AUXIN RESPONSE FACTOR 2 (ARF2): a pleiotropic developmental regulator

Abstract

SummaryAUXIN RESPONSE FACTORS (ARFs) regulate auxin-mediated transcriptional activation/repression. They are encoded by a gene family in Arabidopsis, and each member is thought to play a central role in various auxinmediated developmental processes. We have characterized three arf2 mutant alleles, arf2-6, arf2-7 and arf2-8. The mutants exhibit pleiotropic developmental phenotypes, including large, dark green rosette leaves, delayed flowering, thick and long inflorescence, abnormal flower morphology and sterility in early formed flowers, large organ size and delayed senescence and abscission, compared with wild-type plants. In addition, arf2 mutant seedlings have elongated hypocotyls with enlarged cotyledons under various light conditions. The transcription of ACS2, ACS6 and ACS8 genes is impaired in the developing siliques of arf2-6. The phenotypes of all three alleles are similar to those of the loss-of-function mutants obtained by RNA interference or co-suppression. There is no significant effect of the mutation on global auxin-regulated gene expression in young seedlings, suggesting that ARF2 does not participate in auxin signaling at that particular developmental stage of the plant life cycle. Because ARF2 is thought to function as a transcriptional repressor, the prospect arises that its pleiotropic effects may be mediated by negatively modulating the transcription of downstream genes in signaling pathways that are involved in cell growth and senescence.

A Genome-Wide Chronological Study of Gene Expression and Two Histone Modifications, H3K4me3 and H3K9ac, during Developmental Leaf Senescence

“…Auxin synthesis sets in motion major changes in gene expression and physiology (Guilfoyle and Hagen, 2007), and the down-regulation of auxin synthesis and signaling can be considered a primary event in the progression of senescence. Although reports of the role of auxin in leaf senescence conflict (Quirino et al, 1999;Okushima et al, 2005;Hou et al, 2013;Jiang et al, 2014), our molecular data suggest that auxin action is down-regulated during the progression of leaf senescence.…”

Networks controlling seed size in Arabidopsis

“…ARF genes take part in auxin-related 361 responses and recognize specific AuxRE (auxin response 362 elements) consensus elements on target genes (Ulmasov 363 et al 1999). Among the different ARF proteins, ARF2 is 364 thought to act as a transcriptional repressor, exercising a 365 negative control over cell proliferation and expansion (Li 366 et al 2004;Okushima et al 2005;Schruff et al 2006). In 367 particular, different arf2 loss-of-function mutants exhibit 368 abnormal flower morphology and enlarged seeds in com-369 parison with the wild type (Okushima et al 2005), a phe-370 notype characterized in detail in the case of arf2-9, which 371 presented more cells in the seed coat compared with wild-372 type seeds.…”

“…Among the different ARF proteins, ARF2 is 364 thought to act as a transcriptional repressor, exercising a 365 negative control over cell proliferation and expansion (Li 366 et al 2004;Okushima et al 2005;Schruff et al 2006). In 367 particular, different arf2 loss-of-function mutants exhibit 368 abnormal flower morphology and enlarged seeds in com-369 parison with the wild type (Okushima et al 2005), a phe-370 notype characterized in detail in the case of arf2-9, which 371 presented more cells in the seed coat compared with wild-372 type seeds. The result of the increased volume of the seed 373 cavity in arf2-9 is that seeds are 46 % heavier than the 374 wild-type seeds, showing in some cases additional cell 375 layers in the seed coat (Schruff et al 2006).…”

Plant fertility defects induced by the enhanced expression of microRNA167

“…ARF proteins are known to act upstream of many physiological effects of auxin. Although a few ARF genes have been characterized functionally [21,22,[25][26][27][28][29], the functions for many other ARFs remain unknown. Recent studies indicate that the several ARF genes are negatively regulated via small RNAs at the post-transcriptional level.…”