased, respectively, the cellular level of indole-3-acetic acid, which is involved in fiber elongation. These results describe a specific regulatory mechanism for fiber elongation in cotton that can be utilized for future crop improvement.
Highlights
Cotton fiber is the most important source material for the textile industry (Chen et al 2007) and is an ideal model system for cell elongation studies (Kim and Triplett 2001)
MiR160a colocalized with an Fiber length (FL) quantitative trait loci (QTL) and a QTL hotspot that mapped in the backcross inbred lines (BILs) population, including the “Long” and “Short” lines, onto chromosome A05 of the sequenced TM-1 genome (Yu et al 2013)
Our results indicate that the higher expression of miR160a in “Long” compared with “Short” suppresses the expression of its target gene auxin-response factor 17 (ARF17), which in turn downregulates the expression of certain group II glycoside hydrolase family 3 (GH3) genes, leading to higher levels of active Indole-3-acetic acid (IAA) and increased FL
Summary
Cotton fiber is the most important source material for the textile industry (Chen et al 2007) and is an ideal model system for cell elongation studies (Kim and Triplett 2001). Several genes have been shown to affect fiber-cell development, including K + transporters (Ruan et al 2004), sucrose-encoding genes (Ruan et al 2001), and reactive oxygen species–regulated Ca2+ signaling and the vacuolar ( H+)-ATPase (Qin and Zhu 2011) Phytohormones such as auxin (Beasley and Ting 1974; Shindy and Smith 1975; Zhang et al 2011), gibberellin (Beasley and Ting 1974; Gokani and Thaker 2002; Zhang et al 2011), ethylene (Shi et al 2006), brassinosteroid (Sun et al 2004, 2005; Sun and Allen 2005; Shi et al 2006), and cytokinins (Beasley and Ting 1974; Shindy and Smith 1975) play important roles in fiber development. IAA affects fiber-cell elongation in cotton ovules in vitro (Beasley and Ting 1974), and IAA and related auxin metabolites are found in eight DPA fibers (Guinn and Brummett 1988)
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