Map-based cloning of a new total loss-of-function allele of OsHMA3 causes high cadmium accumulation in rice grain.

Rice (Oryza sativa) is a major dietary source of the toxic metal cadmium (Cd). Reducing Cd transfer from soil to the rice grain is important for food safety. Rice cultivars vary widely in their Cd accumulation, but the genetic basis for this variation is not fully understood. Based on field and pot experiments comparing 26 rice cultivars, we identified a cultivar with high Cd accumulation in grain (BG367, coded as W4) and a cultivar with low grain Cd accumulation (Huajingxian 74, coded as W0). W4 showed a higher Cd translocation from roots to shoots than W0. Using chromosome single segment substitution lines derived from the two cultivars, we mapped a quantitative trait locus for Cd accumulation in grain to a 400 kb region in chromosome 7. Using yeast expression assays and transgenic complementation, we identified OsHMA3 as the causal gene at this locus. Compared with OsHMA3W0, OsHMA3W4 has a deletion of 14 amino acids predicted to be in the ATP binding domain. OsHMA3W4 showed a complete loss of transport activity for Cd in yeast assays. Taking our findings together, we have identified a new allele of OsHMA3 with a total loss-of-function, resulting in greatly elevated Cd translocation to rice shoots and grain.

Application of Trichoderma harzianum SQR-T037 bio-organic fertiliser significantly controls Fusarium wilt and affects the microbial communities of continuously cropped soil of cucumber.

BACKGROUND: The reduction in diversity of the soil microbial community causes the disorder of continuous cropping. The aim of this study was to determine the effects of applying Trichoderma harzianum SQR-T037 bio-organic fertiliser (BIO) on the microbial community in continuously cropped cucumber soil. Four treatments were set: (1) control, where neither seedling nursery soil (N) nor transplanted soil (T) was amended with BIO; (2) N treatment, where nursery soil was amended with BIO (1% w/w) but transplanted soil was not; (3) N + T treatment, where BIO was added to both nursery soil (1% w/w) and transplanted soil (0.5% w/w); (4) uncropped soil, where soil was left uncropped consistently. RESULTS: A disease index of 72.2% was found for the control treatment, while the N and N + T treatments had disease indices of only 25 and 15% respectively. Analysis of the denaturing gradient gel electrophoresis (DGGE) profiles showed that the bacterial communities of the N and N + T treatments were similar to those of the uncropped soil but distinct from those of the control soil. The fungal communities of the N and N + T treatments differed from those of both the uncropped soil and the control. CONCLUSION: Addition of BIO to both the nursery soil and the transplanted soil can diversify the microbial community in continuously cropped cucumber soil and thus effectively control Fusarium wilt of cucumber plants.