Lei Zhang

The regulatory mechanism of brassinolide (BR) signaling in cucurbitaceae crops remains incompletely understood. Previous research demonstrated that the rice genes GW5 and GW5L modulate seed morphology via the BR pathway. However, the conservation of their orthologs in watermelon and their evolutionary trajectory are yet to be elucidated. In this study utilizing the watermelon 97103v2 genome, we identified 15 GW5-LIKE genes. Through structure, phylogenetic tree construction, collinearity, promoter and spatiotemporal expression analysis, we determined that ClGL1 to ClGL3 are the most closely related to GW5 and GW5L. Subsequently, two crucial materials were acquired: the inbred line Jing L6M harboring the homozygous mutant Clgl1, and the near-isogenic line Changhong, a Jing L6M backcross containing the wild-type allele ClGL1. Apart from the disparity in fruit morphology, a clear difference in seed shape was observed between the two. Furthermore, exogenous BR treatment demonstrated that ClGL1 positively regulated the BR signal, aligning with the positive impact of GW5 and GW5L. In conclusion, ClGL1 modulates the morphology of watermelon fruit and seed by enhancing BR signaling, which provides a key gene and theoretical basis for BR signaling evolution and molecular design breeding in Cucurbitaceae.

In plants, the accumulation of carotenoids can maintain the balance of the photosystem and improve crop nutritional quality. Therefore, the molecular mechanisms underlying carotenoid synthesis and accumulation should be further explored. In this study, carotenoid accumulation differed significantly among parental Brassica rapa. Genetic analysis was carried out using the golden inner leaf ‘1900264′ line and the light−yellow inner leaf ‘1900262′ line, showing that the golden inner leaf phenotype was controlled by a single dominant gene. Using bulked−segregant analysis sequencing, BraA09g007080.3C encoding the ORANGE protein was selected as a candidate gene. Sequence alignment revealed that a 4.67 kb long terminal repeat insertion in the third exon of the BrGOLDEN resulted in three alternatively spliced transcripts. The spatiotemporal expression results indicated that BrGOLDEN might regulate the expression levels of carotenoid−synthesis−related genes. After transforming BrGOLDEN into Arabidopsis thaliana, the seed−derived callus showed that BrGOLDEN_Ins and BrGOLDEN_Del lines presented a yellow color and the BrGOLDEN_Ldel line presented a transparent phenotype. In addition, using the yeast two−hybrid assay, BrGOLDEN_Ins, BrGOLDEN_Ldel, and Brgolden_wt exhibited strong interactions with BrPSY1, but BrGOLDEN_Del did not interact with BrPSY1 in the split−ubiquitin membrane system. In the secondary and 3D structure analysis, BrGOLDEN_Del was shown to have lost the PNFPSFIPFLPPL sequences at the 125 amino acid position, which resulted in the α−helices of BrGOLDEN_Del being disrupted, restricting the formation of the 3D structure and affecting the functions of the protein. These findings may provide new insights into the regulation of carotenoid synthesis in B. rapa.

Turnip mosaic virus (TuMV), which is distributed almost all over the world and has a wide range of hosts, mainly brassica crops, was first described in Brassica rapa in the USA. Plant volatile compounds play an important role in the host searching behavior of natural enemies of herbivorous insects. In this study, TuMV-inoculated resistant and susceptible B. rapa lines were tested using volatile metabolome and transcriptome analyses. In volatile metabolome analysis, the volatile organic compounds (VOCs) were different after inoculation with TuMV in resistant B80124 and susceptible B80461, and the degree of downregulation of differentially expressed metabolites was more obvious than the degree of upregulation. Through transcriptome analysis, 70% of differentially expressed genes were in biological process, especially focusing on defense response, flavonoid biosynthetic process, and toxin metabolic process, which indicates that TuMV stress maybe accelerate the increase of VOCs. Integrating the metabolome and transcriptome analyses, after inoculating with TuMV, auxin regulation was upregulated, and ARF, IAA and GH3 were also upregulated, which accelerated cell enlargement and plant growth in tryptophan metabolism. The different genes in zeatin biosynthesis pathways were downregulated, which reduced cell division and shoot initiation. However, the metabolite pathways showed upregulation in brassinosteroid biosynthesis and α-linolenic acid metabolism, which could cause cell enlargement and a stress response. This study determined the difference in volatiles between normal plants and infected plants and may lay a foundation for anti-TuMV research in B. rapa.