Abstract
The PIN-FORMED (PIN) protein, the most important polar auxin transporter, plays a critical role in the distribution of auxin and controls multiple biological processes. However, characterizations and functions of this gene family have not been identified in cotton. Here, we identified the PIN family in Gossypium hirsutum, Gossypium arboreum, and Gossypium raimondii. This gene family was divided into seven subgroups. A chromosomal distribution analysis showed that GhPIN genes were evenly distributed in eight chromosomes and that the whole genome and dispersed duplications were the main duplication events for GhPIN expansion. qRT-PCR analysis showed a tissue-specific expression pattern for GhPIN. Likely due to the cis-element variations in their promoters, transcripts of PIN6 and PIN8 genes from the At (tetraploid genome orginated from G. arboreum) subgenome and PIN1a from the Dt (tetraploid genome orginated from G. raimondii) subgenome in G. hirsutum was significantly increased compared to the transcripts in the diploids. The differential regulation of these PIN genes after the polyploidization may be conducive to fiber initiation and elongation. Exogenously applied auxin polar transport inhibitor significantly suppressed fiber growth, which is consistent with the essential function of these PIN genes for regulating cotton fiber development. Furthermore, the overexpression of GhPIN1a_Dt, GhPIN6_At, and GhPIN8_At in Arabidopsis promoted the density and length of trichomes in leaves.
Highlights
The plant phytohormone, auxin, plays a crucial role in various developmental processes, such as root development, apical dominance, embryo formation, vascular differentiation, tropism, and plant response to internal and external stimuli (Dubrovsky et al, 2008; Mashiguchi et al, 2011; Rakusova et al, 2015; Wang H.Z. et al, 2015; Xi et al, 2016)
To identify all of the PIN proteins in G. hirsutum (AADD genome) and its two diploid ancestors, G. arboreum (AA genome) and G. raimondii (DD genome), we used the Arabidopsis PIN protein sequences to query the three reference genomes to screen out candidate PIN-like proteins in cotton
Compared with the transgenic line carrying the empty vector, the 35S::GhPIN1a_Dt, 35S::GhPIN6_At or 35S::GhPIN8_At displayed longer trichomes in the leaves (Figure 6F). These results suggest that the GhPIN1a_Dt, GhPIN6_At and GhPIN8_At genes possess biological activity for cell elongation in vivo, which strongly suggests that the high expression of the three PINs in G. hirsutum contributes to cotton fiber development
Summary
The plant phytohormone, auxin, plays a crucial role in various developmental processes, such as root development, apical dominance, embryo formation, vascular differentiation, tropism, and plant response to internal and external stimuli (Dubrovsky et al, 2008; Mashiguchi et al, 2011; Rakusova et al, 2015; Wang H.Z. et al, 2015; Xi et al, 2016). The asymmetric distribution of auxin, which is largely dependent on an active process called directional polar auxin transport (PAT) mediated by influx and efflux carriers, has been confirmed to play a vital role in controlling plant growth and development (Friml, 2003; Wang et al, 2008; Band et al, 2014; D’Alessandro et al, 2015; Yang et al, 2015). PIN-LIKES (PILS) family, which are localized to the endoplasmic reticulum and involved in the regulation of intracellular auxin homeostasis, was characterized as a novel putative auxin carriers (Barbez et al, 2012; Feraru et al, 2012)
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