Jeffery L. Gustin

MTP1-dependent Zn sequestration into shoot vacuoles suggests dual roles in Zn tolerance and accumulation in Zn-hyperaccumulating plants.

The integral membrane protein Thlaspi goesingense metal tolerance protein 1 (TgMTP1) has been suggested to play an important role in Zn hyperaccumulation in T. goesingense. Here, we show that the TgMTP1 protein is accumulated to high levels at the vacuolar membrane in shoot tissue of T. goesingense. TgMTP1 is likely to act in the transport of Zn into the vacuole, enhancing both Zn accumulation and tolerance. By specifically expressing TgMTP1 in Arabidopsis thaliana shoots, we show that TgMTP1, localized at the vacuolar membrane, can drive the enhanced shoot accumulation of Zn by initiating a systemic Zn deficiency response. The systematic response includes increased expression of Zn transporters (ZIP3, ZIP4, ZIP5 and ZIP9) in both shoot and root tissue. Furthermore, shoot-specific accumulation of TgMTP1 at the vacuolar membrane also leads to increased resistance to Zn in A. thaliana, probably through enhanced Zn compartmentalization in the vacuole. Such evidence leads to the conclusion that the high levels of TgMTP1 at the vacuolar membrane in shoot tissue of the Zn hyperaccumulator T. goesingense play a role in both Zn tolerance and enhanced Zn uptake and accumulation, via the activation of a systemic Zn deficiency response.

Structure and evolution of the plant cation diffusion facilitator family of ion transporters.

BackgroundMembers of the cation diffusion facilitator (CDF) family are integral membrane divalent cation transporters that transport metal ions out of the cytoplasm either into the extracellular space or into internal compartments such as the vacuole. The spectrum of cations known to be transported by proteins of the CDF family include Zn, Fe, Co, Cd, and Mn. Members of this family have been identified in prokaryotes, eukaryotes, and archaea, and in sequenced plant genomes. CDF families range in size from nine members in Selaginella moellendorffii to 19 members in Populus trichocarpa. Phylogenetic analysis suggests that the CDF family has expanded within plants, but a definitive plant CDF family phylogeny has not been constructed.ResultsRepresentative CDF members were annotated from diverse genomes across the Viridiplantae and Rhodophyta lineages and used to identify phylogenetic relationships within the CDF family. Bayesian phylogenetic analysis of CDF amino acid sequence data supports organizing land plant CDF family sequences into 7 groups. The origin of the 7 groups predates the emergence of land plants. Among these, 5 of the 7 groups are likely to have originated at the base of the tree of life, and 2 of 7 groups appear to be derived from a duplication event prior to or coincident with land plant evolution. Within land plants, local expansion continues within select groups, while several groups are strictly maintained as one gene copy per genome.ConclusionsDefining the CDF gene family phylogeny contributes to our understanding of this family in several ways. First, when embarking upon functional studies of the members, defining primary groups improves the predictive power of functional assignment of orthologous/paralogous genes and aids in hypothesis generation. Second, defining groups will allow a group-specific sequence motif to be generated that will help define future CDF family sequences and aid in functional motif identification, which currently is lacking for this family in plants. Third, the plant-specific expansion resulting in Groups 8 and 9 evolved coincident to the early primary radiation of plants onto land, suggesting these families may have been important for early land colonization.

Reciprocal grafting separates the roles of the root and shoot in zinc hyperaccumulation in Thlaspi caerulescens

The extreme phenotype of zinc (Zn) hyperaccumulation, which is found in several Brassicaceae species, is determined by mechanisms that promote elevated Zn tolerance and high Zn accumulation in shoots. We used reciprocal grafting between a Zn hyperaccumulator, Thlaspi caerulescens, and a Zn nonaccumulator, Thlaspi perfoliatum, to determine the relative importance of roots and shoots in Zn hyperaccumulation and hypertolerance. Leaves from plants with a T. perfoliatum rootstock and a T. caerulescens shoot scion did not hyperaccumulate Zn, whereas plants with a T. caerulescens rootstock and a T. perfoliatum shoot scion did hyperaccumulate Zn. However, although leaves from plants with a T. caerulescens rootstock and a T. perfoliatum shoot scion hyperaccumulated Zn, at high Zn loads these leaves showed significant symptoms of Zn toxicity, unlike leaves of self grafted T. caerulescens. Hyperaccumulation of Zn in leaves of the hyperaccumulator T. caerulescens is pri-marily dictated by root processes. Further, the mechanisms controlling Zn hypertolerance in the hyperaccumulator T. caerulescens are driven primarily by shoot processes.

Analysis of maize ( Zea mays ) kernel density and volume using microcomputed tomography and single-kernel near-infrared spectroscopy.

Maize kernel density affects milling quality of the grain. Kernel density of bulk samples can be predicted by near-infrared reflectance (NIR) spectroscopy, but no accurate method to measure individual kernel density has been reported. This study demonstrates that individual kernel density and volume are accurately measured using X-ray microcomputed tomography (μCT). Kernel density was significantly correlated with kernel volume, air space within the kernel, and protein content. Embryo density and volume did not influence overall kernel density. Partial least-squares (PLS) regression of μCT traits with single-kernel NIR spectra gave stable predictive models for kernel density (R(2) = 0.78, SEP = 0.034 g/cm(3)) and volume (R(2) = 0.86, SEP = 2.88 cm(3)). Density and volume predictions were accurate for data collected over 10 months based on kernel weights calculated from predicted density and volume (R(2) = 0.83, SEP = 24.78 mg). Kernel density was significantly correlated with bulk test weight (r = 0.80), suggesting that selection of dense kernels can translate to improved agronomic performance.

Enhanced Single Seed Trait Predictions in Soybean (Glycine max) and Robust Calibration Model Transfer with Near-Infrared Reflectance Spectroscopy

Single seed near-infrared reflectance (NIR) spectroscopy predicts soybean (Glycine max) seed quality traits of moisture, oil, and protein. We tested the accuracy of transferring calibrations between different single seed NIR analyzers of the same design by collecting NIR spectra and analytical trait data for globally diverse soybean germplasm. X-ray microcomputed tomography (μCT) was used to collect seed density and shape traits to enhance the number of soybean traits that can be predicted from single seed NIR. Partial least-squares (PLS) regression gave accurate predictive models for oil, weight, volume, protein, and maximal cross-sectional area of the seed. PLS models for width, length, and density were not predictive. Although principal component analysis (PCA) of the NIR spectra showed that black seed coat color had significant signal, excluding black seeds from the calibrations did not impact model accuracies. Calibrations for oil and protein developed in this study as well as earlier calibrations for a separate NIR analyzer of the same design were used to test the ability to transfer PLS regressions between platforms. PLS models built from data collected on one NIR analyzer had minimal differences in accuracy when applied to spectra collected from a sister device. Model transfer was more robust when spectra were trimmed from 910 to 1679 nm to 955-1635 nm due to divergence of edge wavelengths between the two devices. The ability to transfer calibrations between similar single seed NIR spectrometers facilitates broader adoption of this high-throughput, nondestructive, seed phenotyping technology.

Efficient Molecular Marker Design Using the MaizeGDB Mo17 SNPs and Indels Track

Positional cloning in maize (Zea mays) requires development of markers in the region of interest. We found that primers designed to amplify annotated insertion–deletion polymorphisms of seven base pairs or greater between B73 and Mo17 produce polymorphic markers at a 97% frequency with 49% of the products showing co-dominant fragment length polymorphisms. When the same polymorphisms are used to develop markers for B73 and W22 or Mo17 and W22 mapping populations, 22% and 31% of markers are co-dominant, respectively. There are 38,223 Indel polymorphisms that can be converted to markers providing high-density coverage throughout the maize genome. This strategy significantly increases the efficiency of marker development for fine-mapping in maize.

Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control

Crop improvement programs focus on characteristics that are important for plant productivity. Typically genes underlying these traits are identified and stacked to create improved cultivars. Hence, identification of valuable traits for plant productivity is critical for plant improvement. Here we describe an important characteristic for maize productivity. Despite the fact mature maize ears are typically covered with kernels, we find that only a fraction of ovaries give rise to mature kernels. Non-developed ovaries degenerate while neighboring fertilized ovaries produce kernels that fill the ear. Abortion occurs throughout the ear, not just at the tip. We show that the fraction of aborted ovaries/kernels is genetically controlled and varies widely among maize lines, and low abortion genotypes are rare. Reducing or eliminating ovary abortion could substantially increase yield, making this characteristic a new target for selection in maize improvement programs.

Quantitative trait loci associated with soybean seed weight and composition under different phosphorus levels

Seed size and composition are important traits in food crops and can be affected by nutrient availability in the soil. Phosphorus (P) is a non-renewable, essential macronutrient, and P deficiency limits soybean (Glycine max) yield and quality. To investigate the associations of seed traits in low- and high-P environments, soybean recombinant inbred lines (RILs) from a cross of cultivars Fiskeby III and Mandarin (Ottawa) were grown under contrasting P availability environments. Traits including individual seed weight, seed number, and intact mature pod weight were significantly affected by soil P levels and showed transgressive segregation among the RILs. Surprisingly, P treatments did not affect seed composition or weight, suggesting that soybean maintains sufficient P in seeds even in low-P soil. Quantitative trait loci (QTLs) were detected for seed weight, intact pods, seed volume, and seed protein, with five significant QTLs identified in low-P environments and one significant QTL found in the optimal-P environment. Broad-sense heritability estimates were 0.78 (individual seed weight), 0.90 (seed protein), 0.34 (seed oil), and 0.98 (seed number). The QTLs identified under low P point to genetic regions that may be useful to improve soybean performance under limiting P conditions.