The rarest codon in the high G+C genome of Streptomyces coelicolor is TTA, corresponding in mRNA to the UUA codon that is recognized by a developmentally important tRNA encoded by the bldA gene. There are 145 TTA-containing genes in the chromosome of S. coelicolor. Only 42 of these are represented in the genome of Streptomyces avermitilis, among which only 12 have a TTA codon in both species. The TTA codon is less represented in housekeeping genes and orthologous genes, and is more represented in functional-unknown, extrachromosomal or weakly expressed genes. Twenty one TTA-containing chromosomal genes in S. coelicolor were disrupted, including 12 of the 42 genes that are common to both S. avermitillis and S. coelicolor. None of the mutant strains showed any obvious phenotypic differences from the wild-type strain under tested conditions. Possible reasons for this, and the role and evolution of the observed distribution of TTA codons among Streptomyces genes were discussed.
To improve the overall mechanization level of rapeseed production in China, especially in some hilly regions where ground machinery cannot enter the fields or can only enter with very low economic benefits, a special aerial seeding system for rapeseed based on a miniature air-assisted centralized metering device was designed and tested in this study. Unlike existing commercial aerial seeding systems, the proposed seed meter was a miniaturized version derived from the traditional air-feeding seed meter on ground planters. The new version contained a redesigned seed feeding component to overcome problems of serious air backflow to the seed box and difficult seed feeding after miniaturization. Three groups of experiments were designed and conducted to optimize the parameters of the seed meter and test its performance. Results from the orthogonal experiment showed that the seed feeding component performed best when the seed layer thickness was 45 mm, the rotational speed of the gear disc was 45 r/min, and the airflow pressure was 2450 Pa. Results from the static workbench test showed that the designed seeding system had a maximum average total sowing efficiency of 537.17 g/min, with the maximum values of the stability variation coefficient of total seeding rate (seven ports) and the consistency variation coefficient between each port was 2.37% and 4.89%, respectively. Field tests further proved that the designed aerial seeding system could work stably, uniformly, and efficiently, so that the agronomic requirements of rape crop planting could be well met.
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