Chemical composition analysis and transcriptomics reveal the R2R3-MYB genes and phenol oxidases regulating the melanin formation in black radish.

Melanins are dark-brown to black-colored biomacromolecules which have been thoroughly studied in animals and microorganisms. However, the biochemical and molecular basis of plant melanins are poorly understood. We first characterized melanin from the black radish (Raphanus sativus var. niger) 'HLB' through spectroscopic techniques. p-Coumaric acid was identified as the main precursor of radish melanin. Moreover, a joint analysis of transcriptome and coexpression network was performed for the two radish accessions with black and white cortexes, 'HLB' and '55'. A set of R2R3-type RsMYBs and enzyme-coding genes exhibited a coexpression pattern, and were strongly correlated with melanin formation in radish. Transient overexpression of two phenol oxidases RsLAC7 (laccase 7) or RsPOD22-1 (peroxidase 22-1) resulted in a deeper brown color around the infiltration sites and a significant increase in the total phenol content. Furthermore, co-injection of the transcriptional activator RsMYB48/RsMYB97 with RsLAC7 and/or RsPOD22-1, markedly increased the yield of black extracts. Spectroscopic analyses revealed that these extracts are similar to the melanin found in 'HLB'. Our findings advance the understanding of structural information and the transcriptional regulatory mechanism underlying melanin formation in radish.

Dynamic profiling of intact glucosinolates in radish by combining UHPLC-HRMS/MS and UHPLC-QqQ-MS/MS.

Glucosinolates (GSLs) and their degradation products in radish confer plant defense, promote human health, and generate pungent flavor. However, the intact GSLs in radish have not been investigated comprehensively yet. Here, an accurate qualitative and quantitative analyses of 15 intact GSLs from radish, including four major GSLs of glucoraphasatin (GRH), glucoerucin (GER), glucoraphenin (GRE), and 4-methoxyglucobrassicin (4MGBS), were conducted using UHPLC-HRMS/MS in combination with UHPLC-QqQ-MS/MS. Simultaneously, three isomers of hexyl GSL, 3-methylpentyl GSL, and 4-methylpentyl GSL were identified in radish. The highest content of GSLs was up to 232.46 µmol/g DW at the 42 DAG stage in the 'SQY' taproot, with an approximately 184.49-fold increase compared to the lowest content in another sample. That the GSLs content in the taproots of two radishes fluctuated in a similar pattern throughout the five vegetative growth stages according to the metabolic profiling, whereas the GSLs content in the '55' leaf steadily decreased over the same period. Additionally, the proposed biosynthetic pathways of radish-specific GSLs were elucidated in this study. Our findings will provide an abundance of qualitative and quantitative data on intact GSLs, as well as a method for detecting GSLs, thus providing direction for the scientific progress and practical utilization of GSLs in radish.

Genetic Diversity Analysis and Core Germplasm Collection Construction of Radish Cultivars Based on Structure Variation Markers.

Radish is an economically important root vegetable worldwide. In this study, the 217 cultivated radish accessions were collected and genotyped. To detect the genotypes of these accessions, a total of 24 structure variation (SV) markers distributed on nine chromosomes were employed to analyze genetic diversity and construct a core germplasm collection of radish. The results of polymorphism information content (PIC) indicated a good polymorphism of these SV markers. Population structure analysis and principal component analysis (PCA) results showed that the 217 radish accessions fell into three main populations (P1, P2, and P3). Genetic diversity analysis showed that these populations were highly associated with geographical distribution. The values of the fixation index (FST) indicated a high genetic diversity between P2 and P3, and a moderate genetic diversity between P1 and P2, and P1 and P3. Furthermore, the 43 core germplasm were exploited for creating cytoplasmic male sterility (CMS) lines and cultivating new radish varieties. The high genetic diversity of 217 radish germplasms will not only provide valuable resources for future genetic mapping and functional genomic research, but also facilitate core germplasm utilization and the molecular breeding of radish.

Analysis of bacterial communities in rhizosphere soil of continuously cropped healthy and diseased konjac.

The bacterial community and diversity in healthy and diseased konjac rhizosphere soils with different ages of continuous cropping were investigated using next-generation sequencing. The results demonstrated that the number of years of continuous cropping significantly altered soil bacterial community and diversity. Soil bacterial Shannon diversity index and Chao 1 index decreased with the increasing cropping years of konjac. After 1 year of cropping, the soil exhibited the highest bacterial relative abundance and diversity. Of the 44 bacterial genera (relative abundance ratio of genera greater than 0.3%), 14 were significantly affected by the duration of continuous cropping and plant status. With increasing continuous cropping, Alicyclobacillus decreased, while Achromobacter, Lactobacillus, Kaistobacter, Rhodoplanes increased after 3 years continuous cropping. Continuous cropping altered the structure and composition of the soil bacterial community, which led to the reduction in the beneficial bacteria and multiplication of harmful bacteria. These results will improve our understanding of soil microbial community regulation and soil health maintenance in konjac farm systems.

Early season host plants of Apolygus lucorum (Heteroptera: Miridae) in northern China.

Apolygus lucorum (Meyer-Dür) (Heteroptera: Miridae) has become a severe pest of cotton and many other crops in northern China as a result of the widespread adoption of Bacillus thuringiensis (Berliner) cotton, with a corresponding reduction of broad-spectrum insecticide application in cotton fields. From the middle of April to middle June, A. lucorum feeds and develops on other host plants before dispersing to cotton fields. Effective suppression of A. lucorum populations before they enter cotton fields may be an excellent strategy for reducing the occurrence and damage of their subsequent generations in cotton fields. For that, basic information about the host plant range of A. lucorum during the early season is needed. Between 2006 and 2010, a total of 94 plant species from 41 families covering 39,956 square meters of land in natural conditions were sampled using the standard white pan beat method. Sixty-six plant species, including 45 weeds, 10 fruit trees, 5 timber trees, 4 pasture crops, and 2 arable crops were found to be hosts of A. lucorum. Among these species, Descurainia sophia (L.) Webb ex Prantl, Humulus scandens (Loureiro) Merrill, Zizyphus jujuba Miller, Vitis vinifera L., Viciafaba L., and Medicago sativa L. were identified as dominant host species because of their wide distribution and high population densities of A. lucorum. The results of this study provide useful information about the early season host range of A. lucorum, which can be used to develop effective strategies to control the pest before its dispersal to cotton fields.