Abstract
Auxins are one of the most important and studied phytohormones in nature. Auxin signaling and perception take place in the cytosol, where the auxin is sensed. Then, in the nucleus, the auxin response factors (ARF) promote the expression of early-response genes. It is well known that not all plants respond to the same amount and type of auxins and that the response can be very different even among plants of the same species, as we present here. Here we investigate the behavior of ARF in response to various auxins in Agave angustifolia Haw., A. fourcroydes Lem. and A. tequilana Weber var. Azul. By screening the available database of A. tequilana genes, we have identified 32 ARF genes with high sequence identity in the conserved domains, grouped into three main clades. A phylogenetic tree was inferred from alignments of the 32 Agave ARF protein sequences and the evolutionary relationship with other species was analyzed. AteqARF 4, 15, 21, and 29 were selected as a representative diverse sample coming from each of the different subclades that comprise the two main clades of the inferred phylogenetic reconstruction. These ARFs showed differential species-specific expression patterns in the presence of indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D). Interestingly, A. angustifolia showed different phenotypes in the presence and absence of auxins. In the absence of auxin, A. angustifolia produces roots, while shoots are developed in the presence of IAA. However, in the presence of 2,4-D, the plant meristem converts into callus. According to our results, it is likely that AteqARF15 participates in this outcome.
Highlights
Auxins are a very simple group of plant growth regulators with a very complex set of activities[1]
We found that the 23 auxin response factors (ARF) in Agave can be grouped in these three major clades (Fig. 2)
We found that AteqARF15 was in the same clade as ARF27 of Z. mays, ARF7 of Solanum lycopersicum, ARF7 and 19 of A. thaliana, ARF10 of V. vinifera and ARF3 of C. sativus (Fig. 3)
Summary
Auxins are a very simple group of plant growth regulators with a very complex set of activities[1]. Domains III and IV work like a domain of protein-protein interaction allowing the formation of homo- and heterodimers among Aux/IAA and repressing the activity of the Auxin Response Factors (ARFs)[26,29]. In an Arabidopsis transcriptomic study, Paponov et al.[42] found that in response to different concentrations of auxins, from very low (0.1 μM) to very high (10 μM), ARFs 4, 16 and 19 were up-regulated in response to auxin. The aim of this work is to determine how different auxins affect the growth and phenotype of different Agave species (A. angustifolia, A. fourcroydes and A. tequilana) and to elucidate the effects on short- and long-term cultivation of IAA and 2,4-D targeted toward two ARF with domains related to repression, AteqARF4 and 21, and two ARF related to the activation of expression, AteqARF15 and 29
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