Nan Gao

Transgenic tomato overexpressing ath-miR399d has enhanced phosphorus accumulation through increased acid phosphatase and proton secretion as well as phosphate transporters

By generating and examining transgenic tomato overexpressing ath-miR399d grown in hydroponic conditions, in quartz sand, or in a polytunnel greenhouse vegetable soil culture, this study aimed to investigate the effects of miR399d from Arabidopsis on phosphorus (P) accumulation, P concentrations in transgenic tomato overexpressing ath-miR399d shoots, phosphate transporter expression, and proton secretion and acid phosphatase (APase) activity in roots. In the transgenic tomato, leaf P concentration increased significantly in an agricultural soil, and roots had higher uptake of P, as evidenced by leaf P concentrations and relative expression of the genes LePT1, LePT2, LePT4, and LePT5 in normal-P solution. Enhanced APase activity in transgenic roots and the outside medium led to superior hydrolysis of organic P, and increased proton extrusion by roots led to superior dissolution of AlPO4. Thus, besides phosphate transporters, higher APase activity and strengthened acidification in the vicinity of the roots may be important mechanisms for transgenic tomato to scavenge or acquire P in soil. These results provide new understanding of miR399-overexpressing plants that accumulate excess P in shoots.

Influences of past application rates of nitrogen and a catch crop on soil microbial communities between an intensive rotation

The aim of this study was to investigate influences of six-year past application rates of nitrogen and a catch crop, sweet corn (Zea mays L. ssp. Saccharata Sturt), on soil microbial community and diversity in a greenhouse-based intensive vegetable soil in eastern China. Soil electrical conductivity, pH, mineral nitrogen, phospholipid fatty acids (PLFA) profiles and carbon source utilization patterns under five annually past nitrogen rates (0, 348, 522, 696 and 870 kg nitrogen ha−1) were evaluated after the establishment of sweet corn during 1–1.5-month fallow period over three-year tomato/cucumber/celery rotations. The past nitrogen application rates exerted significant effects on soil electrical conductivity, pH, nitrate-nitrogen, ammonium-nitrogen and carbon source utilization patterns, but not on PLFAs profiles. The sweet corn had a significant effect on soil chemical properties, total and actinobacterial PLFAs, but not on carbon source utilization patterns. Soil electrical conductivity, nitrate-nitrogen and the total PLFAs decreased whilst soil organic carbon, pH and the actinobacterial PLFAs increased after the establishment of sweet corn. Soil microbial functional diversity from carbon source utilization patterns and actinobacterial PLFAs were greatest after the establishment of sweet corn at a 60% of the conventional nitrogen rate (i.e. 522 kg nitrogen ha−1). Soil electrical conductivity and ammonium-nitrogen were two key factors to determine carbon source utilization patterns, whilst soil pH was the key factor to determine PLFAs profiles. A combination of the catch crop sweet corn during summer fallow and a 60% of the conventional nitrogen rate is a sustainable pathway of utilizing greenhouse-based intensive vegetable soils in eastern China.

Influence of transgenic ath-miR399d tomato lines on microbial community and diversity in rhizosphere soil

Abstract Transgenic ath-miR399d tomatoes (Solanum lycopersicum L. cv Zhongshu No. 4) have enhanced phosphorus (P) uptake and accumulation in shoots, and have the potential to improve P-use efficiency in agricultural soils. However, the effects of transgenic ath-miR399d tomatoes on soil microbial community and diversity are poorly understood. Soil carbon source utilization patterns and phospholipid fatty acid (PLFA) profiles were evaluated after a 35-d cultivation of transgenic tomato lines C1 and C2 and wild-type tomato at 0, 150 and 300 mg phosphorus pentoxide (P2O5) kg−1 soil. Microbial diversity indices deduced from carbon source utilization patterns were significantly decreased after cultivating transgenic tomato lines compared to wild-type tomato. So were the average well color development (AWCD) for general carbon sources, carbohydrates and amino acids. The AWCD for general carbon sources was increased with P levels, while the microbial diversity indices did not differ significantly among three P levels. The amounts of total, bacterial and Gram-positive bacterial PLFA significantly declined after cultivating transgenic tomato lines. So were Gram-negative bacterial PLFA at 0 and 150 mg P2O5 kg−1 soil. In contrast, the numbers of individual PLFA, the PLFA ratio of fungi:bacteria and Gram-positive bacteria:Gram-negative bacteria were not significantly affected by genotype or P level after the 35-d cultivation of transgenic tomato lines. Principal component analysis (PCA) for both substrate utilization patterns and PLFA profiles showed good separation of soil microbial communities between the transgenic tomato lines and wild-type tomato. Our results suggest that transgenic ath-miR399d tomatoes have transient adverse effects on microbial community and diversity in rhizosphere soil.

Transgenic tomato overexpressing ath-miR399d improves growth under abiotic stress conditions

Phosphorus (P) is an essential element required for plant growth and development. Abiotic stresses, such as cold and P deficiency cause adverse effects on growth of plants, inhibit accumulation or translocation of mineral nutrients such as P, and often constrain the productivity and quality of crops. miR399 as a long-distance signal controls systemic phosphate homeostasis by modulating phosphate uptake and transport. However, overexpression of miR399 causes P toxicity and results in retarded growth. Thus, we constructed a transgenic tomato (Solanum lycopersicum L., C1), which contains foreign gene ath-miR399d under the control of rd29A promoter. In the transgenic C1 expression of the miR399d gene showed a stress-inducible pattern. Results showed that miR399d was moderately up-regulated in response to salinity and cold stresses. In soil, dry weight was enhanced in transgenic tomato under low temperature and P deficiency conditions. The transgenic tomato has potential to improve growth when it is exposed to other abiotic stresses such as salinity and drought.