Comparative transcriptome analysis of differentially expressed genes related to the physiological changes of yellow-green leaf mutant of maize

Genome-Wide Association Study Identified Novel SNPs Associated with Chlorophyll Content in Maize

Chlorophyll is an essential component that captures light energy to drive photosynthesis. Chlorophyll content can affect photosynthetic activity and thus yield. Therefore, mining candidate genes of chlorophyll content will help increase maize production. Here, we performed a genome-wide association study (GWAS) on chlorophyll content and its dynamic changes in 378 maize inbred lines with extensive natural variation. Our phenotypic assessment showed that chlorophyll content and its dynamic changes were natural variations with a moderate genetic level of 0.66/0.67. A total of 19 single-nucleotide polymorphisms (SNPs) were found associated with 76 candidate genes, of which one SNP, 2376873-7-G, co-localized in chlorophyll content and area under the chlorophyll content curve (AUCCC). Zm00001d026568 and Zm00001d026569 were highly associated with SNP 2376873-7-G and encoded pentatricopeptide repeat-containing protein and chloroplastic palmitoyl-acyl carrier protein thioesterase, respectively. As expected, higher expression levels of these two genes are associated with higher chlorophyll contents. These results provide a certain experimental basis for discovering the candidate genes of chlorophyll content and finally provide new insights for cultivating high-yield and excellent maize suitable for planting environment.

Physiological and Biochemical Responses of Sagittaria trifolia L. to Phytotoxic Ethyl Acetate Fungal Extract from Curvularia lunata Strain CLST-01

Curvularia lunata (No. CLST-01), a fungal pathogen isolated from the threeleaf arrowhead (Sagittaria trifolia L.), has been proposed as a potential mycoherbicide for grass weeds. This paper investigated the physiological and biochemical effects of CLST-01 phytotoxic ethyl acetate fungi extract on the leaves of the threeleaf arrowhead. The results showed that the ethyl acetate fungi extract from CLST-01 can accelerate damage to the cell membrane, increase the production of malondialdehyde, and damage the cellular structure, which could decrease the number of chloroplasts after 96 h treatments. In addition, the content of chlorophyll was reduced by 49.5%, and the net photosynthetic rate, stomatal conductance, and transpiration rate were inhibited. The rates of inhibition were 90.13%, 83.74%, and 79.31%, respectively, and the intercellular CO₂ concentration increased by 51.87% on Day 9 after treatment with a concentration of 200 μg/mL. In summary, the phytotoxic ethyl acetate fungal extract from C. lunata CLST-01 can inhibit the photosynthesis of the threeleaf arrowhead leaves, destroy the ultrastructure of leaves, and affect the growth of this invasive weed. Therefore, it has the potential to be developed into a mycoherbicide for weed control in crops as a natural photosynthetic inhibitor.

The wheat leaf delayed virescence of mutant dv4 is associated with the abnormal photosynthetic and antioxidant systems

Chlorophyll (Chl) is a key pigment for wheat (Triticum aestivum L.) photosynthesis, consequently impacts grain yield. A wheat mutant named as delayed virescence 4 (dv4) was obtained from cultivar Guomai 301 (wild type, WT) treated with ethyl methane sulfonate (EMS). The seedling leaves of dv4 were shallow yellow, apparently were chlorophyll deficient. They started to turn green at the jointing stage and returned to almost ordinary green at the heading stage. Leaf transcriptome comparison of Guomai 301 and dv4 at the jointing stage showed that most differentially expressed genes (DEGs) of transcription and translation were highly expressed in dv4, one key gene nicotianamine aminotransferase A (NAAT-A) involved in the synthesis and metabolism pathways of tyrosine, methionine and phenylalanine was significantly lowly expressed. The expression levels of the most photosynthesis related genes, such as photosystem I (PS I), ATPase and light-harvesting chlorophyll protein complex-related homeotypic genes, and protochlorophyllide reductase A (PORA) were lower; but macromolecule degradation and hypersensitivity response (HR) related gene heat shock protein 82 (HSP82) was highly expressed. Compared to WT, the contents of macromolecules such as proteins and sugars were reduced; the contents of Chl a, Chl b, total Chl, and carotenoids in leaves of dv4 were significantly less at the jointing stage, while the ratio of Chl a / Chl b was the same as that of WT. The net photosynthetic rate, stomatal conductance and transpiration rate of dv4 were significantly lower. The H₂O₂ content were higher, while the contents of total phenol and malondialdehyde (MDA), antioxidant enzyme activities were lower in leaves of dv4. In conclusion, the reduced contents of macromolecules and photosynthetic pigments, the abnormal photosynthetic and antioxidant systems were closely related to the phenotype of dv4.

Comparative Transcriptome Analysis Identified Key Pathways and Genes Regulating Differentiated Stigma Color in Melon (Cucumis melo L.)

Stigma color is an important morphological trait in many flowering plants. Visual observations in different field experiments have shown that a green stigma in melons is more attractive to natural pollinators than a yellow one. In the current study, we evaluated the characterization of two contrasted melon lines (MR-1 with a green stigma and M4-7 with a yellow stigma). Endogenous quantification showed that the chlorophyll and carotenoid content in the MR-1 stigmas was higher compared to the M4-7 stigmas. The primary differences in the chloroplast ultrastructure at different developmental stages depicted that the stigmas of both melon lines were mainly enriched with granum, plastoglobulus, and starch grains. Further, comparative transcriptomic analysis was performed to identify the candidate pathways and genes regulating melon stigma color during key developmental stages (S1–S3). The obtained results indicated similar biological processes involved in the three stages, but major differences were observed in light reactions and chloroplast pathways. The weighted gene co-expression network analysis (WGCNA) of differentially expressed genes (DEGs) uncovered a “black” network module (655 out of 5302 genes), mainly corresponding to light reactions, light harvesting, the chlorophyll metabolic process, and the chlorophyll biosynthetic process, and exhibited a significant contribution to stigma color. Overall, the expression of five key genes of the chlorophyll synthesis pathway—CAO (MELO03C010624), CHLH (MELO03C007233), CRD (MELO03C026802), HEMA (MELO03C011113), POR (MELO03C016714)—were checked at different stages of stigma development in both melon lines using quantitative real time polymerase chain reaction (qRT-PCR). The results exhibited that the expression of these genes gradually increased during the stigma development of the MR-1 line but decreased in the M4-7 line at S2. In addition, the expression trends in different stages were the same as RNA-seq, indicating data accuracy. To sum up, our research reveals an in-depth molecular mechanism of stigma coloration and suggests that chlorophyll and related biological activity play an important role in differentiating melon stigma color.

Genetic mapping and physiological analysis of chlorophyll-deficient mutant in Brassica napus L

BACKGROUND

Leaf color mutants have reduced photosynthetic efficiency, which has severely negative impacts on crop growth and economic product yield. There are different chlorophyll mutants in Arabidopsis and crops that can be used for genetic control and molecular mechanism studies of chlorophyll biosynthesis, chloroplast development and photoefficiency. Chlorophyll mutants in Brassica napus are mostly used for mapping and location research but are rarely used for physiological research. The chlorophyll-deficient mutant in this experiment were both genetically mapped and physiologically analyzed.

RESULTS

In this study, yellow leaf mutant of Brassica napus L. mutated by ethyl methyl sulfone (EMS) had significantly lower chlorophyll a, b and carotenoid contents than the wild type, and the net photosynthetic efficiency, stomatal conductance and transpiration rate were all significantly reduced. The mutant had sparse chloroplast distribution and weak autofluorescence. The granule stacks were reduced, and the shape was extremely irregular, with more broken stromal lamella. Transcriptome data analysis enriched the differentially expressed genes mainly in phenylpropane and sugar metabolism. The mutant was mapped to a 2.72 Mb region on A01 by using BSA-Seq, and the region was validated by SSR markers.

CONCLUSIONS

The mutant chlorophyll content and photosynthetic efficiency were significantly reduced compared with those of the wild type. Abnormal chloroplasts and thylakoids less connected to the stroma lamella appeared in the mutant. This work on the mutant will facilitate the process of cloning the BnaA01.cd gene and provide more genetic and physiological information concerning chloroplast development in Brassica napus.