Storage compound accumulation during seed development prepares the next generation of plants for survival. Therefore, processes involved in the regulation and synthesis of storage compound accumulation during seed development bear relevance to germination and seedling establishment. The wrinkled1 (wri1) mutant of Arabidopsis (Arabidopsis thaliana) is impaired in seed oil accumulation. The WRI1 gene encodes an APETALA2/ethylene-responsive element-binding protein transcription factor involved in the control of metabolism, particularly glycolysis, in the developing seeds. Here we investigate the role of this regulatory factor in seed germination and seedling establishment by comparing the wri1-1 mutant, transgenic lines expressing the WRI1 wild-type cDNA in the wri1-1 mutant background, and the wild type. Plants altered in the expression of the WRI1 gene showed different germination responses to the growth factor abscisic acid (ABA), sugars, and fatty acids provided in the medium. Germination of the mutant was more sensitive to ABA, sugars, and osmolites, an effect that was alleviated by increased WRI1 expression in transgenic lines. The expression of ABA-responsive genes AtEM6 and ABA-insensitive 3 (ABI3) was increased in the wri1-1 mutant. Double-mutant analysis between abi3-3 and wri1-1 suggested that WRI1 and ABI3, a transcription factor mediating ABA responses in seeds, act in parallel pathways. Addition of 2-deoxyglucose inhibited seed germination, but did so less in lines overexpressing WRI1. Seedling establishment was decreased in the wri1-1 mutant but could be alleviated by sucrose. Apart from a possible signaling role in germination, sugars in the medium were required as building blocks and energy supply during wri1-1 seedling establishment.

Nucleocytoplasmic transport of macromolecules is regulated by a large multisubunit complex called the nuclear pore complex (NPC). Although this complex is well characterized in animals and fungi, there is relatively little information on the NPC in plants. The suppressor of auxin resistance1 (sar1) and sar3 mutants were identified as suppressors of the auxin-resistant1 (axr1) mutant. Molecular characterization of these genes reveals that they encode proteins with similarity to vertebrate nucleoporins, subunits of the NPC. Furthermore, a SAR3-green fluorescent protein fusion protein localizes to the nuclear membrane, indicating that SAR1 and SAR3 are Arabidopsis thaliana nucleoporins. Plants deficient in either protein exhibit pleiotropic growth defects that are further accentuated in sar1 sar3 double mutants. Both sar1 and sar3 mutations affect the localization of the transcriptional repressor AXR3/INDOLE ACETIC ACID17, providing a likely explanation for suppression of the phenotype conferred by axr1. In addition, sar1 sar3 plants accumulate polyadenylated RNA within the nucleus, indicating that SAR1 and SAR3 are required for mRNA export. Our results demonstrate the important role of the plant NPC in hormone signaling and development.

The accumulation of storage compounds during seed development ensures the survival of the young seedling, and also provides nutrition to humans and animals in the form of foods and feeds. The putative AP2/EREBP transcription factor WRINKLED1 (WRI1) is involved in the regulation of seed storage metabolism in Arabidopsis. A splicing mutant allele, wri1-1, caused the reduction of seed oil accumulation. Glycolysis was compromised in this mutant, rendering developing embryos unable to efficiently convert sucrose into precursors of triacylglycerol biosynthesis. Expression of the WRINKLED1 cDNA under the control of the cauliflower mosaic virus 35S-promoter led to increased seed oil content. Moreover, the ectopic expression of the WRINKLED1 cDNA caused the accumulation of triacylglycerols in developing seedlings. This effect depended upon the presence of glucose in the growth medium or other sugars readily metabolized to glucose. Oil-accumulating seedlings showed aberrant development consistent with a prolonged embryonic state.

Genetic and physiological studies implicate the phytohormones auxin and ethylene in root hair development. To learn more about the role of these compounds, we have examined the root hair phenotype of a number of auxin- and ethylene-related mutants. In a previous study, Masucci and Schiefelbein (1996) showed that neither the auxin response mutations aux1 and axr1 nor the ethylene response mutations etr1 and ein2 have a significant effect on root hair initiation. In this study, we found that mutants deficient in either auxin or ethylene response have a pronounced effect on root hair length. Treatment of wild-type, axr1 and etr1 seedlings with the synthetic auxin, 2,4-D, or the ethylene precursor ACC, led to the development of longer root hairs than untreated seedlings. Furthermore, axr1 seedlings grown in the presence of ACC produce ectopic root hairs and an unusual pattern of long root hairs followed by regions that completely lack root hairs. These studies indicate that both auxin and ethylene are required for normal root hair elongation.

A screen for suppressors of the auxin resistant mutant axr1 in Arabidopsis thaliana has identified at least three second site suppressor loci called Suppressor of Auxin Resistance (SAR). In this study we focus on the SAR1 gene. Previous studies have documented the effects of the axr1 mutations on auxin-inhibition of root growth, auxin-induced gene expression, seedling morphology and aerial morphology. In this study, we show that the axr1 mutations also affect root hair development and epidermal cell length. The sar1-1 mutation suppresses at least partially, every aspect of the axr1 phenotype. Genetic experiments indicate that this suppression is gene specific. When crossed with the auxinresistant mutant aux1-7 , the suppressor has little affect on auxin response. However, the morphology of sar1-1 aux1-7 inflorescences is different from either of the single mutants indicating that both genes play a role in auxin mediated development of the inflorescence. The sar1-1 mutation also affects morphology in an AXR1 background. sar1-1 plants are shorter than wild-type, have altered leaf morphology, flower earlier than wild-type plants and appear to have reduced cell division in the primary root. In most respects sar1-1 axr1 and sar1 AXR1 plants are indistinguishable, indicating that sar1 both suppresses and is epistatic to axr1. Based on these results, we propose that SAR1 acts after AXR1 and that a major function of AXR1 is to relieve SAR1 mediated repression of auxin response.

A screen for suppressors of the auxin resistant mutant axr1 in Arabidopsis thaliana has identified at least three second site suppressor loci called Suppressor of Auxin Resistance (SAR). In this study we focus on the SAR1 gene. Previous studies have documented the effects of the axr1 mutations on auxin-inhibition of root growth, auxin-induced gene expression, seedling morphology and aerial morphology. In this study, we show that the axr1 mutations also affect root hair development and epidermal cell length. The sar1-1 mutation suppresses at least partially, every aspect of the axr1 phenotype. Genetic experiments indicate that this suppression is gene specific. When crossed with the auxin-resistant mutant aux1-7, the suppressor has little affect on auxin response. However, the morphology of sar1-1 aux1-7 inflorescences is different from either of the single mutants indicating that both genes play a role in auxin mediated development of the inflorescence. The sar1-1 mutation also affects morphology in an AXR1 background. sar1-1 plants are shorter than wild-type, have altered leaf morphology, flower earlier than wild-type plants and appear to have reduced cell division in the primary root. In most respects sar1-1 axr1 and sar1 AXR1 plants are indistinguishable, indicating that sar1 both suppresses and is epistatic to axr1. Based on these results, we propose that SAR1 acts after AXR1 and that a major function of AXR1 is to relieve SAR1 mediated repression of auxin response.