Folate shapes plant root architecture by affecting auxin distribution.

Folate (vitamin B9) is important for plant root development, but the mechanism is largely unknown. Here we characterized a root defective mutant, folb2, in Arabidopsis, which has severe developmental defects in the primary root. The root apical meristem of the folb2 mutant is impaired, and adventitious roots are frequently found at the root-hypocotyl junction. Positional cloning revealed that a 61-bp deletion is present in the predicted junction region of the promoter and the 5' untranslated region of AtFolB2, a gene encoding a dihydroneopterin aldolase that functions in folate biosynthesis. This mutation leads to a significant reduction in the transcript level of AtFolB2. Liquid chromatography-mass spectrometry analysis showed that the contents of the selected folate compounds were decreased in folb2. Arabidopsis AtFolB2 knockdown lines phenocopy the folb2 mutant. On the other hand, the application of exogenous 5-formyltetrahydrofolic acid could rescue the root phenotype of folb2, indicating that the root phenotype is indeed related to the folate level. Further analysis revealed that folate could promote rootward auxin transport through auxin transporters and that folate may affect particular auxin/indole-3-acetic acid proteins and auxin response factors. Our findings provide new insights into the important role of folic acid in shaping root structure.

Transcript-wide identification and expression pattern analysis to comprehend the roles of AP2/ERF genes under development and abiotic stress in Trichosanthes kirilowii.

BACKGROUND: The APETALA 2/ ethylene-responsive element binding factors (AP2/ERF), are thought to be associated with plant abiotic stress response, and involved in some plant hormone signaling pathways. Trichosanthes kirilowii is an important edible and medicinal crop, so far no research has been conducted on the TkAP2/ERF genes. RESULT: In this study, a total of 135 TkERFs were identified, these genes were divided into 4 subfamilies and clustered into 13 groups. Moreover, 37 paralogous pairs were identified, with only two having Ka/Ks values greater than 1, proving that most TkERF genes underwent purifying selection during evolution. Co-expression networks constructed using transcriptome data at various flowering stages revealed that 50, 64, and 67 AP2/ERF genes correlated with members of the ethylene, gibberellin, and abscisic acid signaling pathways, respectively. When tissue cultured seedlings were treated with ETH, GA3 and ABA, 11, 12 and 17 genes were found to be up-regulated, respectively, suggesting that some members of the TkERF gene family may be involved in plant hormone signaling pathways. And under 4 ℃, PEG and NaCl treatment, 15, 20 and 19 genes were up-regulated, respectively, this suggested that these selected genes might be involved in plant abiotic stresses. CONCLUSIONS: Overall, we identified 135 AP2/ERF family members, a comprehensive analysis of AP2/ERF gene expression patterns by RNA-seq and qRT-PCR showed that they played important roles in flower development and abiotic stress. This study provided a theoretical basis for the functional study of TkAP2/ERF genes and the genetic improvement of T. kirilowii.

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

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.

SlZF3 regulates tomato plant height by directly repressing SlGA20ox4 in the gibberellic acid biosynthesis pathway.

Plant height is an important target trait for crop genetic improvement. Our previous work has identified a salt-tolerant C2H2 zinc finger, SlZF3, and its overexpression lines also showed a semi-dwarf phenotype, but the molecular mechanism remains to be elucidated. Here, we characterized the dwarf phenotype in detail. The dwarfism is caused by a decrease in stem internode cell elongation and deficiency of bioactive gibberellic acids (GAs), and can be rescued by exogenous GA3 treatment. Gene expression assays detected reduced expression of genes in the GA biosynthesis pathway of the overexpression lines, including SlGA20ox4. Several protein-DNA interaction methods confirmed that SlZF3 can directly bind to the SlGA20ox4 promoter and inhibit its expression, and the interaction can also occur for SlKS and SlKO. Overexpression of SlGA20ox4 in the SlZF3-overexpressing line can recover the dwarf phenotype. Therefore, SlZF3 regulates plant height by directly repressing genes in the tomato GA biosynthesis pathway.

Impairment of hormone pathways results in a general disturbance of fruit primary metabolism in tomato.

Fruit metabolites are regulated by different phytohormones; however, this needs to be investigated. Dynamic metabolite profiling, based on gas chromatography-mass spectrometry, has been conducted on the fruit of tomato cultivar Micro-Tom and its five hormone mutants: dpy, not, dgt, epi and pro. In total, 48 metabolites were quantified, including sugars, organic acids and amino acids. The results demonstrated that ABA had a greater effect on the regulation of primary metabolism in tomato fruit, while ethylene can play an important role in the transition of primary to secondary metabolism. Besides, results from enzyme activities and transcript abundance involved in primary metabolism suggested that AIV and HXK4 could play key roles in the accumulation of the main sugars. To the best of our knowledge, this is the first comprehensive analysis of the link between hormone and metabolite change during fruit development in a collection of mutants with diverse hormone pathways.

Genomic Organization, Phylogenetic and Expression Analysis of the B-BOX Gene Family in Tomato.

The B-BOX (BBX) proteins encode a class of zinc-finger transcription factors possessing one or two B-BOX domains and in some cases an additional CCT (CO, CO-like and TOC1) motif, which play important roles in regulating plant growth, development and stress response. Nevertheless, no systematic study of BBX genes has undertaken in tomato (Solanum lycopersicum). Here we present the results of a genome-wide analysis of the 29 BBX genes in this important vegetable species. Their structures, conserved domains, phylogenetic relationships, subcellular localizations, and promoter cis-regulatory elements were analyzed; their tissue expression profiles and expression patterns under various hormones and stress treatments were also investigated in detail. Tomato BBX genes can be divided into five subfamilies, and twelve of them were found to be segmentally duplicated. Real-time quantitative PCR analysis showed that most BBX genes exhibited different temporal and spatial expression patterns. The expression of most BBX genes can be induced by drought, polyethylene glycol-6000 or heat stress. Some BBX genes were induced strongly by phytohormones such as abscisic acid, gibberellic acid, or ethephon. The majority of tomato BBX proteins was predicted to be located in nuclei, and the transient expression assay using Arabidopsis mesophyll protoplasts demonstrated that all the seven BBX members tested (SlBBX5, 7, 15, 17, 20, 22, and 24) were localized in nucleus. Our analysis of tomato BBX genes on the genome scale would provide valuable information for future functional characterization of specific genes in this family.

The mechanism underlying fast germination of tomato cultivar LA2711.

Seed germination is important for early plant morphogenesis as well as abiotic stress tolerance, and is mainly controlled by the phytohormones abscisic acid (ABA) and gibberellic acid (GA). Our previous studies identified a salt-tolerant tomato cultivar, LA2711, which is also a fast-germinating genotype, compared to its salt-sensitive counterpart, ZS-5. In an effort to further clarify the mechanism underlying this phenomenon, we compared the dynamic levels of ABA and GA4, the transcript abundance of genes involved in their biosynthesis and catabolism as well as signal transduction between the two cultivars. In addition, we tested seed germination sensitivity to ABA and GAs. Our results revealed that insensitivity of seed germination to exogenous ABA and low ABA content in seeds are the physiological mechanisms conferring faster germination rates of LA2711 seeds. SlCYP707A2, which encodes an ABA catabolic enzyme, may play a decisive role in the fast germination rate of LA2711, as it showed a significantly higher level of expression in LA2711 than ZS-5 at most time points tested during germination. The current results will enable us to gain insight into the mechanism(s) regarding seed germination of tomato and the role of fast germination in stress tolerance.