Chloroplasts are the material basis of photosynthesis, and temperature and light severely affect chloroplast development and thus influence photosynthetic efficiency. This study identified a spontaneous virescent leaf mutant, SC311Y, whose cotyledons and true leaves were yellow and gradually turned green. However, temperature and light affected the process of turning green. In addition, this mutant (except at the seedling stage) had ruffled leaves with white stripes, sterile males, and poorly fertile female flowers. Genetic characteristics analysis revealed that the recessive gene controlled the virescent leaf. Two F2 populations mapped v-3 to the interval of 33.54–35.66 Mb on chromosome 3. In this interval, BSA-Seq, RNA-Seq, and cDNA sequence analyses revealed only one nonsynonymous mutation in the Csa3G042730 gene, which encoded the RNA exosome supercomplex subunit resurrection1 (RST1). Csa3G042730 was predicted to be the candidate gene controlling the virescent leaf, and the candidate gene may regulate chloroplast development by regulating plastid division2 (PDV2). A transcriptome analysis showed that different factors caused the reduced chlorophyll and carotenoid content in the mutants. To our knowledge, this study is the first report of map-based cloning related to virescent leaf, male-sterile, and chloroplast RNA regulation in cucumber. The results could accelerate the study of the RNA exosome supercomplex for the dynamic regulation of chloroplast RNA.
Polygalacturonase (PG) gene has been documented as a key candidate for the improvement of fruit firmness, which is a target trait for tomato production because it facilitates transportation and storage. To reduce the expression of the PG gene, most of the elite commercial tomato varieties were obtained by RNA interference technology. However, this approach of producing commercialized tomatoes by integration of the exogenous gene is controversial. In this work, CRISPR/Cas9 technology was used to induce the targeted mutagenesis of the SlPG gene to delay the softening of tomato fruit. Results showed that the SlPG gene was frameshift mutated by 4 bp deletion, 10 bp deletion, and 1 bp insertion, which generated premature translation termination codons. Compared with wild-type (WT), homozygous T1-generation tomato plants exhibited late fruit softening under natural conditions. Consistent with this phenomenon, the firmness value of WT fruit was lower in slpg mutant fruit, and the physiological loss of water was higher. Collectively, these data demonstrate that the mutation of the SlPG gene delays tomato fruit softening. More importantly, 8 out of 20 transgene-free tomato plants, which were homozygous for null alleles of SlPG, were separated in the T3-generation of line slpgT2-#2. This transgene-free slpg may provide materials for more in-depth research of SlPG functions and the molecular mechanism of fruit softening in tomatoes.
Iron (Fe) deficiency is a common abiotic stress in plants grown in alkaline soil that causes leaf chlorosis and affects root development due to low plant-available Fe concentration. Silicon (Si) is a beneficial element for plant growth and can also improve plant tolerance to abiotic stress. However, the effect of Si and regulatory mechanisms on tomato plant growth under Fe deficiency remain largely unclear. Here, we examined the effect of Si application on the photosynthetic capacity, antioxidant defense, sugar metabolism, and organic acid contents under Fe deficiency in tomato plants. The results showed that Si application promoted plant growth by increasing photosynthetic capacity, strengthening antioxidant defense, and reprogramming sugar metabolism. Transcriptomics analysis (RNA-seq) showed that Si application under Fe deficiency up-regulated the expression of genes related to antioxidant defense, carbohydrate metabolism and organic acid synthesis. In addition, Si application under Fe deficiency increased Fe distribution to leaves and roots. Combined with physiological assessment and molecular analysis, these findings suggest that Si application can effectively increase plant tolerance to low Fe stress and thus can be implicated in agronomic management of Fe deficiency for sustainable crop production. Moreover, these findings provide important information for further exploring the genes and underlying regulatory mechanisms of Si-mediated low Fe stress tolerance in crop plants.
Zucchini (Cucurbita pepo L.) is one of the main vegetable crops grown under protected cultivation in northern China. Low-temperature (LT) stress severely inhibits the growth of zucchini seedlings, resulting in reductions in yield and quality. Here, using three kinds of different humic acids, including coal-based humic acid (CHA), fulvic acid (FA), and biochemical humic acid (BHA), we investigated the effects of humic acids against LT stress (5°C) in zucchini seedlings. Treatment with all three kinds of humic acids improves LT stress tolerance by decreasing oxidative damage through increases in antioxidative enzyme activities and the contents of soluble sugar and proline in zucchini seedlings, especially after BHA application. Comparative transcriptomic analysis revealed that a total of 17 differentially expressed genes (DEGs) were commonly induced in the leaves of FA-, CHA-, and BHA-treated zucchini seedlings under LT stress, including calmodulin, ethylene-responsive transcription factors (TFs), peroxidases, and 10 TFs, including two NAC and seven WRKY genes. Altogether, these results indicated that supplementation with humic acids reprograms plant metabolism and modulates the expression of genes involved in ROS scavenging, phytohormone metabolism, or signaling pathways, finally improving LT stress tolerance in zucchini seedlings.
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