The Arabidopsis thaliana AtOPT3 belongs to the oligopeptide transporter (OPT) family, a relatively poorly characterized family of peptide/modified peptide transporters found in archebacteria, bacteria, fungi, and plants. A null mutation in AtOPT3 resulted in embryo lethality, indicating an essential role for AtOPT3 in embryo development. In this article, we report on the isolation and phenotypic characterization of a second AtOPT3 mutant line, opt3-2, harboring a T-DNA insertion in the 5# untranslated region of AtOPT3. The T-DNA insertion in the AtOPT3 promoter resulted in reduced but sufficient AtOPT3 expression to allow embryo formation in opt3-2 homozygous seeds. Phenotypic analyses of opt3-2 plants revealed three interesting loss-of-function phenotypes associated with iron metabolism. First, reduced AtOPT3 expression in opt3-2 plants resulted in the constitutive expression of root iron deficiency responses regardless of exogenous iron supply. Second, deregulation of root iron uptake processes in opt3-2 roots resulted in the accumulation of very high levels of iron in opt3-2 tissues. Hyperaccumulation of iron in opt3-2 resulted in the formation of brown necrotic areas in opt3-2 leaves and was more pronounced during the seed-filling stage. Third, reduced AtOPT3 expression resulted in decreased accumulation of iron in opt3-2 seeds. The reduced accumulation of iron in opt3-2 seeds is especially noteworthy considering the excessively high levels of accumulated iron in other opt3-2 tissues. AtOPT3, therefore, plays a critical role in two important aspects of iron metabolism, namely, maintenance of whole-plant iron homeostasis and iron nutrition of developing seeds.
SUMMARYLong-distance communication between leaves and roots are key to properly regulate the uptake of trace metals from the soil. The molecular basis of this shoot-to-root signaling is currently unknown. In this manuscript, we describe the role of OPT3 in the shoot-to-root signaling of the iron status in Arabidopsis. We also show that reduced expression of OPT3 induces an over-accumulation of the toxic metal cadmium, but not other metals, in seeds.
AtOPT promoter-GUS fusions were constructed for six of the nine known, putative oligopeptide transporters (OPTs) in Arabidopsis thaliana and used to examine AtOPT expression at various stages of plant development. AtOPT1, AtOPT3, AtOPT4, AtOPT6 and AtOPT7 were expressed in the embryonic cotyledons prior to root radicle emergence. Except for AtOPT8, which gave weak expression, all AtOPTs were strongly expressed in post-germinative seedlings with strongest expression in vascular tissues of cotyledons and hypocotyls. Preferential expression of AtOPTs in vascular tissues was also observed in cotyledons, leaves, hypocotyls, roots, flowers, siliques, and seed funiculi of seedlings and adult plants. Differential tissue-specific expression was observed for specific AtOPTs. For example, AtOPT1, AtOPT3 and AtOPT8 were uniquely expressed in pollen. Only AtOPT1 was expressed in growing pollen tubes, while only AtOPT6 was observed in ovules. AtOPT8 was transiently expressed in seeds during early stages of embryogenesis. Iron limitation was found to enhance expression of AtOPT3. These data suggest distinct cellular roles for specific AtOPTs including nitrogen mobilization during germination and senescence, pollen tube growth, pollen and ovule development, seed formation and metal transport.
Lectin receptor-like kinases (Lectin RLKs) are a large family of receptor-like kinases with an extracellular legume lectin-like domain. There are approximately 45 such receptor kinases in Arabidopsis thaliana. Surprisingly, although receptor-like kinases in general are well investigated in Arabidopsis, relatively little is known about the functions of members of the Lectin RLK family. A number of studies implicated members of this family in various functions, such as disease resistance, stress responses, hormone signaling, and legume-rhizobium symbiosis. Our current work demonstrated that mutation in one Lectin RLK gene led to male sterility in Arabidopsis. The sterility was due to defects in pollen development. Pollen development proceeded normally in the mutant until anther stage 8. After that, all pollen grains deformed and collapsed. Mature pollen grains were much smaller than wild-type pollen grains, glued together, and totally collapsed. Therefore, the mutant was named sgc, standing for small, glued-together, and collapsed pollen mutant. The mutant phenotype appeared to be caused by an unidentified sporophytic defect due to the mutation. As revealed by analysis of the promoter-GUS transgenic plants and the gene expression analysis using RT-PCR, the gene showed an interesting temporal and spatial expression pattern: it had no or a low expression in young flowers (roughly before anther stage 6), reached a maximum level around stages 6-7, and then declined gradually to a very low level in young siliques. No expression was detected in microspores or pollen. Together, our data demonstrated that SGC Lectin RLK plays a critical role in pollen development.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.