The recently identified Mulberry Mosaic Dwarf-associated Virus (MMDaV), associated with mosaic dwarf symptoms in Chinese mulberry leaves, is a newly discovered member of the Geminiviridae family. The MMDaV genome, a single or twin circular single-stranded DNA molecule measuring approximately 2.5-3.0 kb, encodes five proteins and two hypothetical proteins, including a coat protein (CP) and movement protein (MP). The co-evolutionary dynamics between viral and host codon usage significantly impact viral survival, fitness, immune evasion, and evolutionary pathways. This study applied bioinformatic analyses to examine the codon usage bias in thirty MMDaV genomes collected from mulberry leaves in four distinct Chinese provinces. We aimed to understand the drivers of preferred synonymous codon usage. The Effective Number of Codons (ENC) analysis revealed significant regional variations among MMDaV isolates, allowing their classification into two main categories: the southern China HNZX strain and the eastern China HDZX strain. The codon preference analysis displayed a viral preference for using A/U as the terminal base, indicating a bias towards A/U over G/C. Using a combination of position-specific base composition, ENC-Plot, RP2-Plot, Neutral plot, and correspondence analysis, we found that mutational pressure and natural selection substantially influence codon usage and drive MMDaV evolution. Our findings shed light on the complex interplay between MMDaV and its mulberry host and offer crucial insights into the virus's adaptive and evolutionary mechanisms.

To achieve a narrow bandwidth optical filter with a wide swept range for new generation optical spectrum analysis (OSA), an optoelectronic equivalent narrowband filter (OENF) is investigated and a swept optical filter with bandwidth of several MHz and swept range of several ten nanometers is built using electric filters and a swept laser as local oscillator (LO). The principle of OENF is introduced and analysis of OENF system is presented. Two electric filters are optimized to be RBW filters for high and medium spectral resolution application. Both simulations and experiments are conducted to verify OENF principle and results show that power uncertainty is less than 1.2% and spectral resolution can reach 6 MHz. Then, a real-time wavelength calibration system consisting of HCN gas cell and FP etalon is proposed to guarantee a wavelength accuracy of ±0.4 pm at C-band and to reduce the influence of phase noise and nonlinear velocity of swept LO. Finally, experiments on OSA of actual spectra of various optical sensors using OENF system are conducted. Experimental results indicate that OENF system has an excellent capacity in analysis of fine spectrum structures.