Abstract
Auxin plays a key role in different plant growth and development processes, including flower opening and development. The perception and signaling of auxin depend on the cooperative action of various components, among which auxin/indole-3-acetic acid (Aux/IAA) proteins play an imperative role. In a recent study, the entire Aux/IAA gene family was identified and comprehensively analyzed in Hedychium coronarium, a scented species used as an ornamental plant for cut flowers. Phylogenetic analysis showed that the Aux/IAA gene family in H. coronarium is slightly contracted compared to Arabidopsis, with low levels of non-canonical proteins. Sequence analysis of promoters showed numerous cis-regulatory elements related to various phytohormones. HcIAA genes showed distinct expression patterns in different tissues and flower developmental stages, and some HcIAA genes showed significant responses to auxin and ethylene, indicating that Aux/IAAs may play an important role in linking hormone signaling pathways. Based on the expression profiles, HcIAA2, HcIAA4, HcIAA6 and HcIAA12, were selected as candidate genes and HcIAA2 and HcIAA4 were screened for further characterization. Downregulation of HcIAA2 and HcIAA4 by virus-induced gene silencing in H. coronarium flowers modified the total volatile compound content, suggesting that HcIAA2 and HcIAA4 play important roles in H. coronarium floral scent formation. The results presented here will provide insights into the putative roles of HcIAA genes and will assist the elucidation of their precise roles during floral scent formation.
Highlights
Auxin plays a substantial role in several aspects of plant growth and development, like cell division, apical dominance, vascular differentiation, lateral/adventitious root formation and fruit and flower development [1,2,3]
auxin/indole-3-acetic acid (Aux/IAA) proteins are normally conserved with four domains known as domain I to domain IV, proteins missing one or two domains were included in this gene family [1]
Our results revealed that ethylene responsive elements were enriched in most promoters of HcIAA genes (18 out of 27), suggesting that auxin and ethylene play key roles through cross-talk via HcIAAs in H. coronarium flowers; this result is similar to that found in tomato, in which the same pattern was reported, and 16 out of the 25 Sl-IAA promoters contained ethylene-response motifs [37]
Summary
Auxin plays a substantial role in several aspects of plant growth and development, like cell division, apical dominance, vascular differentiation, lateral/adventitious root formation and fruit and flower development [1,2,3]. Aux/IAAs inactivate ARFs, which can be either transcriptional repressors or activators of primary auxin-responsive genes [6,7]. To regulate auxin-responsive genes, Aux/IAA proteins do not bind directly to AuxREs; they interact with ARFs by controlling ARF activity [18]. Aux/IAA plays a key role in monocots and dicots plants by affecting the development of flowers, roots and stems. It affects some secondary metabolism, such as the biosynthesis of volatile compounds [22,23,24]. We identified Aux/IAA family genes in H. coronarium genomes and analyzed their sequence characteristics, genomic structures, phylogeny and cis-regulatory elements. Our findings will provide novel insights into the functions of Aux/IAA and will assist scientists in future studies on elucidating the precise biological functions of Aux/IAA genes in H. coronarium
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