The cyclophilin DIAGEOTROPICA has a conserved role in auxin signaling

Abstract

SUMMARYAuxin has a fundamental role throughout the life cycle of land plants. Previous studies showed that the tomato cyclophilin DIAGEOTROPICA (DGT) promotes auxin response, but its specific role in auxin signaling remains unknown. We sequenced candidate genes in auxin-insensitive mutants of Physcomitrella patens and identified mutations in highly conserved regions of the moss ortholog of tomato DGT. As P. patens and tomato diverged from a common ancestor more than 500 million years ago, this result suggests a conserved and central role for DGT in auxin signaling in land plants. In this study we characterize the P. patens dgt (Ppdgt) mutants and show that their response to auxin is altered, affecting the chloronema-to-caulonema transition and the development of rhizoids. To gain an understanding of PpDGT function we tested its interactions with the TIR1/AFB-dependent auxin signaling pathway. We did not observe a clear effect of the Ppdgt mutation on the degradation of Aux/IAA proteins. However, the induction of several auxin-regulated genes was reduced. Genetic analysis revealed that dgt can suppress the phenotype conferred by overexpression of an AFB auxin receptor. Our results indicate that the DGT protein affects auxin-induced transcription and has a conserved function in auxin regulation in land plants.

Peptidyl-prolyl isomerization targets rice Aux/IAAs for proteasomal degradation during auxin signalling

“…Considering that the key components, including LRT2-like proteins and Aux/IAAs, are highly conserved in both lower and higher plants and that the loss-of-function mutations in tomato DGT and moss PpDGT cause a similar auxin-insensitive phenotype 29,30 , the cyclophilin-catalysed isomerization of the Aux/IAA transcriptional repressors may represent a general mechanism in regulating auxin signalling in the plant kingdom. In agreement with this notion, LRT2/OsCYP2 was found to directly interact with OsSGT1 (suppressor of G2 allele of skp1) 17 , whose Arabidopsis homologous gene AtSGT1b was identified from a genetic screen for the enhancers of tir1-1 and was characterized as co-chaperone to be required for the SCF TIR1 -mediated degradation of Aux/IAA proteins 39 .…”

“…Gly 72 is a highly conserved residue located in the PPIase domain ( Supplementary Fig. 6a) and mutations in this residue of rice LRT2/OsCYP2 and moss PpDGT cause severely impaired auxin signalling 17,30 . Homologous structure modelling based on the crystal structure of wheat (Triticum aestivum) TaCypA-1 (PDB code: 4E1Q) 34 , a cyclophilin sharing 87% identity with LRT2, revealed that Gly 72 is located at the surface of LRT2 immediately adjacent to a b-sheet ( Supplementary Fig.…”

“…A number of plant CYP genes, mainly in Arabidopsis, have been functionally characterized, involved in a variety of physiological and developmental processes, including in flowering, phytohormone signalling, stress responses and immune responses [22][23][24][25][26][27] . Mutations in LRT2-like genes of the tomato DIAGEOTROPICA (DGT) and the moss Physcomitrella patens PpDGT genes also caused an auxin-resistant phenotype [28][29][30] , indicating that this class of highly conserved genes plays an important role in regulating auxin signalling in both lower and higher plants. However, how the cyclophilin-type PPIases function in auxin signalling remains unknown.…”

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

“…The unusual FK506-binding domain in TWD1 was instead found to participate in protein interaction with ABCB-type auxin transporters and is apparently involved in the functional regulation of these transporters [44] (see Section 4). TWD1 also possesses a tetratricopeptide repeat domain (common [131] Regulation and PM-to-ER trafficking of ABCB-type auxin transporters [8,9] Z. mais [133] Interaction with ABCB transporters on PM (via FKB-domain) [8,62], ABCC transporters on tonoplast (via TPR domain) [66], with HSP90 (TPR domain) [62,65] and calmodulin (calmodulin-binding domain) [66] Over-expression of TWD1 lacking its membrane anchor results in hypermorphic growth [64] FKBP72/PAS1 A. thaliana [69] Unclear (C-terminal membrane anchor), nuclear [68,134] Low, inhibited by FK506 and rapamycin [134] Up-regulated cell division, leaf fusions, short hypocotyls, sterile [69] O. sativa [131] Chaperon during translocation of NAC-like transcription factor (AtFAN) into nucleus [68] Z. mais [133] Regulation of very long fatty acid elongation [70] -DGT/CypA/ROC1/CYP1/CYP2/ P. patens [10] Nuclear and cytoplasmic [10,90], phloem sieve elements [79] Significant [77,78], inhibited by CsA [78] Regulates growth [90], gene expression [84,90,92], patterned cell division [88], phloem function [79], ROS balance in root apical meristem [87] A. [137] in many large immunophilins) that was shown to interact with vacuolar ABC transporters of the C subclass and HSP90 [65,66], as w...…”

“…2), and can move from shoot to root in grafted plants partially restoring the lack of lateral roots in dgt mutant rootstocks [89]. A DGT-like small cyclophilin from Physcomitrella patens is also important for auxin-regulated growth [90], whereas a related cyclophilin from rice (LATERAL ROOTLESS2, LRT2/OsCYP2) plays a crucial role in auxin-regulated lateral root formation [91] and has been shown to directly regulate the stability of the auxin-responsive transcriptional repressor protein, OsIAA11, via peptidylprolyl isomerization [92]. The Arabidopsis cyclophilin CYCLOPHILIN20-2 regulates flowering time by modulating the conformation of BRASSINAZOLE-RESISTANT1 in Ref.…”