The screening of the Versailles collection of Arabidopsis T-DNA transformants allowed us to identify several male gametophytic mutants, including poky pollen tube (pok). The pok mutant, which could only be isolated as a hemizygous line, exhibits very short pollen tubes, explaining the male-specific transmission defect observed in this line. We show that the POK gene is duplicated in the Arabidopsis genome and that the predicted POK protein sequence is highly conserved from lower to higher eukaryotes. The putative POK homolog in yeast (Saccharomyces cerevisiae), referred to as Vps52p/SAC2, has been shown to be located at the late Golgi and to function in a complex with other proteins, Vps53p, Vps54p, and Vps51p. This complex is involved in retrograde trafficking of vesicles between the early endosomal compartment and the trans-Golgi network. We present the expression patterns of the POK gene and its duplicate P2 in Arabidopsis, and of the putative Arabidopsis homologs of VPS53 and VPS54 of yeast. We show that a POK::GFP fusion protein localizes to Golgi in plant cells, supporting the possibility of a conserved function for Vps52p and POK proteins. These results, together with the expression pattern of the POK::GUS fusion and the lack of plants homozygous for the pok mutation, suggest a more general role for POK in polar growth beyond the pollen tube elongation process.Pollen tube growth is a vital process during male gametophyte development, since it allows male gametes to reach the ovules and achieve fertilization (Preuss, 1995). The elongation of the pollen tube, as well as that of animal axons, plant root hairs, fungal hyphae, and moss protonema, is achieved by a polarized mode of growth, termed tip growth (FranklinTong, 1999;Palanivelu and Preuss, 2000;Hepler et al., 2001), which involves the tip-localized exocytosis of Golgi-derived vesicles containing cell wall precursors (Franklin-Tong, 1999). The tip of the pollen tube is devoid of organelles, but contains almost exclusively Golgi-derived vesicles (Geitmann and Emons, 2000). In the shank of the tubes, an inverse fountain pattern of cytoplasmic streaming is observed; organelles and vesicles are transported toward the apex in the cortical region and basipetally in the central cytoplasm (Pierson et al., 1990). Actin filaments and microtubules, which are organized in longitudinal arrays more or less parallel to the elongation axis, act as tracks for cytoplasmic streaming and allow delivery of vesicles to the tip (Pierson et al., 1990;Vidali and Hepler, 2001). The use of membrane structure dyes, such as FM1-43 or FM4-64 (Parton et al., 2001;Camacho and Malhó , 2003), has revealed dynamic endo/ exocytosis processes at the tip of the pollen tube, but the molecular events underlying these processes are still poorly understood. The recent identification of the Golgi-associated tobacco (Nicotiana tabacum), Rab GTPase NtRab2, predominantly expressed in pollen, suggests that tip growth and vesicle trafficking could be tightly linked (Cheung et al., 2002). Moreover, a...
Transcriptional regulation of the tobacco retrotransposon Tnt1 was monitored in Arabidopsis thaliana and Lycopersicon esculentum. In these two heterologous host species, Tnt1 expression is developmentally regulated, and its tissue‐specific pattern of transcription is similar to that observed in tobacco, with the exception that Tnt1 is expressed in their flowers. Induction of Tnt1 by microbial elicitors, previously found in tobacco, is maintained in Arabidopsis and tomato. Tnt1 activation is not strictly dependent upon a Hypersensitive Response‐like necrotic response, but also occurs in a plant‐pathogen compatible interaction triggered by viral or bacterial infections. The putative role of Tnt1 in generating genetic variability in its host plant is discussed.
Many genes are thought to be expressed during the haploid phase in plants, however, very few haploid-specific genes have been isolated so far. T-DNA insertion mutagenesis is a powerful tool for generating mutations that affect gametophyte viability and function, as disruption of a gene essential for these processes should lead to a defect in the transmission of the gametes. Mutants can therefore be screened on the basis of segregation distortion for a reporter resistance gene contained in the T-DNA. We have screened the Versailles collection of Arabidopsis transformants for 1:1 KanR:KanS segregation after selfing, focussing on gametophyte mutations which show normal transmission through one gametophyte and cause lethality or dysfunction of the other. Only 1.3% (207) of the 16,000 lines screened were scored as good candidates. Thorough genetic analysis of 38 putative T-DNA transmission defect lines (Ttd) identified 8 defective gametophyte mutants, which all showed 0 to 1% T-DNA transmission through the pollen. During the screen, we observed a high background of low-penetrance mutations, often affecting the function of both gametophytes, and many lines which were likely to carry chromosomal rearrangements. The reasons for the small number of retained lines (all male gametophytic) are discussed, as well as the finding that, for most of them, residual T-DNA transmission is obtained through the affected gametophyte.
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.