Genetic and physiological analyses of root cracking in radish (Raphanus sativus L.)

Genome-Wide Identification of the CDPK Gene Family and Their Involvement in Taproot Cracking in Radish

Taproot cracking, a severe and common physiological disorder, markedly reduces radish yield and commercial value. Calcium-dependent protein kinase (CDPK) plays a pivotal role in various plant developmental processes; however, its function in radish taproot cracking remains largely unknown. Here, 37 RsCDPK gene members were identified from the long-read radish genome "QZ-16". Phylogenetic analysis revealed that the CDPK members in radish, tomato, and Arabidopsis were clustered into four groups. Additionally, synteny analysis identified 13 segmental duplication events in the RsCDPK genes. Analysis of paraffin-embedded sections showed that the density and arrangement of fleshy taproot cortex cells are important factors that affect radish cracking. Transcriptome sequencing of the fleshy taproot cortex revealed 5755 differentially expressed genes (DEGs) (3252 upregulated and 2503 downregulated) between non-cracking radish "HongYun" and cracking radish "505". These DEGs were significantly enriched in plant hormone signal transduction, phenylpropanoid biosynthesis, and plant-pathogen interaction KEGG pathways. Furthermore, when comparing the 37 RsCDPK gene family members and RNA-seq DEGs, we identified six RsCDPK genes related to taproot cracking in radish. Soybean hairy root transformation experiments showed that RsCDPK21 significantly and positively regulates root length development. These findings provide valuable insights into the relationship between radish taproot cracking and RsCDPK gene function.

Role of Different Abiotic Factors in Inducing Pre-Harvest Physiological Disorders in Radish (Raphanus sativus)

Radish, one of the important root vegetables, is widely grown in the world due to its easy cultivation, short duration, growing habit, and adaptability to various growing conditions. However, it is still extremely difficult to produce good quality radish roots due to its vulnerability to different preharvest physiological disorders. Important physiological disorders that significantly reduce the yield and quality of radish are forking, pithiness/sponginess, cracking/splitting, hollowness, and internal browning. Different abiotic factors like moisture stress, temperature fluctuation, growing medium, nutrient imbalance, plant density and harvesting time cause a disturbance in the metabolic activities of root tissues that produce non-marketable roots. Therefore, this review provides a detail insight on the causes, physiology of these disorders, and the management practices to prevent them to produce commercial quality roots. This comprehensive knowledge will not only help the growers, but it will provide relative information for researchers as well to control these disorders through breeding innovations and biotechnological tools.

Downregulation of the photosynthetic machinery and carbon storage signaling pathways mediate La2O3 nanoparticle toxicity on radish taproot formation

The molecular and physiological mechanisms of how rare earth oxide nanoparticles (NPs) alter radish (Raphanus sativus L.) taproot formation and cracking were investigated in the present study. We compared plants that received suspensions of 10, 50, 100, 300 mg L^-1 of La₂O₃ NPs, 300 m L^-1 La₂O₃ bulk-particles (BPs), 0.8 m L^-1 La³⁺, or only water for six days during their tuber formation period. 100 and 300 mg L^-1 La₂O₃ NPs exposure decreased storage root biomass by 38% and 60%, respectively, and they both induced visible root cracking. Physiological analyses showed that La₂O₃ NPs exposure (>100 mg L^-1) significantly inhibited leaf net photosynthetic rate, cell wall pectin synthesis of both storage root epidermis and xylem parenchyma tissues, but increased the contents of cellulose and hemicellulose 1 in root epidermis cell walls. Moreover, transcriptome analysis further found that La₂O₃ NPs changed root cell wall structure by down-regulating core genes involved in cell wall pectin and IAA biosynthesis, which coincided with the observed La₂O₃ NPs-induced root cracking. Our results revealed the molecular mechanisms related to cell wall carbohydrate metabolism in response to NPs stress, providing a step forward for understanding the causes of NPs phytotoxicity on edible plant taproot formation and cracking.