Chloroplast development and chlorophyll(Chl)metabolism in unripe tomato contribute to the growth and quality of the fruit, however these mechanisms are poorly understood. In this study, we initially investigated seven homeobox-containing transcription factors (TFs) with specific ripening-associated expression patterns using virus-induced gene silencing (VIGS) technology and found that inhibiting the expression of one of these TFs, BEL1-LIKE HOMEODOMAIN11 (SlBEL11), significantly increased Chl levels in unripe tomato fruit. This enhanced Chl accumulation was further validated by generating stable RNA interference (RNAi) transgenic lines. RNA sequencing (RNA-seq) of RNAi-SlBEL11 fruit at the mature green (MG) stage showed that 48 genes involved in Chl biosynthesis, photosynthesis and chloroplast development were significantly upregulated compared with the wild type (WT) fruit. Genomic global scanning for Homeobox TF binding sites combined with RNA-seq differential gene expression analysis showed that 22 of these 48 genes were potential target genes of SlBEL11 protein. These genes included Chl biosynthesis-related genes encoding for protochlorophyllide reductase (POR), magnesium chelatase H subunit (CHLH) and chlorophyllide a oxygenase (CAO), and chloroplast development-related genes encoding for chlorophyll a/b binding protein (CAB), homeobox protein knotted 2 (TKN2) and ARABIDOPSIS PSEUDO RESPONSE REGULATOR 2-LIKE (APRR2-like). Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation quantitative polymerase chain reaction (PCR) (ChIP-qPCR) assays were employed to verify that SlBEL11 protein could bind to the promoters for TKN2, CAB and POR. Taken together, our findings demonstrated that SlBEL11 plays an important role in chloroplast development and Chl synthesis in tomato fruit.

Steroidal glycoalkaloids (SGAs) are cholesterol-derived specialized metabolites produced by Solanaceous plant species. They contribute to pathogen defense but are considered as anti-nutritional compounds and toxic to humans. Although the genes involved in the SGA biosynthetic pathway have been successfully cloned and identified, transcription factors regulating this pathway are still poorly understood. We report that silencing tomato light signal transduction transcription factors ELONGATED HYPOCOTYL 5 (SlHY5) and PHYTOCHROME INTERACTING FACTOR3 (SlPIF3), by virus-induced gene silencing (VIGS), altered glycoalkaloids levels in tomato leaves compared to control plant. Electrophoretic mobility shift assay (EMSA) and Chromatin immunoprecipitation (ChIP) analysis confirmed that SlHY5 and SlPIF3 bind to the promoter of target genes of GLYCOALKALOID METABOLISM (GAME1, GAME4, GAME17), affecting the steady-state concentrations of transcripts coding for SGA pathway enzymes. The results indicate that light-signaling transcription factors HY5 and PIF3 regulate the abundance of SGAs by modulating the transcript levels of these GAME genes. This insight into the regulation of SGA biosynthesis can be used for manipulating the level of these metabolites in crops.

No abstract

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases of wheat in China. Conjunction area of Gansu, Sichuan and Shaanxi, acting as over-summering and over-wintering regions for the pathogen, plays a unique and critical role in epidemics of this disease in China. Because of the complexity in terrains and environmental conditions within this conjunction area, studies on the population structure, gene flow between local subpopulations and maintenance of genetic structure over time within this area are important to understand the epidemiology of this disease in China, and have practical significance in management of this disease at national scale. In this study, 461 isolates of Pst were collected from the junction area of Gansu, Sichuan and Shaanxi from 2013 spring to 2014 spring, and genotyped with amplified fragment length polymorphism markers. Results revealed that genotypic and genetic diversity were consistently high in Gansu and Shaanxi, but low in Sichuan, and a closer genetic relationship was found between Gansu and Sichuan than between them and Shaanxi illustrated by φpt, shared genotypes, Bayesian and nonparametric clustering methods. Genetic differentiation existed among autumn subpopulations, and genetic barriers were detected, although spring subpopulations were less differentiated. Subpopulations in Gangu of Gansu and Longxian of Shaanxi remained stable over the seasons studied. Potential migration events occurred at the junction area between successive seasons. The estimated frequency of sexual reproduction was 0.970 (s) (i.e. 97% of individuals being sexually derived during the yearly sexual cycle), suggesting the existence of sexual reproduction in this region. The main conclusions of this study are that genetic barriers exist at the junction area, and subpopulations in Gansu and Shaanxi are stable, and population exchange occurs mainly between Gansu and Sichuan.

Glycoalkaloids are toxic compounds that are synthesized by many Solanum species. Glycoalkaloid biosynthesis is influenced by plant genetic and environmental conditions. Although many studies have shown that light is an important factor affecting glycoalkaloid biosynthesis, the specific mechanism is currently unknown. Chlorophyll and carotenoid biosynthesis depend on light signal transduction and share some intermediate metabolites with the glycoalkaloid biosynthetic pathway. Here, we used virus-induced gene silencing to silence genes encoding phytoene desaturase (PDS) and magnesium chelatase (CHLI and CHLH) to reduce chlorophyll and carotenoid levels in eggplant leaves. Quantification of carotenoid and chlorophyll levels is analyzed by LC/PDA/APCI/MS and semipolar metabolite profiling by LC/HESI/MS. Notably, the resulting lines showed decreases in glycoalkaloid production. We further found that the expression of some genes involved in the production of glycoalkaloids and other metabolites were suppressed in these silenced lines. Our results indicate that photosynthetic pigment accumulation affects steroidal glycoalkaloid biosynthesis in eggplant leaves. This finding lays the foundation for reducing the levels of endogenous antinutritional compounds in crops.