The excessive accumulation of copper (Cu²⁺) has become a threat to worldwide crop production. Recently, it was revealed that melatonin (MT) could play a crucial role against heavy metal (HM) stresses in plants. However, the underlying mechanism of MT function acted upon by Cu²⁺ stress (CS) has not been substantiated in tomatoes. In the present work, we produced MT-rich tomato plants by foliar usage of MT, and MT-deficient tomato plants by employing a virus-induced gene silencing methodology and exogenous foliar application of MT synthesis inhibitor para-chlorophenylalanine (pCPA). The obtained results indicate that exogenous MT meaningfully alleviated the dwarf phenotype and impeded the reduction in plant growth caused by excess Cu²⁺. Furthermore, MT effectively restricted the generation of reactive oxygen species (ROS) and habilitated cellular integrity by triggering antioxidant enzyme activities, especially via CAT and APX, but not SOD and POD. In addition, MT increased nonenzymatic antioxidant activity, including FRAP and the GSH/GSSG and ASA/DHA ratios. MT usage improved the expression of several defense genes (CAT, APX, GR and MDHAR) and MT biosynthesis-related genes (TDC, SNAT and COMT). Taken together, our results preliminarily reveal that MT alleviates Cu²⁺ toxicity via ROS scavenging, enhancing antioxidant capacity when subjected to excessive Cu²⁺. These results build a solid foundation for developing new insights to solve problems related to CS.

As a glycophyte plant, pepper (Capsicum annuum L.) is widely cultivated worldwide, but its growth is susceptible to salinity damage, especially at the seedling stage. Here, we conducted a study to determine the physiological and transcriptional differences between two genotype seedlings (P300 and 323F3) with contrasting tolerance under salt stress. The P300 seedlings were more salt-tolerant and had higher K⁺ contents, higher antioxidase activities, higher compatible solutes, and lower Na⁺ contents in both their roots and their leaves than the 323F3 seedlings. During RNA-seq analysis of the roots, more up-regulated genes and fewer down-regulated genes were identified between salt-treated P300 seedlings and the controls than between salt-treated 323F3 and the controls. Many ROS-scavenging genes and several SOS pathway genes were significantly induced by salt stress and exhibited higher expressions in the salt-treated roots of the P300 seedlings than those of 323F3 seedlings. Moreover, biosynthesis of the unsaturated fatty acids pathway and protein processing in the endoplasmic reticulum pathway were deeply involved in the responses of P300 to salt stress, and most of the differentially expressed genes involved in the two pathways, including the genes that encode mega-6 fatty acid desaturases and heat-shock proteins, were up-regulated. We also found differences in the hormone synthesis and signaling pathway genes in both the P300 and 323F3 varieties under salt stress. Overall, our results provide valuable insights into the physiological and molecular mechanisms that affect the salt tolerance of pepper seedlings, and present some candidate genes for improving salt tolerance in pepper.

Simple sequence repeats (SSRs) are widely used in mapping constructions and comparative and genetic diversity analyses. Here, 103,056 SSR loci were found in Cucurbita species by in silico PCR. In general, the frequency of these SSRs decreased with the increase in the motif length, and di-nucleotide motifs were the most common type. For the same repeat types, the SSR frequency decreased sharply with the increase in the repeat number. The majority of the SSR loci were suitable for marker development (84.75% in Cucurbita moschata, 94.53% in Cucurbita maxima, and 95.09% in Cucurbita pepo). Using these markers, the cross-species transferable SSR markers between C. pepo and other Cucurbitaceae species were developed, and the complicated mosaic relationships among them were analyzed. Especially, the main syntenic relationships between C. pepo and C. moschata or C. maxima indicated that the chromosomes in the Cucurbita genomes were highly conserved during evolution. Furthermore, 66 core SSR markers were selected to measure the genetic diversity in 61 C. pepo germplasms, and they were divided into two groups by structure and unweighted pair group method with arithmetic analysis. These results will promote the utilization of SSRs in basic and applied research of Cucurbita species.

Members of homeodomain-leucine zipper (HD-Zip) transcription factors can play their roles by modulating abscisic acid (ABA) signaling in Arabidopsis. So far, our knowledge of the functions of HD-Zips in woodland strawberries (Fragaria vesca), a model plant for studying ABA-mediated fruit ripening, is limited. Here, we identified a total of 31 HD-Zip genes (FveHDZ1-31) in F. vesca, and classified them into four subfamilies (I to IV). Promoter analyses show that the ABA-responsive element, ABRE, is prevalent in the promoters of subfamily I and II FveHDZs. RT-qPCR results demonstrate that 10 of the 14 investigated FveHDZs were consistently >1.5-fold up-regulated or down-regulated in expression in response to exogenous ABA, dehydration, and ABA-induced senescence in leaves. Five of the six consistently up-regulated genes are from subfamily I and II. Thereinto, FveHDZ4, and 20 also exhibited significantly enhanced expression along with increased ABA content during fruit ripening. In yeast one-hybrid assays, FveHDZ4 proteins could bind the promoter of an ABA signaling gene FvePP2C6. Collectively, our results strongly support that the FveHDZs, particularly those from subfamilies I and II, are involved in the ABA-mediated processes in F. vesca, providing a basis for further functional characterization of the HD-Zips in strawberry and other plants.