Plant trichomes formed by specialized epidermal cells play a role in protecting plants from biotic and abiotic stresses and can also influence the economic and ornamental value of plant products. Therefore, further studies on the molecular mechanisms of plant trichome growth and development are important for understanding trichome formation and agricultural production. SET Domain Group 26 (SDG26) is a histone lysine methyltransferase. Currently, the molecular mechanism by which SDG26 regulates the growth and development of Arabidopsis leaf trichomes is still unclear. We found that the mutant of Arabidopsis (sdg26) possessed more trichomes on its rosette leaves compared to the wild type (Col-0), and the trichome density per unit area of sdg26 is significantly higher than that of Col-0. The content of cytokinins and jasmonic acid was higher in sdg26 than in Col-0, while the content of salicylic acid was lower in sdg26 than in Col-0, which is conducive to trichome growth. By measuring the expression levels of trichome-related genes, we found that the expression of genes that positively regulate trichome growth and development were up-regulated, while the negatively regulated genes were down-regulated in sdg26. Through chromatin immunoprecipitation sequencing (ChIP-seq) analysis, we found that SDG26 can directly regulate the expression of genes related to trichome growth and development such as ZFP1, ZFP5, ZFP6, GL3, MYB23, MYC1, TT8, GL1, GIS2, IPT1, IPT3, and IPT5 by increasing the accumulation of H3K27me3 on these genes, which further affects the growth and development of trichomes. This study reveals the mechanism by which SDG26 affects the growth and development of trichomes through histone methylation. The current study provides a theoretical basis for studying the molecular mechanism of histone methylation in regulating leaf trichome growth and development and perhaps guiding the development of new crop varieties.

Low temperature is a major environmental factor, which limits rapeseed (Brassica napus L.) growth, development, and productivity. So far, the physiological and molecular mechanisms of rapeseed responses to cold stress are not fully understood. Here, we explored the transcriptome and metabolome profiles of two rapeseed genotypes with contrasting cold responses, i.e., XY15 (cold-sensitive) and GX74 (cold-tolerant). The global metabolome profiling detected 545 metabolites in siliques of both genotypes before (CK) and after cold-stress treatment (LW). The contents of several sugar metabolites were affected by cold stress with the most accumulated saccharides being 3-dehydro-L-threonic acid, D-xylonic acid, inositol, D-mannose, D-fructose, D-glucose, and L-glucose. A total of 1943 and 5239 differentially expressed genes were identified from the transcriptome sequencing in XY15CK_vs_XY15LW and GX74CK_vs_GX74LW, respectively. We observed that genes enriched in sugar metabolism and biosynthesis-related pathways, photosynthesis, reactive oxygen species scavenging, phytohormone, and MAPK signaling were highly expressed in GX74LW. In addition, several genes associated with cold-tolerance-related pathways, e.g., the CBF-COR pathway and MAPK signaling, were specifically expressed in GX74LW. Contrarily, genes in the above-mentioned pathways were mostly downregulated in XY15LW. Thus, our results indicate the involvement of these pathways in the differential cold-stress responses in XY15 and GX74.

Cold stress affects the seed germination and early growth of winter rapeseed, leading to yield losses. We employed transmission electron microscopy, physiological analyses, metabolome profiling, and transcriptome sequencing to understand the effect of cold stress (0 °C, LW) on the cotyledons of cold-tolerant (GX74) and -sensitive (XY15) rapeseeds. The mesophyll cells in cold-treated XY15 were severely damaged compared to slightly damaged cells in GX74. The fructose, glucose, malondialdehyde, and proline contents increased after cold stress in both genotypes; however, GX74 had significantly higher content than XY15. The pyruvic acid content increased after cold stress in GX74, but decreased in XY15. Metabolome analysis detected 590 compounds, of which 32 and 74 were differentially accumulated in GX74 (CK vs. cold stress) and XY15 (CK vs. cold stressed). Arachidonic acid and magnoflorine were the most up-accumulated metabolites in GX74 subjected to cold stress compared to CK. There were 461 and 1481 differentially expressed genes (DEGs) specific to XY15 and GX74 rapeseeds, respectively. Generally, the commonly expressed genes had higher expressions in GX74 compared to XY15 in CK and cold stress conditions. The expression changes in DEGs related to photosynthesis-antenna proteins, chlorophyll biosynthesis, and sugar biosynthesis-related pathways were consistent with the fructose and glucose levels in cotyledons. Compared to XY15, GX74 showed upregulation of a higher number of genes/transcripts related to arachidonic acid, pyruvic acid, arginine and proline biosynthesis, cell wall changes, reactive oxygen species scavenging, cold-responsive pathways, and phytohormone-related pathways. Taken together, our results provide a detailed overview of the cold stress responses in rapeseed cotyledons.