Yongen Lu

A regulatory gene induces trichome formation and embryo lethality in tomato

Trichomes are universal biological structures originating from the aerial epidermis, which serve as an excellent model to study plant differentiation at the cell level. Although the pathway regulating trichome formation in the Rosids has been well characterized, only very recently a few genes were identified for trichome initiation in the Asterids. In this study, we cloned Woolly (Wo), essential for trichome formation in tomato. Transgenic experiments revealed that the woolly phenotype is caused by the mutation in Wo which encodes a homeodomain protein containing a bZIP motif and a START domain. We identified three alleles of Wo and found that each allele contains a missense mutation, which respectively results in an amino acid substitution at the C terminus. Microarray and expression analysis showed that the expression of a B-type cyclin gene, SlCycB2, is possibly regulated by Wo, which also participates in trichome formation. Suppression of Wo or SlCycB2 expression by RNAi decreased the number of type I trichomes, and direct protein–protein interaction was detected between them, implying that both proteins may work together in the regulation of this type of trichome formation. Cytological observation and Wo transcript analysis in the developing seeds showed that embryo development was also correlated with Wo.

SpUSP, an annexin-interacting universal stress protein, enhances drought tolerance in tomato

Universal stress protein (USP) appears to play an active role in the abiotic stress response, but their functions remain largely unknown in plants. A USP gene (SpUSP) was cloned from wild tomato (Solanum pennellii) and functionally characterized in cultivated tomato in the present study. The SpUSP transcript is abundantly accumulated in leaf stomata and its expression varied with the circadian rhythm. SpUSP was remarkably induced by dehydration, salt stress, oxidative stress, and the phytohormone abscisic acid (ABA) etc. This protein was predominantly localized in the nucleus and cell membrane. Overexpressing SpUSP increased drought tolerance of tomato in the seedling and adult stages. Under drought stress, the ABA content significantly increased in the SpUSP-overexpressing plants, which induced stomatal closure and reduced water loss, leading to the enhancement of drought tolerance. Based on the microarray data, a large number of chlorophyll a/b-binding proteins and photosystem-related genes were up-regulated in the SpUSP-overexpressing plants under drought conditions, which possibly enhanced the stomatal sensivitity to ABA and maintained the photosynthetic function. SpUSP overexpression also alleviated the oxidative damage accompanied by oxidative stress-responsive gene activation and osmolyte accumulation. Annexin (SGN-U314161) was found to interacte with SpUSP in the yeast two-hybrid method. This interaction was further confirmed by the bimolecular fluorescence complementation assay. The present study demonstrated that the annexin-interacting SpUSP plays important roles in the drought tolerance of tomato by influencing ABA-induced stomatal movement, increasing photosynthesis, and alleviating oxidative stress.

Genomic organization, phylogenetic comparison and expression profiles of annexin gene family in tomato (Solanum lycopersicum)

Annexins have been suggested to play pivotal roles in stress resistance and plant development. However, related studies on fruit-bearing plants, especially on fruit development, are very limited. In the present study, we provide a comprehensive overview of the annexin family in tomato, describing the gene structure, promoter cis-regulatory elements, organ expression profile, and gene expression patterns under hormone and stress treatments. Bioinformatic analysis revealed that the nine tomato annexins were structurally different from their animal counterparts, but highly conserved annexin domains were still found in most of them. Cis-regulatory element prediction showed that there were important elements in the 2kb upstream promoter regions, including stress- and hormone-responsive-related elements. The expression patterns of these genes were investigated, and the results revealed that they were regulated under developmental processes and environmental stimuli. Among them, AnnSl1.1 and AnnSl2 were highly expressed in most of the tested organs. Genes preferentially or specifically expressed in organs, such as stigma or ovary (AnnSl6), stamen (AnnSl8), and fruit pericarp (AnnSl1.2 and AnnSl9), were identified. Some annexin genes were induced by plant hormones including abscisic acid (AnnSl3, AnnSl6, AnnSl8, and AnnSl9) and gibberellic acid (AnnSl1.1, AnnSl1.2, AnnSl4, and AnnSl7). Most of these annexin genes were induced by salt, drought, wounding, and heat or cold stresses. The present study provides significant information for understanding the diverse roles of annexins in tomato growth and development.

Genome-Wide Analysis of the Cyclin Gene Family in Tomato

Cyclins play important roles in cell division and cell expansion. They also interact with cyclin-dependent kinases to control cell cycle progression in plants. Our genome-wide analysis identified 52 expressed cyclin genes in tomato. Phylogenetic analysis of the deduced amino sequences of tomato and Arabidopsis cyclin genes divided them into 10 types, A-, B-, C-, D-, H-, L-, T-, U-, SDS- and J18. Pfam analysis indicated that most tomato cyclins contain a cyclin-N domain. C-, H- and J18 types only contain a cyclin-C domain, and U-type cyclins contain another potential cyclin domain. All of the cyclin genes are distributed throughout the tomato genome except for chromosome 8, and 30 of them were found to be segmentally duplicated; they are found on the duplicate segments of chromosome 1, 2, 3, 4, 5, 6, 10, 11 and 12, suggesting that tomato cyclin genes experienced a mass of segmental duplication. Quantitative real-time polymerase chain reaction analysis indicates that the expression patterns of tomato cyclin genes were significantly different in vegetative and reproductive stages. Transcription of most cyclin genes can be enhanced or repressed by exogenous application of gibberellin, which implies that gibberellin maybe a direct regulator of cyclin genes. The study presented here may be useful as a guide for further functional research on tomato cyclins.

Genome-wide identification and expression analysis of the expansin gene family in tomato

Plant expansins are capable of inducing pH-dependent cell wall extension and stress relaxation. They may be useful as targets for crop improvement to enhance fruit development and stress resistance. Tomato is a major agricultural crop and a model plant for studying fruit development. Because only some tomato expansins have been studied, a genome-wide analysis of the tomato expansin family is necessary. In this study, we identified 25 SlEXPAs, eight SlEXPBs, one SlEXLA, four SlEXLBs, and five short homologs in the tomato genome. 25 of these genes were identified as being expressed. Bioinformatic analysis showed that although tomato expansins share similarities with those from other plants, they also exhibit specific features regarding genetic structure and amino acid sequences, which indicates a unique evolutionary process. Segmental and tandem duplication events have played important roles in expanding the tomato expansin family. Additionally, the 3-exon/2-intron structure may form the basic organization of expansin genes. We identified new expansin genes preferentially expressed in fruits (SlEXPA8, SlEXPB8, and SlEXLB1), roots (SlEXPA9, SlEXLB2, and SlEXLB4), and floral organs. Among the analyzed genes those that were inducible by hormone or stress treatments, including SlEXPA3, SlEXPA7, SlEXPB1–B2, SlEXPB8, SlEXLB1–LB2, and SlEXLB4. Our findings may further clarify the biological activities of tomato expansins, especially those related to fruit development and stress resistance, and contribute to the genetic modification of tomato plants to improve crop quality and yield.

The C2H2 zinc-finger protein SlZF3 regulates AsA synthesis and salt tolerance by interacting with CSN5B

Summary Abiotic stresses are a major cause of crop loss. Ascorbic acid (AsA) promotes stress tolerance by scavenging reactive oxygen species (ROS), which accumulate when plants experience abiotic stress. Although the biosynthesis and metabolism of AsA are well established, the genes that regulate these pathways remain largely unexplored. Here, we report on a novel regulatory gene from tomato (Solanum lycopersicum) named SlZF3 that encodes a Cys2/His2‐type zinc‐finger protein with an EAR repression domain. The expression of SlZF3 was rapidly induced by NaCl treatments. The overexpression of SlZF3 significantly increased the levels of AsA in tomato and Arabidopsis. Consequently, the AsA‐mediated ROS‐scavenging capacity of the SlZF3‐overexpressing plants was increased, which enhanced the salt tolerance of these plants. Protein–protein interaction assays demonstrated that SlZF3 directly binds CSN5B, a key component of the COP9 signalosome. This interaction inhibited the binding of CSN5B to VTC1, a GDP‐mannose pyrophosphorylase that contributes to AsA biosynthesis. We found that the EAR domain promoted the stability of SlZF3 but was not required for the interaction between SlZF3 and CSN5B. Our findings indicate that SlZF3 simultaneously promotes the accumulation of AsA and enhances plant salt‐stress tolerance.