Heat-inducible SlWRKY3 confers thermotolerance by activating the SlGRXS1 gene cluster in tomato

High temperature stress is one of the major environmental factors that affect the growth and development of plants. Although WRKY transcription factors play a critical role in stress responses, there are few studies on the regulation of heat stress by WRKY transcription factors,especially in tomato. Here, we identified a group I WRKY transcription factor, SlWRKY3, involved in thermotolerance in tomato. First, SlWRKY3 was induced and upregulated under heat stress. Accordingly, overexpression of SlWRKY3 led to an increase, whereas knock-out of SlWRKY3 resulted in decreased tolerance to heat stress. Overexpression of SlWRKY3 accumulated less reactive oxygen species(ROS), whereas knock-out of SlWRKY3 accumulated more ROS under heat stress. This indicated that SlWRKY3 positively regulates heat stress in tomato. In addition,SlWRKY3 activated the expression of a range of abiotic stress-responsive genes involved in ROS scavenging, such as a SlGRXS1 gene cluster.Further analysis showed that SlWRKY3 can bind to the promoters of the SlGRXS1 gene cluster and activate their expression. Collectively, these results imply that SlWRKY3 is a positive regulator of thermotolerance through direct binding to the promoters of the SlGRXS1 gene cluster and activating their expression and ROS scavenging.

Multiple-model GWAS identifies optimal allelic combinations of quantitative trait loci for malic acid in tomato

Malic acid(MA)is an important flavor acid in fruits and acts as a mediator in a series of metabolic pathways.It is important to understand the factors affecting MA metabolism for fruit flavor improvement and to understand MA-mediated biological processes.However,themetabolic accumulation of MA is controlled by complex heredity and environmental factors,making it difficult to predict and regulate the metabolism of MA.In this study,we carried out a genome-wide association study(GWAS)on MA using eight milestone models with two-environment repeats.A series of associated SNP variations were identified from the GWAS,and 15 high-confidence annotated geneswere further predicted based on linkage disequilibrium and lead SNPs.The transcriptome data of candidate geneswere explored within different tomato organs as well as various fruit tissues,and suggested specific expression patterns in fruit pericarp.Based on the genetic parameters of population differentiation and SNP distribution,tomato MA content has been more influenced by domestication sweeps and less affected by improvement sweeps in the long-term history of tomato breeding.In addition,genotype×environment interaction might contribute to the difference in domestication phenotypic data under different environments.This study provides new genetic insights into how tomato changed its MA content during breeding and makes available function-based markers for breeding by marker-assisted selection.

VG,encoding a thylakoid formation protein,regulates the formation of variegated leaves in tomato

Leaf-color mutations have been studied extensively in plants.However,to better understand the complex mechanisms underlying the formation of leaf color,it is essential to continue discover novel genes involved in the process of leaf color development.In this study,we identified a variegated-leaf(vg)mutant in tomato that exhibited defective phenotypes in thylakoids and photosynthesis.To clone the vg locus,an F2population was constructed from the cross between the vg mutant(Solanum lycopersicum)and the wild tomato LA1589(S.pimpinellifolium).Using the map-based cloning approach,the vg locus was mapped on chromosome 7 and narrowed down to a 128 kb region that contained 21 open reading frames(ORFs).The expression levels of ORF9,ORF10,and ORF13 were significantly lower in vg than in the wild-type plants,while the ORF11 transcript level was elevated in vg.We then mutagenized ORF9,ORF10,and ORF13 by the CRISPR/Cas9 system in the wild-type tomato background and found that only the ORF10 mutation reproduced the phenotype of variegated leaves,indicating that ORF10 represents VG and its down-regulated expression was responsible for the variegated leaf phenotype.ORF10 encodes a thylakoid formation protein and its mutant lines showed reduced levels of chlorophyll synthesis and photosynthesis.Taken together,these results suggest that VG is necessary for chloroplast development,chlorophyll synthesis,and photosynthesis in tomato.

Interactions between ShPP2-1, an F-box family gene, and ACR11A regulate cold toleranee of tomato

There is a critical need to identify germplasm resources and genes that promote cold tolerance of tomato because global tomato production is threatened by cold stress.We found that the expression of an F-box gene family member named ShPP2-1 from Solanum habrochaites is cold inducible and studied its contribution to cold tolerance.Overexpression of ShPP2-1 in cultivated tomato(AC)reduced cold tolerance by intensifying damage to cell membranes.To explore the underlying molecular mechanism,we conducted a yeast two-hybrid library screen and found that a protein containing ACT domain repeats named ACR11A interacts with PP2-1.Overexpression of SIACR11A in AC enhanced the cold tolerance of seedlings and germinating seeds.Cold tolerance decreased in tomato plants that overexpressed both of these genes.Additionally,we performed seed germination experiments in the cold with 177 tomato accessions and identified two alleles of SlACR11A that differ in one single-nucleotide polymorphism.We found that one of these alleles,SlACR11A G,is significantly enriched in cold-tolerant tomato plants.Taken together,our fi ndings indicate that the combination of low expression levels of PP2-1 and high expression levels of ACR11A can promote cold tolerance.These genes may therefore serve as direct targets for both genetic engineering and improvement projects that aim to enhance the cold tolerance of tomato.

Effect of shading on ascorbic acid accumulation and biosynthetic gene expression during tomato fruit development and ripening

The purpose of the current study was to determine the effect of leaf shading,fruit shading,and a combination of both,on the accumulation of ascorbic acid(AsA)and the expression levels of AsA biosynthetic genes at the immature green,mature green,breaker,and red ripe stages of Ailsa craig tomato during fruit development.Shading(72%reducing of light intensity)imposed on the leaves significantly reduced AsA content and AsA biosynthetic gene expression in the fruits.Leaf shading,fruit shading,and a combination of both significantly decreased the amount of total AsA and reduced AsA to a range of 18.5%−31.5%at mature green,breaker,and red ripe stages of tomato fruits,with no significant change at the immature green stage of fruits.Moreover,reducing the light intensity in tomato leaves,fruits or both resulted in reduced expression of most AsA biosynthetic genes in the fruits,except for PMM,cAPX,tAPX,and APX7 genes under leaf shading,GPI,PMI,PMM,GP1,GP2,cAPX,and tAPX genes under fruit shading,and PMM,cAPX,APX1,and APX7 genes under both shading.The expression level of GMP,GP1,and GalDH showed an upregulation at the red ripe stage in fruits with leaf shading,and also an up-regulation at the immature green and red ripe stages with both shading.Furthermore,positive correlations between expression of AsA biosynthetic genes and AsA accumulation were recorded under leaf shading,fruit shading,and both types of shading,while a negative correlation was recorded under normal conditions without shading.

Regulation of invertase and sucrose for improving tomato fruit flavor:A review

Tomato(Solanum lycopersicum L.)is a commercially farmed vegetable belonging to the Solanaceae family,the third most important vegetable after potato(Solanum tuberosum L.)and onion(Allium cepa L.).It is cultivated for its fresh fruits and processed paste,with over 153 million metric tons of global production.However,modern tomato cultivars have limited sugars,acids,and volatiles allelic diversity as flavor has generally been less prioritized in breeding programs.Invertase is an essential regulator of flavor and sugar metabolism in tomato.Genetic control of tomato flavor is still incomplete without a clear understanding of the roles of invertase and sucrose metabolism.This review provides an overview of our current understanding of the invertase mode of action in sucrose metabolism,their evolutionary and functional divergence in the tomato genome,role in stress response,genetic and hormonal control of fruit flavor and quality.We summarized the primary roles of invertase in sugar metabolism and fruit flavor.