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SlARF10 plays an important role in the chlorophyll accumulation and photosynthesis of tomato plants, and regulation of its expression affects the starch, fructose, and sucrose content of fruit. Abstract The photosynthesis of green tomatoes contributes to fruit growth and carbon economy. The tomato auxin response factor 10 (SlARF10) belongs to the ARF family and is located in nucleus. In this study, we found that SlARF10 was highly expressed in green fruit. Overexpression of SlARF10 in fruit produced a dark-green phenotype whilst knock-down by RNAi produced a light-green phenotype. Autofluorescence and chlorophyll content analyses confirmed the phenotypes, which indicated that SlARF10 plays an important role in chlorophyll accumulation. Overexpression of SlARF10 positively affected photosynthesis in both leaves and fruit. Furthermore, SlARF10-overexpression lines displayed improved accumulation of starch, fructose, and sucrose in fruit, whilst SlARF10-RNAi lines showed decreased accumulation of starch and sucrose. Regulation of SlARF10 expression altered the expression of AGPase starch biosynthesis genes. SlARF10 positively regulated the expression of SlGLK1, POR, CBP1, and CBP2, which are related to chlorophyll metabolism and regulation. Electrophoretic mobility shift assays confirmed that SlARF10 directly targets to the SlGLK1 promoter. Our results thus indicate that SlARF10 is involved in chlorophyll accumulation by transcriptional activation of SlGLK1 expression in tomato fruit, and provide insights into the link between auxin signaling, chloroplast activity, and sugar metabolism during tomato fruit development.

Global warming is causing a negative impact on plant growth and adversely impacts on crop yield. MicroRNAs (miRNAs) are critical in regulating the expression of genes involved in plant development as well as defense responses. The effects of miRNAs on heat-stressed warrants further investigation. Heat stress increased the expression of miR160 and its precursors but considerably reduced that of its targets, , and . To study the roles of miR160 during heat stress, transgenic plants overexpressing a (160OE) and artificial miR160 (MIM160), which mimics an inhibitor of miR160, were created. T-DNA insertion mutants of miR160 targets were also used to examine their tolerances to heat stress. Results presented that overexpressing miR160 improved seed germination and seedling survival under heat stress. The lengths of hypocotyl elongation and rachis were also longer in 160OE than the wild-type (WT) plants under heat stress. Interestingly, MIM160 plants showed worse adaption to heat. In addition, , and mutants presented similar phenotypes to 160OE under heat stress to advance abilities of thermotolerance. Moreover, transcriptome and qRT-PCR analyses revealed that , and expression levels were regulated by heat in 160OE, MIM160, , and plants. Hence, miR160 altered the expression of the heat shock proteins and plant development to allow plants to survive heat stress.

In Arabidopsis thaliana (Arabidopsis), microRNA160 (miR160) regulates the expression of AUXIN RESPONSE FACTOR10 (ARF10), ARF16 and ARF17 throughout development, including the development of the root system. We have previously shown that in addition to DOUBLE-STRANDED RNA BINDING1 (DRB1), DRB2 is also involved in controlling the rate of production of specific miRNA cohorts in the tissues where DRB2 is expressed in wild-type Arabidopsis plants. In this study, a miR160 overexpression transgene (MIR160B) and miR160-resistant transgene versions of ARF10 and ARF16 (mARF10 and mARF16) were introduced into wild-type Arabidopsis plants and the drb1 and drb2 single mutants to determine the degree of requirement of DRB2 to regulate the miR160 expression module as part of root development. Via this molecular modification approach, we show that in addition to DRB1, DRB2 is required to regulate the level of miR160 production from its precursor transcripts in Arabidopsis roots. Furthermore, we go on to correlate the altered abundance of miR160 or its ARF10, ARF16 and ARF17 target genes in the generated series of transformant lines with the enhanced development of the root system displayed by these plant lines. More specifically, promotion of primary root elongation likely stemmed from enhancement of miR160-directed ARF17 expression repression, while the promotion of lateral and adventitious root formation was the result of an elevated degree of miR160-directed regulation of ARF17 expression, and to a lesser degree, ARF10 and ARF16 expression. Taken together, the results presented in this study identify the requirement of the functional interplay between DRB1 and DRB2 to tightly control the rate of miR160 production, to in turn ensure the appropriate degree of miR160-directed ARF10, ARF16 and ARF17 gene expression regulation as part of normal root system development in Arabidopsis.

Solanum lycopersicum auxin response factor 10 ( SlARF10 ) is post-transcriptionally regulated by Sl-miR160 . Overexpression of a Sl-miR160 -resistant SlARF10 ( mSlARF10 ) resulted in narrower leaflet blades with larger stomata but lower densities. 35S:mSlARF10-6 plants with narrower excised leaves had greater water loss, which was in contrast to the wild type (WT). Further analysis revealed that the actual water loss was not consistent with the calculated stomatal water loss in 35S: mSlARF10-6 and the WT under the dehydration treatment, indicating that there is a difference in hydraulic conductance. Pretreatment with abscisic acid (ABA) and HgCl 2 confirmed higher hydraulic conductance in 35S:mSlARF10 , which is related to the larger stomatal size and higher activity of aquaporins (AQPs). Under ABA treatment, 35S:mSlARF10-6 showed greater sensitivity, and the stomata closed rapidly. Screening by RNA sequencing revealed that five AQP-related genes, fourteen ABA biosynthesis/signal genes and three stomatal development genes were significantly altered in 35S:mSlARF10-6 plants, and this result was verified by qRT-PCR. The promoter analysis showed that upregulated AQPs contain AuxRE and ABRE, implying that these elements may be responsible for the high expression levels of AQPs in 35S:mSlARF10-6 . The three most upregulated AQPs ( SlTIP1-1-like, SlPIP2;4 and SlNIP-type-like ) were chosen to confirm AuxRE and ABRE function. Promoters transient expression demonstrated that the SlPIP2;4 and SlNIP-type-like AuxREs and SlPIP2;4 and SlTIP1-1-like ABREs could significantly enhance the expression of the GUS reporter in 35S:mSlARF10-6 , confirming that AuxRE and ABRE may be the main factors inducing the expression of AQPs. Additionally, two upregulated transcription factors in 35S:mSlARF10-6, SlARF10 and SlABI5-like were shown to directly bind to those elements in an electromobility shift assay and a yeast one-hybrid assay. Furthermore, transient expression of down-regulated ARF10 or up-regulated ABI5 in tomato leaves demonstrated that ARF10 is the direct factor for inducing the water loss in 35S:mSlARF10-6 . Here, we show that although SlARF10 increased the ABA synthesis/signal response by regulating stomatal aperture to mitigate water loss, SlARF10 also influenced stomatal development and AQP expression to affect water transport, and both act cooperatively to control the loss of leaf water in tomato. Therefore, this study uncovers a previously unrecognized leaf water loss regulatory factor and a network for coordinating auxin and ABA signalling in this important process. In an evolutionary context, miR160 regulates ARF10 to maintain the water balance in the leaf, thus ensuring normal plant development and environmental adaptation.

Auxin response factors (ARFs) are plant transcription factors that activate or repress the expression of auxin-responsive genes and accordingly, play key roles in auxin-mediated developmental processes. Here we identified and characterized the Solanum lycopersicum (tomato) ARF10 homolog ( SlARF10 ), demonstrated that it is post-transcriptionally regulated by Sl - miR160 , and investigated the significance of this regulation for tomato development. In wild-type tomato, SlARF10 is primarily expressed in the pericarp of mature and ripened fruit, showing an expression profile complementary to that of Sl - miR160 . Constitutive expression of wild-type SlARF10 did not alter tomato development. However, transgenic tomato plants that constitutively expressed the Sl-miR160a-resistant version ( mSlARF10 ) developed narrow leaflet blades, sepals and petals, and abnormally shaped fruit. During compound leaf development, mSlARF10 accumulation specifically inhibited leaflet blade outgrowth without affecting other auxin-driven processes such as leaflet initiation and lobe formation. Moreover, blade size was inversely correlated with mSlARF10 transcript levels, strongly implying that the SlARF10 protein, which was localized to the nucleus, can function as a transcriptional repressor of leaflet lamina outgrowth. Accordingly, known auxin-responsive genes, which promote cell growth, were downregulated in shoot apices that accumulated increased mSlARF10 levels. Taken together, we propose that repression of SlARF10 by Sl - miR160 is essential for auxin-mediated blade outgrowth and early fruit development.

DOUBLE-STRANDED RNA BINDING (DRB) proteins DRB1, DRB2, and DRB4 are essential for microRNA (miRNA) production in Arabidopsis thaliana (Arabidopsis) with miR160, and its target genes, AUXIN RESPONSE FACTOR10 (ARF10), ARF16, and ARF17, forming an auxin responsive miRNA expression module crucial for root development. Methods: Wild-type Arabidopsis plants (Columbia-0 (Col-0)) and the drb1, drb2, and drb12 mutants were treated with the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), and the miR160-mediated response of these four Arabidopsis lines was phenotypically and molecularly characterized. Results: In 2,4-D-treated Col-0, drb1 and drb2 plants, altered miR160 abundance and ARF10, ARF16, and ARF17 gene expression were associated with altered root system development. However, miR160-directed molecular responses to treatment with 2,4-D was largely defective in the drb12 double mutant. In addition, via profiling of molecular components of the miR160 expression module in the roots of the drb4, drb14, and drb24 mutants, we uncovered a previously unknown role for DRB4 in regulating miR160 production. Conclusions: The miR160 expression module forms a central component of the molecular and phenotypic response of Arabidopsis plants to exogenous auxin treatment. Furthermore, DRB1, DRB2, and DRB4 are all required in Arabidopsis roots to control miR160 production, and subsequently, to appropriately regulate ARF10, ARF16, and ARF17 target gene expression.