pho2, a Phosphate Overaccumulator, Is Caused by a Nonsense Mutation in a MicroRNA399 Target Gene

Institute of BioAgricultural Sciences , Academia Sinica, Taipei 115, Taiwan, Republic of China.
Plant physiology (Impact Factor: 6.84). 08/2006; 141(3):1000-11. DOI: 10.1104/pp.106.078063
Source: PubMed


We recently demonstrated that microRNA399 (miR399) controls inorganic phosphate (Pi) homeostasis by regulating the expression of UBC24 encoding a ubiquitin-conjugating E2 enzyme in Arabidopsis (Arabidopsis thaliana). Transgenic plants overexpressing miR399 accumulated excessive Pi in the shoots and displayed Pi toxic symptoms. In this study, we revealed that a previously identified Pi overaccumulator, pho2, is caused by a single nucleotide mutation resulting in early termination within the UBC24 gene. The level of full-length UBC24 mRNA was reduced and no UBC24 protein was detected in the pho2 mutant, whereas up-regulation of miR399 by Pi deficiency was not affected. Several characteristics of Pi toxicity in the pho2 mutant were similar to those in the miR399-overexpressing and UBC24 T-DNA knockout plants: both Pi uptake and translocation of Pi from roots to shoots increased and Pi remobilization within leaves was impaired. These phenotypes of the pho2 mutation could be rescued by introduction of a wild-type copy of UBC24. Kinetic analyses revealed that greater Pi uptake in the pho2 and miR399-overexpressing plants is due to increased Vmax. The transcript level of most PHT1 Pi transporter genes was not significantly altered, except PHT1;8 whose expression was enhanced in Pi-sufficient roots of pho2 and miR399-overexpressing compared with wild-type plants. In addition, changes in the expression of several organelle-specific Pi transporters were noticed, which may be associated with the redistribution of intracellular Pi under excess Pi. Furthermore, miR399 and UBC24 were colocalized in the vascular cylinder. This observation not only provides important insight into the interaction between miR399 and UBC24 mRNA, but also supports their systemic function in Pi translocation and remobilization.

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Available from: Kyaw Aung, Aug 31, 2014
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    • "The complex network of regulatory genes necessary to sense and respond to Pi deficiency is being dissected (Smith et al., 2010; Yang and Finnegan, 2010; Hammond and White, 2011; Kuo and Chiou, 2011). For example, in Arabidopsis thaliana, a major transcriptional regulatory system that involves PHR1, SIZ1, miR399 and PHO2 in response to Pi deficiency has been identified (Rubio et al., 2001; Fujii et al., 2005; Aung et al., 2006; Schachtman and Shin, 2007). In contrast to Arabidopsis, recent studies have shown that the PHR1-miR399-PHO2 signalling pathway also operates in rice plants in response to Pi deficiency. "
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    ABSTRACT: The WRKY transcription factor family has 109 members in the rice genome, and has been reported to be involved in the regulation of biotic and abiotic stress in plants. Here, we demonstrated that a rice OsWRKY74 belonging to group III of the WRKY transcription factor family was involved in tolerance to phosphate (Pi) starvation. OsWRKY74 was localized in the nucleus and mainly expressed in roots and leaves. Overexpression of OsWRKY74 significantly enhanced tolerance to Pi starvation, whereas transgenic lines with down-regulation of OsWRKY74 were sensitive to Pi starvation. Root and shoot biomass, and phosphorus (P) concentration in rice OsWRKY74-overexpressing plants were ~16% higher than those of wild-type (WT) plants in Pi-deficient hydroponic solution. In soil pot experiments, >24% increases in tiller number, grain weight and P concentration were observed in rice OsWRKY74-overexpressing plants compared to WT plants when grown in P-deficient medium. Furthermore, Pi starvation-induced changes in root system architecture were more profound in OsWRKY74-overexpressing plants than in WT plants. Expression patterns of a number of Pi-responsive genes were altered in the OsWRKY74-overexpressing and RNA interference lines. In addition, OsWRKY74 may also be involved in the response to deficiencies in iron (Fe) and nitrogen (N) as well as cold stress in rice. In Pi-deficient conditions, OsWRKY74-overexpressing plants exhibited greater accumulation of Fe and up-regulation of the cold-responsive genes than WT plants. These findings highlight the role of OsWRKY74 in modulation of Pi homeostasis and potential crosstalk between P starvation and Fe starvation, and cold stress in rice.
    Preview · Article · Dec 2015 · Journal of Experimental Botany
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    • "been demonstrated to regulate Pi homeostasis in Arabidopsis by binding to the 5′-UTR of PHO2 (a gene encoding ubiquitin-conjugating E2) (Aung et al. 2006, Bari et al. 2006, Chiou et al. 2006, Fujii et al. 2005). There are six members of the miR399 family have been identified in Arabidopsis, 11 in rice, and 10 in maize (Sunkar and Zhu 2004, Zhang et al. 2009). "
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    ABSTRACT: Phosphorus (P) is an essential element involved in numerous biochemical reactions. In plants, stress responses, such as the expression of microRNAs (miRNAs), are induced to help them adapt to low phosphate (Pi) concentrations. In this study, deep sequencing was performed using the roots and leaves of maize seedlings grown under low Pi concentrations to identify miRNAs that are differentially expressed during the early stages of Pi deficiency. Eight small RNA libraries were constructed, and 159 known miRNAs representing 32 miRNA families and 10 novel miRNAs. Members of the miR396 family were extremely abundant. Further, 28 Pi-responsive miRNAs were identified (27 known and 1 novel) of which 8 and 7 were significantly expressed exclusively in leaf and root tissues, respectively. The analysis of Pi-responsive miRNAs target genes suggested that most target genes functioning as transcription factors were involved in root and leaf development. The expression profiles of selected Pi-responsive miRNAs and target genes were confirmed by qRT-PCR. Moreover, we discuss the significance of the differences in expression patterns of these miRNAs during the early and later stages of Pi starvation. The present study provides useful information concerning the role of miRNAs in response to Pi starvation and will further our understanding of the mechanisms governing Pi homeostasis in maize.
    Full-text · Article · Nov 2015 · Physiologia Plantarum
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    • "Pi deficiency deeply affects plant growth, development, and metabolism (Ticconi and Abel, 2004). pho2 is a Pi-overaccumulator mutant with enhanced uptake and root-to-root translocation of Pi. pho2 is defective in UBC24, which encodes a putative E2 enzyme (Aung et al., 2006; Bari et al., 2006). In Pi deficiency conditions, the transcription factor PHR1 upregulates miR399, which targets the 5 UTR of PHO2 for cleavage. "
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    ABSTRACT: Ubiquitination is a major modifier of signaling in all eukaryotes that results in the conjugation of ubiquitin to the lysine residues of acceptor proteins. The targeted protein is then subjected to degradation by the 26S proteasome, the major protein degradation system in eukaryotes. The ubiquitin–proteasome system (UPS) greatly influences plant growth and development by modulating the activity, localization, and stability of proteins. Plants are frequently exposed to various abiotic stresses during their life cycles; they rely on proteomic plasticity achieved by the UPS to adapt to unfavorable environmental conditions. In stress signal pathways, a large number of components are modified by specific ubiquitination machinery. In this review, we highlight recent advances in understanding the roles of ubiquitination in plant responses to abiotic stresses, including salt and drought, temperature, ultraviolet (UV), and nutrient availability. The review focuses primarily on the roles of the UPS. In salt and/or drought stress signaling, a number of E3 ligases mediate the stress response in both abscisic acid (ABA)-dependent and ABA-independant pathways. The UPS-mediated regulation of several key ABA-regulated transcriptional factors, e.g. ABI3 and ABI5, has been well documented. In cold signaling, the transcription factor ICE1 is targeted by E3 ligase HOSI for proteosomal degradation. Under UV stress, CUL4-DDB1A-DDB2 E3 ligase participates in DNA excision repair, and COP1 interacts with the UVR8 mediated UV response. The UPS is also involved in the uptake, transport, and homeostasis of nutrients such as iron, phosphorus, and nitrogen. SIZ1-mediated sumoylation, a ubiquitin-like modification, is necessary for a number of processes involved in plant responses to abiotic stresses. A challenge moving forward for researchers is to define more UPS components and to characterize their functions in plant responses to stress conditions; there is particular interest in identifying the ubiquitination targets that function in specific stress signaling pathways.
    Preview · Article · Jun 2015 · Environmental and Experimental Botany
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