Abstract
Apoplastic ascorbate oxidase (AO) plays significant roles in plant cell growth. However, the mechanism of underlying the transcriptional regulation of AO in Gossypium hirsutum remains unclear. Here, we obtained a 1,920-bp promoter sequence from the Gossypium hirsutum ascorbate oxidase (GhAO1) gene, and this GhAO1 promoter included a number of known cis-elements. Promoter activity analysis in overexpressing pGhAO1::GFP-GUS tobacco (Nicotiana benthamiana) showed that the GhAO1 promoter exhibited high activity, driving strong reporter gene expression in tobacco trichomes, leaves and roots. Promoter 5’-deletion analysis demonstrated that truncated GhAO1 promoters with serial 5’-end deletions had different GUS activities. A 360-bp fragment was sufficient to activate GUS expression. The P-1040 region had less GUS activity than the P-720 region, suggesting that the 320-bp region from nucleotide -720 to -1040 might include a cis-element acting as a silencer. Interestingly, an auxin-responsive cis-acting element (TGA-element) was uncovered in the promoter. To analyze the function of the TGA-element, tobacco leaves transformed with promoters with different 5’ truncations were treated with indole-3-acetic acid (IAA). Tobacco leaves transformed with the promoter regions containing the TGA-element showed significantly increased GUS activity after IAA treatment, implying that the fragment spanning nucleotides -1760 to -1600 (which includes the TGA-element) might be a key component for IAA responsiveness. Analyses of the AO promoter region and AO expression pattern in Gossypium arboreum (Ga, diploid cotton with an AA genome), Gossypium raimondii (Gr, diploid cotton with a DD genome) and Gossypium hirsutum (Gh, tetraploid cotton with an AADD genome) indicated that AO promoter activation and AO transcription were detected together only in D genome/sub-genome (Gr and Gh) cotton. Taken together, these results suggest that the 1,920-bp GhAO1 promoter is a functional sequence with a potential effect on fiber cell development, mediated by TGA-element containing sequences, via the auxin-signaling pathway.
Highlights
Upland cotton (Gossypium hirsutum L.) is an important economic crop worldwide and occupies a vital position in the global economy as its fibers are the most important plant materials for the textile industry [1]
GhAO1 was accumulated during fiber fast elongation development stages (5–20 dpa) in widetype (WT) cotton ovules associated with fibers compared with 10-dpa fuzzless-lintless mutant ovules, both at mRNA level and enzyme activity (S1 Fig)
ascorbate oxidase (AO) is highly expressed in fast-growing organs, indicating a direct link between AO and cell development through regulating redox balance regulation of the apoplast [18]
Summary
Upland cotton (Gossypium hirsutum L.) is an important economic crop worldwide and occupies a vital position in the global economy as its fibers are the most important plant materials for the textile industry [1]. The plant hormone auxin performs a decisive function in fiber development by regulating extracellular oxidative signals that affect cell wall configuration [3,4,5]. As a member of a small multigene family of multicopper oxidases, ascorbate oxidase (AO; EC 1.10.3.3) catalyzes the oxidation of ascorbic acid (AA) to dehydroascorbate (DHA), thereby generating oxidative signals in apoplasts [6,7,8]. DHA is an important oxidative molecule in apoplasts, and many studies have suggested that the oxidative signal catalyzed by AO plays a crucial role in cell elongation and enlargement [9]. AO is strongly expressed in the stretch expanded fruit of cucurbitaceous plants, including cucumber, pumpkin and melon. AO expression is promptly increased during callus growth, fruit development and seedling elongation [9,10]. AO is abundantly expressed in the young and growing tissues of tobacco [6,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
