Abstract
BackgroundThe phytohormone auxin mediates a stunning array of plant development through the functions of AUXIN RESPONSE FACTORs (ARFs), which belong to transcription factors and are present as a protein family comprising 10–43 members so far identified in different plant species. Plant development is also subject to regulation by TRANSPARENT TESTA GLABRA (TTG) proteins, such as NtTTG2 that we recently characterized in tobacco Nicotiana tabacum. To find the functional linkage between TTG and auxin in the regulation of plant development, we performed de novo assembly of the tobacco transcriptome to identify candidates of NtTTG2-regulated ARF genes.ResultsThe role of NtTTG2 in tobacco growth and development was studied by analyzing the biological effects of gene silencing and overexpression. The NtTTG2 gene silencing causes repressive effects on vegetative growth, floral anthocyanin synthesis, flower colorization, and seed production. By contrast, the plant growth and development processes are promoted by NtTTG2 overexpression. The growth/developmental function of NtTTG2 associates with differential expression of putative ARF genes identified by de novo assembly of the tobacco transcriptome. The transcriptome contains a total of 54,906 unigenes, including 30,124 unigenes (54.86%) with annotated functions and at least 8,024 unigenes (14.61%) assigned to plant growth and development. The transcriptome also contains 455 unigenes (0.83%) related to auxin responses, including 40 putative ARF genes. Based on quantitative analyses, the expression of the putative genes is either promoted or inhibited by NtTTG2.ConclusionsThe biological effects of the NtTTG2 gene silencing and overexpression suggest that NtTTG2 is an essential regulator of growth and development in tobacco. The effects of the altered NtTTG2 expression on expression levels of putative ARF genes identified in the transcriptome suggest that NtTTG2 functions in relation to ARF transcription factors.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-14-806) contains supplementary material, which is available to authorized users.
Highlights
The phytohormone auxin mediates a stunning array of plant development through the functions of AUXIN RESPONSE FACTORs (ARFs), which belong to transcription factors and are present as a protein family comprising 10–43 members so far identified in different plant species
The repressive effect of NtTTG2 silencing on the vegetative growth and the development of flowers and seeds in tobacco To elucidate the roles of NtTTG2 in the growth and development of tobacco N. tabacum, we generated the NtTTG2-silencing line TTG2RNAi4 under background of the N. tabacum variety NC89 and observed its growth and development in contrast to the wild-type (WT) phenotype
We investigated the vegetative growth of WT RFP and TTG2RNAi4 plants on Murashige and Skoog (MS) agar medium and in pots
Summary
The phytohormone auxin mediates a stunning array of plant development through the functions of AUXIN RESPONSE FACTORs (ARFs), which belong to transcription factors and are present as a protein family comprising 10–43 members so far identified in different plant species. TTGs are characterized by the presence of the WD40 motif [5,6,7], which refers to the conserved tryptophan (W) and aspartate (D) dipeptide and the length of approximately 40 amino acid residues in a protein sequence [8] This motif is present as a series of repeats to form protein interaction domain in a variety of proteins [9,10,11], including all TTGs so far Depending on natures of interacted proteins, TTGs differentiate their functions between development and defense regulations [6,16]. NtTTG2 does not interact with NPR1 but is able to sequester NPR1 from the nucleus, preventing NPR1 from transcriptional regulation of defense responses [5] These studies suggest that TTGs regulate specific processes of development or defenses by either directly or indirectly interacting with other proteins involved in the processes. Whether NtTTG2 plays a role in development regulation was unclear
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