Yongfeng Gao

A Role of Tomato UV-Damaged DNA Binding Protein 1 (DDB1) in Organ Size Control via an Epigenetic Manner

Epigenetic modification generally refers to phenotypic changes by a mechanism other than changes in DNA sequence and plays a significant role in developmental processes. In this study, we found that overexpression of one alternatively spliced tomato DDB1 transcript, DDB1F that is prevalently present in all tested tissues, resulted in reduction of organ size. Transgenic plants constitutively expressing the DDB1F from a strong cauliflower mosaic virus (CaMV) 35S promoter displayed moderately reduced size in vegetative organs (leaves and stems) and radically decreased size in reproductive organs (flowers, seeds and fruits), in which several genes encoding negative regulators for cell division were upregulated. Significantly, reduction of organ size conferred by overexpression of DDB1F transgene appears not to segregate in the subsequent generations, suggesting the phenotypic alternations are manipulated in an epigenetic manner and can be transmitted over generations. This notion was further substantiated by analysis of DNA methylation level at the SlWEE1 gene (encoding a negative regulator of cell division), revealing a correlation between less methylation in the promoter region and elevated expression level of this gene. Thus, our results suggest DDB1 plays an important role in regulation of the epigenetic state of genes involved in organogenesis, despite the underlying mechanism remains to be elucidated.

Functional characterization of two alternatively spliced transcripts of tomato ABSCISIC ACID INSENSITIVE3 ( ABI3 ) gene

Alternative splicing can produce transcripts that encode proteins with altered functions. The transcripts of the ABSCISIC ACID INSENSITIVE3 (ABI3)/VIVIPAROUS1 (VP1) gene, which is an important component in abscisic acid (ABA) signaling, are subjected to alternative splicing in both monocotyledons and dicotyledons. We identified two alternatively spliced tomato (Solanumlycopersicum) SlABI3 transcripts, SlABI3-F and SlABI3-T, which encode the nucleus-localized full-length and truncated proteins, respectively. The tissue-specific accumulation of SlABI3-F and SlABI3-T was determined, particularly in seeds at different developmental stages and in response to phytohormonal and abiotic stress. Ectopic over-expression of SlABI3-F and SlABI3-T resulted in the induction of seed-specific genes SlSOM, SlEM1 and SlEM6 in vegetative tissues. However, over-expression of SlABI3-F, but not SlABI3-T, activated expression of the downstream gene SlABI5 and conferred hypersensitivity to exogenous ABA during seed germination and primary root growth. In addition, the SlABI3-F protein interacted with SlABI5 much stronger than SlABI3-T did in the yeast two-hybrid assay. These results suggest that SlABI3-F and SlABI3-T have similar and distinct functionality in the ABA signaling, dependent on which tissue/organ they accumulate in.

Over-expression of SlWRKY39 leads to enhanced resistance to multiple stress factors in tomato

The WRKY transcription factors are one of the well-characterized classes of plant transcription factors, which participated in various biotic and abiotc stress responses. Previous study showed that there are 81 WRKY genes in tomato, wherein a number of SlWRKY genes including SlWRKY39 were significantly up-regulated under salt, drought stress and PstDC3000 infection. However little is known about their physiological role in tomato. In this study, by using a forward genetic approach, we demonstrated transgenic plants over-expressing SlWRKY39 showing enhanced resistance to multiple stress factors including PstDC3000, salt and drought. Transgenic plants accumulated higher level of proline and lower level of malonic dialdehyde. Compared with wild type, the expression of pathogenesis-related genes SlPR1, SlPR1a1 and environmental stress related genes SlRD22, SlDREB2A were up-regulated in the transgenic plants. These results indicated that SlWRKY39 is a positive regulatory component of tomato against biotic and abiotic stress probably via activating the expression of both pathogenesis-related genes and stress related genes.

SISOM inhibits seed germination by regulating the expression of ABA/GA metabolic genes and SIABI5 in Solanum lycopersicum

SOM encodes a nucleus-localized CCCH-type zinc finger protein and negatively regulates seed germination in Arabidopsis thaliana. We have previously demonstrated that ectopic expression of SIABI3, an important transcription factor in abscisic acid (ABA) signaling pathway, resulted in alteration of SISOM expression patterns in both leaf and seed of tomato. In this study, we aimed to elucidate the function of tomato SISOM in regarding to seed germination and seedling development. Here, we constructed SISOM over-expression vector pBI121-SOM driven by CaMV 35S promoter, and the recombinant plasmid was incorporated into wild-type tomato by the method of Agrobacterium tumefaciens-mediated transformation. The result showed that over-expression of SISOM conferred enhanced responses to exogenous ABA application during seed germination and seedling development. In addition, ectopic expression of SISOM resulted in the alteration of expression level of ABA/GA (gibberellins) metabolic genes, such as SIABA1, SlCYP707A1, SlGA3ox2, and SIGA2ox4, in both leaf and seed. The ABA anabolic gene SIABA1 and the GA catabolic gene SIGA2ox4 were up-regulated while the ABA catabolic gene SICYP707A1 and the GA anabolic gene SIGA3ox2 were down-regulated. Compared to wild type, the expression level of SIABI5 was increased by about 40–50% in transgenic seeds while adding exogenous ABA treatment. These results support the notion that SISOM inhibits seed germination by regulating ABA/GA metabolic genes and SIABI5 expression in Solanum lycopersicum.

Tomato UV-B receptor SlUVR8 mediates plant acclimation to UV-B radiation and enhances fruit chloroplast development via regulating SlGLK2

Plants utilize energy from sunlight to perform photosynthesis in chloroplast, an organelle that could be damaged by solar UV radiation. The ultraviolet-B (UV-B) photoreceptor UVR8 is required for UV-B perception and signal transduction. However, little is known about how UVR8 influence chloroplast development under UV-B radiation. Here, we characterized tomato UVR8 gene (SlUVR8) and our results indicated that SlUVR8 facilitate plant acclimation to UV-B stress by orchestrating expression of the UVB-responsive genes (HY5 and CHS) and accumulating UV-absorptive compounds. In addition, we also discovered that SlUVR8 promotes fruit chloroplast development through enhancing accumulation of transcription factor GOLDEN2-LIKE2 (SlGLK2) which determines chloroplast and chlorophyll levels. Furthermore, UV-B radiation could increase expression of SlGLK2 and its target genes in fruits and leaves. SlUVR8 is required for UVB-induced SlGLK2 expression. Together, our work not only identified the conserved functions of SlUVR8 gene in response to UV-B stress, but also uncovered a novel role that SlUVR8 could boost chloroplast development by accumulating SlGLK2 proteins.