Genetic analysis of the Arabidopsis TIR1/AFB auxin receptors reveals both overlapping and specialized functions

Abstract

The TIR1/AFB auxin co-receptors mediate diverse responses to the plant hormone auxin. The Arabidopsis genome encodes six TIR1/AFB proteins representing three of the four clades that were established prior to angiosperm radiation. To determine the role of these proteins in plant development we performed an extensive genetic analysis involving the generation and characterization of all possible multiply-mutant lines. We find that loss of all six TIR1/AFB proteins results in early embryo defects and eventually seed abortion, and yet a single wild-type allele of TIR1 or AFB2 is sufficient to support growth throughout development. Our analysis reveals extensive functional overlap between even the most distantly related TIR1/AFB genes except for AFB1. Surprisingly, AFB1 has a specialized function in rapid auxin-dependent inhibition of root growth and early phase of root gravitropism. This activity may be related to a difference in subcellular localization compared to the other members of the family.

Auxin-induced signaling protein nanoclustering contributes to cell polarity formation

“…We next investigated how auxin promotes the formation and polarization of ordered lipid domains to the indenting region. Auxin signaling is mediated by at least two major pathways: the nuclear-based TIR1/AFB pathway that regulates the expression of auxininduced genes 19,20 and the PM-based TMK pathway involved in both transcriptional and non-transcriptional auxin responses 21,22 . Because auxin promotes ROP6 activation in a TMK-dependent manner 21,25 , we speculated that the TMKdependent pathway regulates lipid ordering and its polarity.…”

“…Auxin, a highly diffusible small-molecule hormone known to regulate cell polarity 18 , impacts virtually every aspect of plant growth and development via nuclear gene transcription and rapid non-transcriptional responses controlled by the nuclear/cytoplasmic TIR1/AFB auxin receptors 19,20 , as well as those mediated by the PM-localized transmembrane kinases (TMKs) 21,22 . Auxininduced activation of ROPs is involved in cellular symmetry breaking such as polarization of PIN proteins, which export auxin 21,23 , and the morphogenesis of Arabidopsis thaliana leaf and cotyledon pavement cells (PCs) 21,24,25 .…”

CLAVATA Signaling Ensures Reproductive Development in Plants across Thermal Environments

“…Higher temperatures also enhance penetrance of seedling defects in loss-of-function mutants in the TRANSPORT INHIBITOR RESPONSE1 (TIR)-family auxin receptors. 50 As such, heat might have an unappreciated negative impact on auxin function, with thermomorphogenesis-induced auxin playing a protective role rather than simply directing growth. How CLV2/CRN stimulate auxin-dependent flower initiation is unknown.…”

Auxin: Hormonal Signal Required for Seed Development and Dormancy

“…More specifically, PIN7 is suspensor specific and is polarized toward the proembryo, where the auxin response maximum is established [ 67 ]; (iii) TAA1 and YUC1 , 4 genes are expressed in few apical cells of globular proembryo state (16-cell embryo), constituting another place of auxin accumulation and triggers polarization of the PIN1 proteins, but not auxin signaling. These processes contribute to the specification of the proembryo basal pole; (iv) the findings (ii) and (iii) generate an apical-basal auxin gradient provoked by the polarized localization of the auxin efflux transporters PIN1 in Arabidopsis and maize [ 55 , 80 ] and PIN7 in Arabidopsis [ 55 ]; (v) additionally, at a late globular stage, YUC1 and YUC4 were expressed in the same embryonic apical area, and YUC8 was detected closer to the root pole. Mutations in YUC8 lead to mitotic arrest during female gametophyte development; (vi) loss of function of TAA1 / TAR and YUC genes greatly disturbs embryo development [ 72 ].…”