SummaryOf the mineral nutrients essential for plant growth, phosphorus plays the widest diversity of roles and a lack of phosphorus has profound effects on cellular metabolism. At least eight members of the Arabidopsis Pht1 phosphate (Pi) transporter family are expressed in roots and Pht1;1 and Pht1;4 show the highest transcript levels. The spatial and temporal expression patterns of these two genes show extensive overlap. To elucidate the in planta roles of Pht1;1 and Pht1;4, we identified loss-of-function mutants and also created a double mutant, lacking both Pht1;1 and Pht1;4. Consistent with their spatial expression patterns, membrane location and designation as high-affinity Pi transporters, Pht1;1 and Pht1;4 contribute to Pi transport in roots during growth under low-Pi conditions. In addition, during growth under high-Pi conditions, the double mutant shows a 75% reduction in Pi uptake capacity relative to wildtype. Thus, Pht1;1 and Pht1;4 play significant roles in Pi acquisition from both low-and high-Pi environments.

SummaryPlants display a range of adaptive responses to phosphate (Pi) starvation including an increase in the proportion of Pi allocated to the roots, which enhances lateral root development and consequently Pi acquisition. The mechanisms by which plants sense Pi and signal Pi reallocation are largely unknown. Previously, we cloned At4, a gene predicted to contain multiple short open-reading frames (ORFs), whose expression is strongly induced by Pi starvation. At4 is a member of a small gene family whose members, AtIPS1 and two additional genes reported here, At4.1 and At4.2, share little conservation among the predicted ORFs but high conservation of a 22-nt sequence located in the 3¢ half of the transcript. Here, we show that under Pi-starvation conditions, At4 is expressed in the vascular tissue and transcript levels are regulated by both cytokinin and ABA. at4, an At4 loss-of-function mutant fails to redistribute Pi to the roots correctly in response to Pi deprivation and At4 shoots continue to accumulate a greater proportion of Pi relative to wild type. Consistent with this, the primary root growth rate in at4 is faster than wild type in low-Pi conditions. The conserved sequence found in all members of the At4 gene family hybridizes to a small RNA present in Pistarved roots. These data support a role for At4 in the internal allocation of Pi and suggest that the At4 gene is not only subject to Pi-starvation-inducible expression, but that transcript levels may be adjusted at a posttranscriptional level by the activity of an miRNA.

SummaryPolar auxin transport, mediated by two distinct plasma membrane-localized auxin influx and efflux carrier proteins/complexes, plays an important role in many plant growth and developmental processes including tropic responses to gravity and light, development of lateral roots and patterning in embryogenesis. We have previously shown that the Arabidopsis AGRAVITROPIC 1/PIN2 gene encodes an auxin efflux component regulating root gravitropism and basipetal auxin transport. However, the regulatory mechanism underlying the function of AGR1/PIN2 is largely unknown. Recently, protein phosphorylation and dephosphorylation mediated by protein kinases and phosphatases, respectively, have been implicated in regulating polar auxin transport and root gravitropism. Here, we examined the effects of chemical inhibitors of protein phosphatases on root gravitropism and basipetal auxin transport, as well as the expression pattern of AGR1/PIN2 gene and the localization of AGR1/PIN2 protein. We also examined the effects of inhibitors of vesicle trafficking and protein kinases. Our data suggest that protein phosphatases, sensitive to cantharidin and okadaic acid, are likely involved in regulating AGR1/PIN2-mediated root basipetal auxin transport and gravitropism, as well as auxin response in the root central elongation zone (CEZ). BFA-sensitive vesicle trafficking may be required for the cycling of AGR1/PIN2 between plasma membrane and the BFA compartment, but not for the AGR1/PIN2-mediated root basipetal auxin transport and auxin response in CEZ cells.

The serum lipid metabolites of lean and obese mice fed normal or high-fat diets were analyzed via direct infusion nanoelectrospray-ion trap mass spectrometry followed by multivariate analysis. In addition, lipidomic biomarkers responsible for the pharmacological effects of compound K-reinforced ginsenosides (CK), thus the CK fraction, were evaluated in mice fed high-fat diets. The obese and lean groups were clearly discriminated upon principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) score plot, and the major metabolites contributing to such discrimination were triglycerides (TGs), cholesteryl esters (CEs), phosphatidylcholines (PCs), and lysophosphatidylcholines (LPCs). TGs with high total carbon number (>50) and low total carbon number (<50) were negatively and positively associated with high-fat diet induced obesity in mice, respectively. When the CK fraction was fed to obese mice that consumed a high-fat diet, the levels of certain lipids including LPCs and CEs became similar to those of mice fed a normal diet. Such metabolic markers can be used to better understand obesity and related diseases induced by a hyperlipidic diet. Furthermore, changes in the levels of such metabolites can be employed to assess the risk of obesity and the therapeutic effects of obesity management.

The Arabidopsis A1-type cyclin, CYCA1;2, also named TARDY ASYNCHRONOUS MEIOSIS (TAM), is known for its positive role in meiotic cell cycle progression, but its function in other cells has not been characterized. This paper reports the role of CYCA1;2/TAM in differentiated cells in vegetative organs. The pattern of CYCA1;2/TAM expression was investigated by promoter and protein fusions using the β-glucuronidase and the green fluorescent protein, respectively. The relevance of the promoter region used in these gene fusion constructs was verified by the effective complementation of the phenotype of the diploid null allele, tam-2 2C by a genomic fragment containing the wild-type coding region of CYCA1;2/TAM and the promoter region. CYCA1;2/TAM expression was found primarily in non-proliferating cells such as guard cells, trichomes, and mesophyll cells, and in vascular tissue. In two types of overexpression lines, one containing the CYCA1;2/TAM transgene driven by the ARABIDOPSIS SKP1-LIKE1 (ASK1) promoter and the other CYCA1;2/TAM-GFP driven by the cauliflower mosaic virus 35S promoter, the largest differences between the transgene transcript levels were approximately 72- and 45-folds, respectively, but the TAM-GFP signal levels in the mesophyll and stomata in the 35S:TAM-GFP lines only differ slightly. Furthermore, the GFP signals in the mesophyll and stomata in the TAM:TAM-GFP and 35S:TAM-GFP lines were all at similarly low levels. These results indicate that the CYCA1;2/TAM protein is likely maintained at low levels in these cells through post-transcriptional regulation. Loss of function in CYCA1;2/TAM resulted in increases in the nuclear size in both trichomes and guard cells. Surprisingly, overexpression of CYCA1;2/TAM led to similar increases. The large increases in trichome nuclear size likely reflected ploidy increases while the moderate increases in guard cell nuclear size did not justify for a ploidy increase. These nuclear size increases were not clearly correlated with trichome branch number increases and guard cell size increases, respectively. These results suggest that cellular homeostasis of the CYCA1;2/TAM protein is linked to the control of nuclear sizes in trichomes and guard cells.