The Solanum lycopersicum AUXIN RESPONSE FACTOR 7 (SlARF7) mediates cross-talk between auxin and gibberellin signalling during tomato fruit set and development

New Advances in the Study of Regulation of Tomato Flowering-Related Genes Using Biotechnological Approaches

The tomato is a convenient object for studying reproductive processes, which has become a classic. Such complex processes as flowering and fruit setting require an understanding of the fundamental principles of molecular interaction, the structures of genes and proteins, the construction of signaling pathways for transcription regulation, including the synchronous actions of cis-regulatory elements (promoter and enhancer), trans-regulatory elements (transcription factors and regulatory RNAs), and transposable elements and epigenetic regulators (DNA methylation and acetylation, chromatin structure). Here, we discuss the current state of research on tomatoes (2017-2023) devoted to studying the function of genes that regulate flowering and signal regulation systems using genome-editing technologies, RNA interference gene silencing, and gene overexpression, including heterologous expression. Although the central candidate genes for these regulatory components have been identified, a complete picture of their relationship has yet to be formed. Therefore, this review summarizes the latest achievements related to studying the processes of flowering and fruit set. This work attempts to display the gene interaction scheme to better understand the events under consideration.

Impact of Climate Change on Altered Fruit Quality with Organoleptic, Health Benefit, and Nutritional Attributes

As a consequence of global climate change, acute water deficit conditions, soil salinity, and high temperature have been on the rise in their magnitude and frequency, which have been found to impact plant growth and development negatively. However, recent evidence suggests that many fruit plants that face moderate abiotic stresses can result in beneficial effects on the postharvest storage characters of the fruits. Salinity, drought, and high temperature conditions stimulate the synthesis of abscisic acid (ABA), and secondary metabolites, which are vital for fruit quality. The secondary metabolites like phenolic acids and anthocyanins that accumulate under abiotic stress conditions have antioxidant activity, and therefore, such fruits have health benefits too. It has been noticed that fruits accumulate more sugar and anthocyanins owing to upregulation of phenylpropanoid pathway enzymes. The novel information that has been generated thus far indicates that the growth environment during fruit development influences the quality components of the fruits. But the quality depends on the trade-offs between productivity, plant defense, and the frequency, duration, and intensity of stress. In this review, we capture the current knowledge of the irrigation practices for optimizing fruit production in arid and semiarid regions and enhancement in the quality of fruit with the application of exogenous ABA and identify gaps that exist in our understanding of fruit quality under abiotic stress conditions.

Loss of S-nitrosoglutathione reductase disturbs phytohormone homeostasis and regulates shoot side branching and fruit growth in tomato

S-Nitrosoglutathione plays a central role in nitric oxide (NO) homeostasis, and S-nitrosoglutathione reductase (GSNOR) regulates the cellular levels of S-nitrosoglutathione across kingdoms. Here, we investigated the role of endogenous NO in shaping shoot architecture and controlling fruit set and growth in tomato (Solanum lycopersicum). SlGSNOR silencing promoted shoot side branching and led to reduced fruit size, negatively impacting fruit yield. Greatly intensified in slgsnor knockout plants, these phenotypical changes were virtually unaffected by SlGSNOR overexpression. Silencing or knocking out of SlGSNOR intensified protein tyrosine nitration and S-nitrosation and led to aberrant auxin production and signaling in leaf primordia and fruit-setting ovaries, besides restricting the shoot basipetal polar auxin transport stream. SlGSNOR deficiency triggered extensive transcriptional reprogramming at early fruit development, reducing pericarp cell proliferation due to restrictions on auxin, gibberellin, and cytokinin production and signaling. Abnormal chloroplast development and carbon metabolism were also detected in early-developing NO-overaccumulating fruits, possibly limiting energy supply and building blocks for fruit growth. These findings provide new insights into the mechanisms by which endogenous NO fine-tunes the delicate hormonal network controlling shoot architecture, fruit set, and post-anthesis fruit development, emphasizing the relevance of NO-auxin interaction for plant development and productivity.

Diversity and genetic architecture of agro-morphological traits in a core collection of European traditional tomato

European traditional tomato varieties have been selected by farmers given their consistent performance and adaptation to local growing conditions. Here we developed a multipurpose core collection, comprising 226 accessions representative of the genotypic, phenotypic, and geographical diversity present in European traditional tomatoes, to investigate the basis of their phenotypic variation, gene×environment interactions, and stability for 33 agro-morphological traits. Comparison of the traditional varieties with a modern reference panel revealed that some traditional varieties displayed excellent agronomic performance and high trait stability, as good as or better than that of their modern counterparts. We conducted genome-wide association and genome-wide environment interaction studies and detected 141 quantitative trait loci (QTLs). Out of those, 47 QTLs were associated with the phenotype mean (meanQTLs), 41 with stability (stbQTLs), and 53 QTL-by-environment interactions (QTIs). Most QTLs displayed additive gene actions, with the exception of stbQTLs, which were mostly recessive and overdominant QTLs. Both common and specific loci controlled the phenotype mean and stability variation in traditional tomato; however, a larger proportion of specific QTLs was observed, indicating that the stability gene regulatory model is the predominant one. Developmental genes tended to map close to meanQTLs, while genes involved in stress response, hormone metabolism, and signalling were found within regions affecting stability. A total of 137 marker-trait associations for phenotypic means and stability were novel, and therefore our study enhances the understanding of the genetic basis of valuable agronomic traits and opens up a new avenue for an exploitation of the allelic diversity available within European traditional tomato germplasm.

Parthenocarpy-related genes induced by naphthalene acetic acid in oil palm interspecific O × G [Elaeis oleifera (Kunth) Cortés × Elaeis guineensis Jacq.] hybrids

Parthenocarpy is the development without fertilization of seedless fruits. In the oil palm industry, the development of parthenocarpic fruits is considered an attractive option to increase palm oil production. Previous studies have shown the application of synthetic auxins in Elaeis guineensis, and interspecific O×G hybrids (Elaeis oleifera (Kunth) Cortés × E. guineensis Jacq.) induces parthenocarpy. The aim of this study was to identify the molecular mechanism through transcriptomics and biology system approach to responding to how the application of NAA induces parthenocarpic fruits in oil palm O×G hybrids. The transcriptome changes were studied in three phenological stages (PS) of the inflorescences: i) PS 603, pre-anthesis III, ii) PS 607, anthesis, and iii) PS 700, fertilized female flower. Each PS was treated with NAA, Pollen, and control (any application). The expression profile was studied at three separate times: five minutes (T0), 24 hours (T1), and 48 h post-treatment (T2). The RNA sequencing (RNA seq) approach was used with 27 oil palm O×G hybrids for a total of 81 raw samples. RNA-Seq showed around 445,920 genes. Numerous differentially expressed genes (DEGs) were involved in pollination, flowering, seed development, hormone biosynthesis, and signal transduction. The expression of the most relevant transcription factors (TF) families was variable and dependent on the stage and time post-treatment. In general, NAA treatment expressed differentially more genes than Pollen. Indeed, the gene co-expression network of Pollen was built with fewer nodes than the NAA treatment. The transcriptional profiles of Auxin-responsive protein and Gibberellin-regulated genes involved in parthenocarpy phenomena agreed with those previously reported in other species. The expression of 13 DEGs was validated by RT-qPCR analysis. This detailed knowledge about the molecular mechanisms involved in parthenocarpy could be used to facilitate the future development of genome editing techniques that enable the production of parthenocarpic O×G hybrid cultivars without growth regulator application.

FveARF2 negatively regulates fruit ripening and quality in strawberry

Auxin response factors (ARFs) are transcription factors that play important roles in plants. ARF2 is a member of the ARF family and participates in many plant growth and developmental processes. However, the role of ARF2 in strawberry fruit quality remains unclear. In this study, FveARF2 was isolated from the woodland strawberry 'Ruegen' using reverse transcription-polymerase chain reaction (RT-PCR), which showed that FveARF2 expression levels were higher in the stem than in other organs of the 'Ruegen' strawberry. Moreover, FaARF2 was higher in the white fruit stage of cultivated strawberry fruit than in other stage. Subcellular localization analysis showed that FveARF2 is located in the nucleus, while transcriptional activation assays showed that FveARF2 inhibited transcription in yeast. Silencing FveARF2 in cultivated strawberry fruit revealed earlier coloration and higher soluble solid, sugar, and anthocyanin content in the transgenic fruit than in the control fruit, overexpression of FveARF2 in strawberry fruit delayed ripening and lower soluble solid, sugar, and anthocyanin content compared to the control fruit. Gene expression analysis indicated that the transcription levels of the fruit ripening genes FaSUT1, FaOMT, and FaCHS increased in FveARF2-RNAi fruit and decreased in FveARF2-OE fruit, when compared with the control. Furthermore, yeast one-hybrid (Y1H) and GUS activity experiments showed that FveARF2 can directly bind to the AuxRE (TGTCTC) element in the FaSUT1, FaOMT, and FaCHS promoters in vitro and in vivo. Potassium ion supplementation improved the quality of strawberry fruit, while silencing FveARF2 increased potassium ion content in transgenic fruit. The Y1H and GUS activity experiments also confirmed that FveARF2 could directly bind to the promoter of FveKT12, a potassium transporter gene, and inhibited its expression. Taken together, we found that FveARF2 can negatively regulate strawberry fruit ripening and quality, which provides new insight for further study of the molecular mechanism of strawberry fruit ripening.

Options for the generation of seedless cherry, the ultimate snacking product

This manuscript identifies cherry orthologues of genes implicated in the development of pericarpic fruit and pinpoints potential options and restrictions in the use of these targets for commercial exploitation of parthenocarpic cherry fruit. Cherry fruit contain a large stone and seed, making processing of the fruit laborious and consumption by the consumer challenging, inconvenient to eat 'on the move' and potentially dangerous for children. Availability of fruit lacking the stone and seed would be potentially transformative for the cherry industry, since such fruit would be easier to process and would increase consumer demand because of the potential reduction in costs. This review will explore the background of seedless fruit, in the context of the ambition to produce the first seedless cherry, carry out an in-depth analysis of the current literature around parthenocarpy in fruit, and discuss the available technology and potential for producing seedless cherry fruit as an 'ultimate snacking product' for the twenty-first century.

Cross-talk between the cytokinin, auxin, and gibberellin regulatory networks in determining parthenocarpy in cucumber

Cucumber is a model plant for studying parthenocarpy with abundant slicing- and pickling-type germplasm. This study was undertaken to understand the role of the important cytokines (CKs), auxin (AUX) and gibberellin (GA) biosynthesis and degradation genes for the induction of parthenocarpy in slicing and pickling germplasm. Two genotypes of gynoecious parthenocarpic cucumber, PPC-6 and DG-8, along with an MABC-derived gynoecious non-parthenocarpic line, IMPU-1, were evaluated in this study. The slicing and pickling cucumber genotypes PPC-6 and DG-8 were strongly parthenocarpic in nature and set fruit normally without pollination. Endogenous auxin and gibberellin were significantly higher in parthenocarpic than non-parthenocarpic genotypes, whereas the concentration of cytokinins varied among the genotypes at different developmental stages. However, the exogenous application of Zeatin and IAA + Zeatin was effective in inducing parthenocarpic fruit in IMPU-1. Expression analysis with important CK, AUX, and GA biosynthesis-related genes was conducted in IMPU-1, PPC-6, and DG-8. The expression of the CK synthase, IPT, IPT3, PaO, LOG1, LOG2, CYP735A1, and CYP735A2 was up-regulated in the parthenocarpic genotypes. Among the transcription factor response regulators (RRs), positive regulation of CSRR8/9b, CSRR8/9d, CSRR8/9e, and CSRR16/17 and negative feedback of the CK signalling genes, such as CsRR3/4a, CsRR3/4b, CsRR8/9a, and CsRR8/9c, were recorded in the parthenocarpic lines. Homeostasis between cytokinin biosynthesis and degradation genes such as CK oxidases (CKXs) and CK dehydrogenase resulted in a non-significant difference in the endogenous CK concentration in the parthenocarpic and non-parthenocarpic genotypes. In addition, up-regulation of the key auxin-inducing proteins and GA biosynthesis genes indicated their crucial role in the parthenocarpic fruit set of cucumber. This study establishes the critical role of the CKs, AUX, and GA regulatory networks and their cross-talk in determining parthenocarpy in slicing and pickling cucumber genotypes.

SlMBP22 overexpression in tomato affects flower morphology and fruit development

MADS-domain transcription factors have been identified as key regulators involved in proper flower and fruit development in angiosperms. As members of the MADS-box subfamily, B_sister (B_s) genes have been observed to play an important role during the evolution of the reproductive organs in seed plants. However, their effects on reproductive development in fruit crops, such as tomato (Solanum lycopersicum), remain unclear. Here, we found that SlMBP22 overexpression (SlMBP22-OE) resulted in considerable alterations in floral morphology and affected the expression levels of several floral homeotic genes. Further analysis by yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays demonstrated that SlMBP22 forms dimers with class A protein MACROCALYX (MC) and SEPALLATA (SEP) floral homeotic proteins TM5 and TM29, respectively. In addition, pollen viability and cross-fertilization assays suggested that the defect in female reproductive development was responsible for the infertility phenotype observed in the strong overexpression transgenic plants. Transgenic fruits with mild overexpression exhibited reduced size as a result of reduced cell expansion, rather than impaired cell division. Additionally, SlMBP22 overexpression in tomato not only affected proanthocyanidin (PA) accumulation but also altered seed dormancy. Taken together, these findings may provide new insights into the knowledge of B_s MADS-box genes in flower and fruit development in tomato.

Mitogen-activated protein kinase 4 is obligatory for late pollen and early fruit development in tomato

Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules regulating vegetative and reproductive development of plants. However, the molecular mechanisms of the SlMPK4 gene in tomato pollen and fruit development remain elusive. SlMPK4 is preferentially and highly expressed in tomato stamens and its mRNA levels increase during early flower development, peaking at the mature pollen stage. Either up- or downregulation of SlMPK4 expression had no significant effect on tomato vegetative growth. However, RNAi-mediated suppression of SlMPK4 caused defects in pollen development, resulting in pollen abortion. The aborted pollen grains were either malformed or collapsed and completely lacked viability, resulting in a predominantly reduced fruit set rate in RNAi lines compared with control and overexpressing transgenic plants. Interestingly, seed development was inhibited in RNAi lines. Moreover, >12% of emasculated RNAi flowers developed seedless fruits without pollination. Anthers can produce typical microspore mother cells as well as uninucleate microspores, according to cytological investigations, while binucleate pollen ceased to produce typical mature pollen. Pollen abortion was further confirmed by transmission electron microscopy analysis at the binucleate stage in RNAi plants. The exine layer in aberrant pollen had a normal structure, while the intine layer appeared thicker. Suppression of SlMPK4 affects the transcript level of genes related to cell wall formation and modification, cell signal transduction, and metabolic and biosynthetic processes. A subset of genes that may be putative substrates of plant MAPKs were also differentially changed in RNAi transgenic flowers. Taken together, these results suggest that SlMPK4 plays a critical role in regulating pollen development and fruit development in tomato plants.

Interplays between auxin and GA signaling coordinate early fruit development

Phytohormones and their interactions are critical for fruit development and, are key topics in horticulture research. Auxin, together with gibberellic acid (GA), promotes cell division and expansion, thus subsequently regulates fruit development and enlargement after fertilization. Auxin and GA related mutants show parthenocarpy (fruit formation without fertilization of ovule) in many plant species, indicating that these hormones and possibly their interactions play a key role in the regulation of fruit initiation and development. Recent studies have shown clear molecular and genetic evidence that ARF/IAA and DELLA protein interact each other and regulate both auxin and GA signaling pathways in response to auxin and GA during fruit growth in horticultural plants, tomato (the most studied freshy fruit) and strawberry (the model of Rosaceae). These recent findings provide new insights into the mechanisms by which plant hormones auxin and GA regulate fruit development.

Abscisic Acid: Role in Fruit Development and Ripening

Abscisic acid (ABA) is a plant growth regulator known for its functions, especially in seed maturation, seed dormancy, adaptive responses to biotic and abiotic stresses, and leaf and bud abscission. ABA activity is governed by multiple regulatory pathways that control ABA biosynthesis, signal transduction, and transport. The transport of the ABA signaling molecule occurs from the shoot (site of synthesis) to the fruit (site of action), where ABA receptors decode information as fruit maturation begins and is significantly promoted. The maximum amount of ABA is exported by the phloem from developing fruits during seed formation and initiation of fruit expansion. In the later stages of fruit ripening, ABA export from the phloem decreases significantly, leading to an accumulation of ABA in ripening fruit. Fruit growth, ripening, and senescence are under the control of ABA, and the mechanisms governing these processes are still unfolding. During the fruit ripening phase, interactions between ABA and ethylene are found in both climacteric and non-climacteric fruits. It is clear that ABA regulates ethylene biosynthesis and signaling during fruit ripening, but the molecular mechanism controlling the interaction between ABA and ethylene has not yet been discovered. The effects of ABA and ethylene on fruit ripening are synergistic, and the interaction of ABA with other plant hormones is an essential determinant of fruit growth and ripening. Reaction and biosynthetic mechanisms, signal transduction, and recognition of ABA receptors in fruits need to be elucidated by a more thorough study to understand the role of ABA in fruit ripening. Genetic modifications of ABA signaling can be used in commercial applications to increase fruit yield and quality. This review discusses the mechanism of ABA biosynthesis, its translocation, and signaling pathways, as well as the recent findings on ABA function in fruit development and ripening.

Integrative Morphological, Physiological, Proteomics Analyses of Jujube Fruit Development Provide Insights Into Fruit Quality Domestication From Wild Jujube to Cultivated Jujube

Jujube (Ziziphus jujuba) was domesticated from wild jujube (Z. jujuba var. spinosa). Here, integrative physiological, metabolomic, and comparative proteomic analyses were performed to investigate the fruit expansion and fruit taste components in a jujube cultivar 'Junzao' and a wild jujube 'Qingjiansuanzao' with contrasting fruit size and taste. We revealed that the duration of cell division and expansion largely determined the final fruit size, while the intercellular space in the mesocarp dictated the ratio of mesocarp volume in mature fruits. The high levels of endogenous gibbereline3 (GA) and zeatin in the growing fruit of 'Junzao' were associated with their increased fruit expansion. Compared with 'Junzao,' wild jujube accumulated lower sugars and higher organic acids. Furthermore, several protein co-expression modules and important member proteins correlated with fruit expansion, sugar synthesis, and ascorbic acid metabolism were identified. Among them, GA20OX involved in GA biosynthesis was identified as a key protein regulating fruit expansion, whereas sucrose-6-phosphate synthase (SPS) and neutral invertase (NINV) were considered as key enzymes promoting sugar accumulation and as major factors regulating the ratio of sucrose to hexose in jujube fruits, respectively. Moreover, the increase of Nicotinamide adenine dinucleotide-Malate dehydrogenase (NAD-MDH) activity and protein abundance were associated with the malic acid accumulation, and the high accumulation of ascorbic acid in wild jujube was correlated with the elevated abundance of GalDH, ZjAPXs, and MDHAR1, which are involved in the ascorbic acid biosynthesis and recycling pathways. Overall, these results deepened the understanding of mechanisms regulating fruit expansion and sugar/acids metabolisms in jujube fruit.

Effects of Pollination Interventions, Plant Age and Source on Hormonal Patterns and Fruit Set of Date Palm (Phoenix dactylifera L.)

Date palm is widely propagated through conventional offshoots. It is also produced through a tissue culture technique due to the limited number of offshoots produced throughout the course of a palm’s life. Being dioecious, it is a cross-pollinated tree that can be naturally or artificially pollinated. Tissue-cultured plants often have abnormal epigenetic or genetic changes that affect specific phenotypic characteristics. The growth of parthenocarpic fruits in date palms is mostly induced by hormonal imbalances in certain tissues. The major hormones in parthenocarpic fruits are auxins (IAA), gibberellins (GA3), and abscisic acid (ABA). Parthenocarpic, or abnormal fruit development, is an undesirable trait for date palm growers since it drastically reduces farm income. The current study was therefore conducted over two seasons to confirm previous observations and included conventional offshoot-derived trees (CO) and tissue culture-derived ones (TC) of the cultivar Barhee. According to the observed ratio of the fruiting abnormalities, two date palm tree ages were selected, i.e., 6 and 13 years. Two pollination interventions were used: pollination of naturally open female spathes (NOP) and pollination of forced open female spathes (FOP). Plant hormones, IAA, GA3, and ABA were identified just before pollination and at specific intervals after pollination for up to 85 days. The ratio of the abnormal fruit set was identified 5 days after pollination. Significant differences were observed in hormonal levels between tree ages as well as between tree propagation sources. Young TC trees (6-year-old) had high abnormal fruit sets compared to CO date palm trees that were the same age. During the early fruit growth and development phases, CO date palms had much higher amounts of IAA and GA3 than TC date palms. However, ABA concentrations were surprisingly higher in the TC trees during the early fruit growth stages, while it immediately decreased after pollination in the CO date palms. The ratio of abnormal fruits was significantly reduced in the 13-year-old TC date palms, and no differences were observed compared to the CO ones. The levels of IAA, GA3, and ABA hormones in both young and old date palms derived through CO or TC followed similar patterns. The critical observations regarding the ABA pattern in the old TC date palms (13-year-old) gradually dropped after pollination, which was identical to the CO ones, whereas it was the opposite in the young 6-year-old TC date palm plants.

Auxin Metabolism Is Involved in Fruit Set and Early Fruit Development in the Parthenocarpic Tomato "R35-P"

Parthenocarpic tomato can set fruit and develop without pollination and exogenous hormone treatments under unfavorable environmental conditions, which is beneficial to tomato production from late fall to early spring in greenhouses. In this study, the endogenous hormones in the ovaries of the parthenocarpic tomato line "R35-P" (stigma removed or self-pollination) and the non-parthenocarpic tomato line "R35-N" (self-pollination) at four stages between preanthesis and postanthesis investigated, using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). A nearly twofold IAA (indoleacetic acid) content was found in "R35-P" rather than in "R35-N" at -2 and 0 days after anthesis (DAA). Except at -2 DAA, a lower ABA (abscisic acid) content was observed in Pe (stigma removed in "R35-P") compared to that in Ps (self-pollination in "R35-P") or CK (self-pollination in "R35-N"). After pollination, although the content of GA₁ (gibberellins acid 1) in CK increased, the levels of GAs (gibberellins acids) were notably low. At all four stages, a lower SA (salicylic acid) content was found in Ps and CK than in Pe, while the content and the change trend were similar in Ps and CK. The variation tendencies of JA (jasmonic acid) varied among Pe, Ps, and CK at the studied periods. Furthermore, KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses of transcriptomic data identified 175 differentially expressed genes (DEGs) related to plant hormone signal transduction, including 63 auxin-related genes, 27 abscisic acid-related genes, 22 ethylene-related genes, 16 cytokinin-related genes, 16 salicylic acid-related genes, 14 brassinosteroid-related genes, 13 jasmonic acid-related genes, and 4 gibberellin-related genes at -2 DAA and 0 DAA. Our results suggest that the fate of a fruit set or degeneration occurred before anthesis in tomato. Auxins, whose levels were independent of pollination and fertilization, play prominent roles in controlling a fruit set in "R35-P," and other hormones are integrated in a synergistic or antagonistic way.

Modification of Threonine-825 of SlBRI1 Enlarges Cell Size to Enhance Fruit Yield by Regulating the Cooperation of BR-GA Signaling in Tomato

Brassinosteroids (BRs) are growth-promoting phytohormones that can efficiently function by exogenous application at micromolar concentrations or by endogenous fine-tuning of BR-related gene expression, thus, precisely controlling BR signal strength is a key factor in exploring the agricultural potential of BRs. BRASSINOSTEROID INSENSITIVE1 (BRI1), a BR receptor, is the rate-limiting enzyme in BR signal transduction, and the phosphorylation of each phosphorylation site of SlBRI1 has a distinct effect on BR signal strength and botanic characteristics. We recently demonstrated that modifying the phosphorylation sites of tomato SlBRI1 could improve the agronomic traits of tomato to different extents; however, the associated agronomic potential of SlBRI1 phosphorylation sites in tomato has not been fully exploited. In this research, the biological functions of the phosphorylation site threonine-825 (Thr-825) of SlBRI1 in tomato were investigated. Phenotypic analysis showed that, compared with a tomato line harboring SlBRI1, transgenic tomato lines expressing SlBRI1 with a nonphosphorylated Thr-825 (T825A) exhibited a larger plant size due to a larger cell size and higher yield, including a greater plant height, thicker stems, longer internodal lengths, greater plant expansion, a heavier fruit weight, and larger fruits. Molecular analyses further indicated that the autophosphorylation level of SlBRI1, BR signaling, and gibberellic acid (GA) signaling were elevated when SlBRI1 was dephosphorylated at Thr-825. Taken together, the results demonstrated that dephosphorylation of Thr-825 can enhance the functions of SlBRI1 in BR signaling, which subsequently activates and cooperates with GA signaling to stimulate cell elongation and then leads to larger plants and higher yields per plant. These results also highlight the agricultural potential of SlBRI1 phosphorylation sites for breeding high-yielding tomato varieties through precise control of BR signaling.

Genome-wide identification of auxin response factor (ARF) family in kiwifruit (Actinidia chinensis) and analysis of their inducible involvements in abiotic stresses

Auxin response factor (ARF) acts as a vital component of auxin signaling and participates in growth, development, and stress responses in plants. In the present study, we comprehensively analyzed kiwifruit's (Actinidia chinensis) ARF genes (AcARFs) and their involvement in abiotic stress response. We identified a total of 41 AcARFs encoding ARFs in the A. chinensis genome. AcARF genes were characterized by the classic ARF_resp and a B3 domain and primarily localized on the cytoplasm and nucleus. AcARFs were categorized into eight subgroups as per the phylogenetic analysis. Synteny analysis showed that 35 gene pairs in AcARF family underwent segmental and whole genome duplication events. Promoter cis-element prediction revealed that AcARFs might be involved in abiotic factors related to stress response, which was later assessed and validated by qRT-PCR based expression analysis. Additionally, AcARFs showed tissue-specific expression. These findings extend our understanding of the functional roles of AcARFs in stress responses. Taken together, the systematic annotation of the AcARF family genes provides a platform for the functional and evolutionary study, which might help in elucidating the precise roles of the AcARFs in stress responses.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01011-4.

Overexpression of MtRAV3 enhances osmotic and salt tolerance and inhibits growth of Medicago truncatula

Related to ABI3/VP1 (RAV) transcription factors play important roles in regulating plant growth and stress tolerance, which have been studied in many plant species, but have remained largely unidentified in legumes. To functionally characterize RAV in legumes, MtRAV3 from legume model plant Medicago truncatula was isolated and its function was investigated by overexpressing MtRAV3 in M. truncatula. Expression analysis demonstrated that MtRAV3 was markedly induced by NaCl and polyethylene glycol (PEG). MtRAV3 overexpression enhanced tolerance of transgenic M. truncatula to mannitol, drought and salt stresses, and induced the expression of adversity-related genes, including MtWRKY76, MtMYB61, cold-acclimation specific protein 31 (MtCAS31), alternative oxidase 1 (MtAOX1) and ethylene response factor 1 (MtERF1). There were lower relative electrolyte leakage and higher chlorophyll content of leaves in the MtRAV3 overexpression plants than in wild type plants under both salt and drought stress. MtRAV3 overexpression M. truncatula were featured by some phenotypes of dwarfing, late flowering, more branches, smaller flower and leaf organs. Further investigations showed that the expression levels of DWARF14 (MtD14), CAROTENOID CLEAVAGE DIOXYGENASES 7 (MtCCD7) and GA3-oxidase1 (MtGA3ox1), which related to dwarf and branch phenotype, were obviously reduced, as well as MtGA3ox1' (MTR_1g011580), GA20-oxidase1 (MtGA20ox1), MtGA20ox1' (MTR_1g102070) and GA20-oxidase2 (MtGA20ox2) involved in gibberellins (GAs) pathway. Overall, our results revealed that MtRAV3 exerted an important role in adversity response and plant growth, was a multifunctional gene in M. truncatula, which provided reference for genetic improvement of alfalfa (Medicago sativa).

Knockout of Auxin Response Factor SlARF4 Improves Tomato Resistance to Water Deficit

Auxin response factors (ARFs) play important roles in various plant physiological processes; however, knowledge of the exact role of ARFs in plant responses to water deficit is limited. In this study, SlARF4, a member of the ARF family, was functionally characterized under water deficit. Real-time fluorescence quantitative polymerase chain reaction (PCR) and β-glucuronidase (GUS) staining showed that water deficit and abscisic acid (ABA) treatment reduced the expression of SlARF4. SlARF4 was expressed in the vascular bundles and guard cells of tomato stomata. Loss of function of SlARF4 (arf4) by using Clustered Regularly Interspaced Short Palindromic Repeats/Cas 9 (CRISPR/Cas 9) technology enhanced plant resistance to water stress and rehydration ability. The arf4 mutant plants exhibited curly leaves and a thick stem. Malondialdehyde content was significantly lower in arf4 mutants than in wildtype plants under water stress; furthermore, arf4 mutants showed higher content of antioxidant substances, superoxide dismutase, actual photochemical efficiency of photosystem II (PSII), and catalase activities. Stomatal and vascular bundle morphology was changed in arf4 mutants. We identified 628 differentially expressed genes specifically expressed under water deficit in arf4 mutants; six of these genes, including ABA signaling pathway-related genes, were differentially expressed between the wildtype and arf4 mutants under water deficit and unlimited water supply. Auxin responsive element (AuxRE) elements were found in these genes' promoters indicating that SlARF4 participates in ABA signaling pathways by regulating the expression of SlABI5/ABF and SCL3, thereby influencing stomatal morphology and vascular bundle development and ultimately improving plant resistance to water deficit.

SlTPL1 Silencing Induces Facultative Parthenocarpy in Tomato

Facultative parthenocarpy is of great practical value. However, the molecular mechanism underlying facultative parthenocarpy remains elusive. Transcriptional co-repressors (TPL) act as a central regulatory hub controlling all nine phytohormone pathways. Previously, we proved that SlTPLs participate in the auxin signaling pathway by interacting with auxin/indole acetic acid (Aux/IAAs) in tomato; however, their function in fruit development has not been studied. In addition to their high expression levels during flower development, the interaction between SlTPL1 and SlIAA9 stimulated the investigation of its functional significance via RNA interference (RNAi) technology, whereby the translation of a protein is prevented by selective degradation of its encoded mRNA. Down-regulation of SlTPL1 resulted in facultative parthenocarpy. Plants of SlTPL1-RNAi transgenic lines produced similar fruits which did not show any pleiotropic effects under normal conditions. However, they produced seedless fruits upon emasculation and under heat stress conditions. Furthermore, SlTPL1-RNAi flower buds contained higher levels of cytokinins and lower levels of abscisic acid. To reveal how SlTPL1 regulates facultative parthenocarpy, RNA-seq was performed to identify genes regulated by SlTPL1 in ovaries before and after fruit set. The results showed that down-regulation of SlTPL1 resulted in reduced expression levels of cytokinin metabolism-related genes, and all transcription factors such as MYB, CDF, and ERFs. Conversely, down-regulation of SlTPL1 induced the expression of genes related to cell wall and cytoskeleton organization. These data provide novel insights into the molecular mechanism of facultative tomato parthenocarpy and identify SlTPL1 as a key factor regulating these processes.

How Hormones and MADS-Box Transcription Factors Are Involved in Controlling Fruit Set and Parthenocarpy in Tomato

Fruit set is the earliest phase of fruit growth and represents the onset of ovary growth after successful fertilization. In parthenocarpy, fruit formation is less affected by environmental factors because it occurs in the absence of pollination and fertilization, making parthenocarpy a highly desired agronomic trait. Elucidating the genetic program controlling parthenocarpy, and more generally fruit set, may have important implications in agriculture, considering the need for crops to be adaptable to climate changes. Several phytohormones play an important role in the transition from flower to fruit. Further complexity emerges from functional analysis of floral homeotic genes. Some homeotic MADS-box genes are implicated in fruit growth and development, displaying an expression pattern commonly observed for ovary growth repressors. Here, we provide an overview of recent discoveries on the molecular regulatory gene network underlying fruit set in tomato, the model organism for fleshy fruit development due to the many genetic and genomic resources available. We describe how the genetic modification of components of this network can cause parthenocarpy, discussing the contribution of hormonal signals and MADS-box transcription factors.

Productivity and quality of horticultural crops through co-inoculation of arbuscular mycorrhizal fungi and plant growth promoting bacteria

Associations between plants and microorganisms exist in nature, and they can either be beneficial or detrimental to host plants. Promoting beneficial plant-microbe interaction for increased crop yield and quality is one pathway to eco-friendly and sustainable crop production. Arbuscular mycorrhizal fungi (AMF) and plant growth promoting bacteria (PGPB) are microorganisms that are beneficial to horticultural crops. Arbuscular mycorrhizal fungi establish symbioses with plant roots which help to improve nutrient uptake by the host plant and alter its physiology to withstand external abiotic factors and pathogens. Plant growth promoting bacteria promote plant growth either directly by aiding resource acquisition and controlling the levels of plant hormones or indirectly by reducing the inhibitory effects of phytopathogens. Co-inoculation of both organisms combines the benefits of each for increased crop productivity. Even though the co-inoculation of PGPB and AMF have been shown to enhance the yield and quality of crops, its benefits have fully not been exploited for horticultural crops. In this review, the response of horticultural crops to co-inoculation with PGPB and AMF with particular interest to the impact on the yield and crop quality was discussed. We explained some of the mechanisms responsible for the synergy between AMF and PGPB in plant growth promotion. Finally, suggestions on areas that need to be researched further to exploit and improve the effects of these organisms were highlighted.

Identification and Expression Analysis of Hormone Biosynthetic and Metabolism Genes in the 2OGD Family for Identifying Genes That May Be Involved in Tomato Fruit Ripening

Phytohormones play important roles in modulating tomato fruit development and ripening. The 2-oxoglutarate-dependent dioxygenase (2OGD) superfamily containing several subfamilies involved in hormone biosynthesis and metabolism. In this study, we aimed to identify hormone biosynthesis and metabolism-related to 2OGD proteins in tomato and explored their roles in fruit development and ripening. We identified nine 2OGD protein subfamilies involved in hormone biosynthesis and metabolism, including the gibberellin (GA) biosynthetic protein families GA20ox and GA3ox, GA degradation protein families C19-GA2ox and C20-GA2ox, ethylene biosynthetic protein family ACO, auxin degradation protein family DAO, jasmonate hydroxylation protein family JOX, salicylic acid degradation protein family DMR6, and strigolactone biosynthetic protein family LBO. These genes were differentially expressed in different tomato organs. The GA degradation gene SlGA2ox2, and the auxin degradation gene SlDAO1, showed significantly increased expression from the mature-green to the breaker stage during tomato fruit ripening, accompanied by decreased endogenous GA and auxin, indicating that SlGA2ox2 and SlDAO1 were responsible for the reduced GA and auxin concentrations. Additionally, exogenous gibberellin 3 (GA₃) and indole-3-acetic acid (IAA) treatment of mature-green fruits delayed fruit ripening and increased the expression of SlGA2ox2 and SlDAO1, respectively. Therefore, SlGA2ox2 and SlDAO1 are implicated in the degradation of GAs and auxin during tomato fruit ripening.

Auxin and ethylene regulation of fruit set

With the forecasted fast increase in world population and global climate change, providing sufficient amounts of quality food becomes a major challenge for human society. Seed and fruit crop yield is determined by developmental processes including flower initiation, pollen fertility and fruit set. Fruit set is defined as the transition from flower to young fruit, a key step in the development of sexually reproducing higher plants. Plant hormones have important roles during flower pollination and fertilization, leading to fruit set. Moreover, it is well established that fruit set can be triggered by phytohormones like auxin and gibberellins (GAs), in the absence of fertilization, both hormones being commonly used to produce parthenocarpic fruits and to increase fruit yield. Additionally, a number of studies highlighted the role of ethylene in plant reproductive organ development. The present review integrates current knowledge on the roles of auxin and ethylene in different steps of the fruit set process with a specific emphasis on the interactions between the two hormones. A deeper understanding of the interplay between auxin and ethylene may provide new leads towards designing strategies for a better control of fruit initiation and ultimately yield.

Phytohormone and Transcriptomic Analysis Reveals Endogenous Cytokinins Affect Kiwifruit Growth under Restricted Carbon Supply

Following cell division, fruit growth is characterized by both expansion through increases in cell volume and biomass accumulation in cells. Fruit growth is limited by carbon starvation; however, the mechanism controlling fruit growth under restricted carbohydrate supply is poorly understood. In a previous study using red-fleshed kiwifruit, we showed that long-term carbon starvation had detrimental effects on carbohydrate, anthocyanin metabolism, and fruit growth. To elucidate the mechanisms underlying the reduction in fruit growth during kiwifruit development, we integrated phytohormone profiling with transcriptomic and developmental datasets for fruit under high or low carbohydrate supplies. Phytohormone profiling of the outer pericarp tissue of kiwifruit showed a 6-fold reduction in total cytokinin concentrations in carbon-starved fruit, whilst other hormones were less affected. Principal component analysis visualised that cytokinin composition was distinct between fruit at 16 weeks after mid bloom, based on their carbohydrate supply status. Cytokinin biosynthetic genes (IPT, CYP735A) were significantly downregulated under carbon starvation, in agreement with the metabolite data. Several genes that code for expansins, proteins involved in cell wall loosening, were also downregulated under carbon starvation. In contrast to other fleshy fruits, our results suggest that cytokinins not only promote cell division, but also drive fruit cell expansion and growth in kiwifruit.

Atemoya fruit development and cytological aspects of GA3-induced growth and parthenocarpy

The exogenous application of GA₃ to atemoya tree flowers induces parthenocarpy, and in association with artificial pollination, it increases the fruit size. Morphological, anatomical, ultrastructural, and chemical aspects were evaluated during development of (1) fruit produced by artificial pollination (AP), (2) fruit from AP followed by the application of 250 ppm GA₃, and (3) parthenocarpic fruit induced by the application of 1000 ppm GA₃. Fruit growth showed a sigmoidal pattern, with development occurring in three phases: (I) cell division, (II) cell differentiation, and (III) maturation. Phase I presented cells with large nuclear volumes and a large population of organelles, phase II presented cells with a reduction in cytoplasm and an increase in vacuole volume, and phase III presented cells with an increase in plastids with reserve compounds. The application of GA₃, in association with pollination, precedes cytological events and delays when applied exclusively. GA₃ promotes the growth of pollinated fruits by stimulating cell division and expansion, which occur in association with reduced seed production, and the GA₃ induces parthenocarpy by maintaining division and stimulating cell expansion. The absence of seeds accounts for the smaller size of the parthenocarpic fruits, and the lower accumulation of calcium accounts for less firm fruit.

Identification and characterization of cherry (Cerasus pseudocerasus G. Don) genes responding to parthenocarpy induced by GA3 through transcriptome analysis

Background

Fruit set after successful pollination is key for the production of sweet cherries, and a low fruit-setting rate is the main problem in production of this crop. As gibberellin treatment can directly induce parthenogenesis and satisfy the hormone requirement during fruit growth and development, such treatment is an important strategy for improving the fruit-setting rate of sweet cherries. Previous studies have mainly focused on physiological aspects, such as fruit quality, fruit size, and anatomical structure, whereas the molecular mechanism remains clear.

Results

In this study, we analyzed the transcriptome of ‘Meizao’ sweet cherry fruit treated with gibberellin during the anthesis and hard-core periods to identify genes associated with parthenocarpic fruit set. A total of 25,341 genes were identified at the anthesis and hard-core stages, 765 (681 upregulated, 84 downregulated) and 186 (141 upregulated, 45 downregulated) of which were significant differentially expressed genes (DEGs) at the anthesis and the hard-core stages after gibberellin 3 (GA3) treatment, respectively. Based on DEGs between the control and GA3 treatments, the GA3 response mainly involves parthenocarpic fruit set and cell division. Exogenous gibberellin stimulated sweet cherry fruit parthenocarpy and enlargement, as verified by qRT-PCR results of related genes as well as the parthenocarpic fruit set and fruit size. Based on our research and previous studies in Arabidopsis thaliana, we identified key genes associated with parthenocarpic fruit set and cell division. Interestingly, we observed patterns among sweet cherry fruit setting-related DEGs, especially those associated with hormone balance, cytoskeleton formation and cell wall modification.

Conclusions

Overall, the result provides a possible molecular mechanism regulating parthenocarpic fruit set that will be important for basic research and industrial development of sweet cherries.

Electronic supplementary material

The online version of this article (10.1186/s12863-019-0746-8) contains supplementary material, which is available to authorized users.

Recent Advances in Hormonal Regulation and Cross-Talk during Non-Climacteric Fruit Development and Ripening

Fleshy fruits are characterized by having a developmentally and genetically controlled, highly intricate ripening process, leading to dramatic modifications in fruit size, texture, color, flavor, and aroma. Climacteric fruits such as tomato, pear, banana, and melon show a ripening-associated increase in respiration and ethylene production and these processes are well-documented. In contrast, the hormonal mechanism of fruit development and ripening in non-climacteric fruit, such as strawberry, grape, raspberry, and citrus, is not well characterized. However, recent studies have shown that non-climacteric fruit development and ripening, involves the coordinated action of different hormones, such as abscisic acid (ABA), auxin, gibberellins, ethylene, and others. In this review, we discuss and evaluate the recent research findings concerning the hormonal regulation of non-climacteric fruit development and ripening and their cross-talk by taking grape, strawberry, and raspberry as reference fruit species.

Fruit ripening: the role of hormones, cell wall modifications, and their relationship with pathogens

Fruits result from complex biological processes that begin soon after fertilization. Among these processes are cell division and expansion, accumulation of secondary metabolites, and an increase in carbohydrate biosynthesis. Later fruit ripening is accomplished by chlorophyll degradation and cell wall lysis. Fruit maturation is an essential step to optimize seed dispersal, and is controlled by a complex network of transcription factors and genetic regulators that are strongly influenced by phytohormones. Abscisic acid (ABA) and ethylene are the major regulators of ripening and senescence in both dry and fleshy fruits, as demonstrated by numerous ripening-defective mutants, effects of exogenous hormone application, and transcriptome analyses. While ethylene is the best characterized player in the final step of a fruit's life, ABA also has a key regulatory role, promoting ethylene production and acting as a stress-related hormone in response to drought and pathogen attack. In this review, we focus on the role of ABA and ethylene in relation to the interconnected biotic and abiotic phenomena that affect ripening and senescence. We integrate and discuss the most recent data available regarding these biological processes, which are crucial for post-harvest fruit conservation and for food safety.

Gibberellins modulate auxin responses during tomato (Solanum lycopersicum L.) fruit development

In tomato, auxin and gibberellins (GAs) interact with each other to drive fruit growth and development. While the role of auxin in directing GA biosynthesis and signal is already known, very little information has been obtained about GA-mediated control of auxin signalling and response. Interestingly, we show that gibberellic acid (GA₃ ) is able to modify the expression of several auxin signalling genes in the partial auxin-insensitive diageotropica (dgt) mutant, suggesting that GAs may override the control of DGT on auxin signal. Procera (pro) mutation, which confers a constitutively active GA signal, enhances the effects of exogenous auxin, indicating that PRO may act as a negative effector of auxin responses in fruits. Indeed, transcript modulation of some auxin/indole acetic acid and auxin response factor genes in auxin-treated dgt/pro fruits suggests that PRO controls their expression possibly bypassing DGT. It was also shown that GA biosynthesis, in response to auxin treatment, is largely controlled by DGT. It is therefore conceivable that the DGT-mediated increase of active GAs in auxin-treated or pollinated fruits would promote PRO degradation, which in turn activates part of the auxin signalling cascade.

Insight into the B3Transcription Factor Superfamily and Expression Profiling of B3 Genes in Axillary Buds after Topping in Tobacco(Nicotiana tabacum L.)

Members of the plant-specific B3 transcription factor superfamily play important roles in various growth and developmental processes in plants. Even though there are many valuable studies on B3 genes in other species, little is known about the B3 superfamily in tobacco. We identified 114 B3 proteins from tobacco using comparative genome analysis. These proteins were classified into four subfamilies based on their phylogenetic relationships, and include the ARF, RAV, LAV, and REM subfamilies. The chromosomal locations, gene structures, conserved protein motifs, and sub-cellular localizations of the tobacco B3 proteins were analyzed. The patterns of exon-intron numbers and arrangement and the protein structures of the tobacco B3 proteins were in general agreement with their phylogenetic relationships. The expression patterns of 114 B3 genes revealed that many B3 genes show tissue-specific expression. The expression levels of B3 genes in axillary buds after topping showed that the REM genes are mainly up-regulated in response to topping, while the ARF genes are down-regulated after topping.

Genome-wide identification and expression analysis of brassinosteroid action-related genes during the shoot growth of moso bamboo

Brassinosteroids (BRs) are a group of plant steroid hormones that play crucial roles in a range of plant growth and development processes. BR action includes active BR formation by a complex biosynthesis process and driving BR biological function through signal transduction. Although the characterization of several BR action-related genes has been conducted in a few model plants, systematic information about these genes in bamboo is still lacking. We identified 64 genes related to BR action from the genome of moso bamboo (Phyllostachys edulis), including twenty that participated in BR biosynthesis and forty-four involved in BR signal transduction. The characteristics of all these candidate genes were identified by bioinformatics methods, including the gene structures, basic physical and chemical properties of proteins, conserved domains and evolutionary relationships. Based on the transcriptome data, the candidate genes demonstrated different expression patterns, which were further validated by qRT-PCR using templates from bamboo shoots with different heights. Thirty-four positive and three negative co-expression modules were identified by 44 candidate genes in the newly emerging bamboo shoot. The gene expression patterns and co-expression modules of BR action-related genes in bamboo shoots indicated that they might function to promote bamboo growth through BR biosynthesis and signal transduction processes. This study provides the first step towards the cloning and functional dissection of the role of BR action-related genes in moso bamboo, which also presents an excellent opportunity for genetic engineering using the candidate genes to improve bamboo quantity and quality.

An AGAMOUS MADS-box protein, SlMBP3, regulates the speed of placenta liquefaction and controls seed formation in tomato

AGAMOUS (AG) MADS-box transcription factors have been shown to play crucial roles in floral organ and fruit development in angiosperms. Here, we isolated a tomato (Solanum lycopersicum) AG MADS-box gene SlMBP3 and found that it is preferentially expressed in flowers and during early fruit developmental stages in the wild-type (WT), and in the Nr (never ripe) and rin (ripening inhibitor) mutants. Its transcripts are notably accumulated in the pistils; transcripts abundance decrease during seed and placental development, increasing again during flower development. SlMBP3-RNAi tomato plants displayed fleshy placenta without locular gel and extremely malformed seeds with no seed coat, while SlMBP3-overexpressing plants exhibited advanced liquefaction of the placenta and larger seeds. Enzymatic activities related to cell wall modification, and the contents of cell wall components and pigments were dramatically altered in the placentas of SlMBP3-RNAi compared with the WT. Alterations in these physiological features were also observed in the placentas of SlMBP3-overexpressing plants. The lignin content of mature seeds in SlMBP3-RNAi lines was markedly lower than that in the WT. RNA-seq and qRT-PCR analyses revealed that genes involved in seed development and the biosynthesis of enzymes related to cell wall modification, namely gibberellin, indole-3-acetic acid, and abscisic acid were down-regulated in the SlMBP3-RNAi lines. Taking together, our results demonstrate that SlMBP3 is involved in the regulation of placenta and seed development in tomato.

Aberrant Stamen Development is Associated with Parthenocarpic Fruit Set Through Up-Regulation of Gibberellin Biosynthesis in Tomato

Parthenocarpy, a process in which fruit set occurs without fertilization, leads to the production of seedless fruit. A number of floral homeotic mutants with abnormal stamen development exhibit parthenocarpic fruit set. Flower development is thought to repress ovary growth before anthesis. However, the mechanism of parthenocarpic fruit development caused by aberrant flower formation is poorly understood. To investigate the molecular mechanism of parthenocarpic fruit development in floral homeotic mutants, we performed functional analysis of Tomato APETALA3 (TAP3) by loss-of-function approaches. Organ-specific promoter was used to induce organ-specific loss of function in stamen and ovary/fruit. We observed increased cell expansion in tap3 mutants and TAP3-RNAi lines during parthenocarpic fruit growth. These were predominantly accompanied by the up-regulation of GA biosynthesis genes, including SlGA20ox1, SlGA20ox2, and SlGA20ox3, as well as reduced expression of the GA-inactivating gene SlGA2ox1 and the auxin signaling gene SlARF7 involved in a crosstalk between GA and auxin. These transcriptional profiles are in agreement with the GA levels in these lines. These results suggest that stamen development negatively regulates fruit set by repressing the GA biosynthesis.

Evolution and Diversification of FRUITFULL Genes in Solanaceae

Ecologically and economically important fleshy edible fruits have evolved from dry fruit numerous times during angiosperm diversification. However, the molecular mechanisms that underlie these shifts are unknown. In the Solanaceae there has been a major shift to fleshy fruits in the subfamily Solanoideae. Evidence suggests that an ortholog of FRUITFULL (FUL), a transcription factor that regulates cell proliferation and limits the dehiscence zone in the silique of Arabidopsis, plays a similar role in dry-fruited Solanaceae. However, studies have shown that FUL orthologs have taken on new functions in fleshy fruit development, including regulating elements of tomato ripening such as pigment accumulation. FUL belongs to the core eudicot euFUL clade of the angiosperm AP1/FUL gene lineage. The euFUL genes fall into two paralogous clades, euFULI and euFULII. While most core eudicots have one gene in each clade, Solanaceae have two: FUL1 and FUL2 in the former, and MBP10 and MBP20 in the latter. We characterized the evolution of the euFUL genes to identify changes that might be correlated with the origin of fleshy fruit in Solanaceae. Our analyses revealed that the Solanaceae FUL1 and FUL2 clades probably originated through an early whole genome multiplication event. By contrast, the data suggest that the MBP10 and MBP20 clades are the result of a later tandem duplication event. MBP10 is expressed at weak to moderate levels, and its atypical short first intron lacks putative transcription factor binding sites, indicating possible pseudogenization. Consistent with this, our analyses show that MBP10 is evolving at a faster rate compared to MBP20. Our analyses found that Solanaceae euFUL gene duplications, evolutionary rates, and changes in protein residues and expression patterns are not correlated with the shift in fruit type. This suggests deeper analyses are needed to identify the mechanism underlying the change in FUL ortholog function.

Female reproductive organ formation: A multitasking endeavor

Multicellular organisms, such as plants, fungi, and animals, develop organs with specialized functions. Major challenges in developing such structures include establishment of polarity along three axes (apical-basal, medio-lateral, and dorso-ventral/abaxial-adaxial), specification of tissue types and their coordinated growth, and maintenance of communication between the organ and the entire organism. The gynoecium of the model plant Arabidopsis thaliana embodies the female reproductive organ and has proven an excellent model system for studying organ establishment and development, given its division into different regions with distinct symmetries and highly diverse tissue types. Upon pollination, the gynoecium undergoes dramatic changes in morphology and developmental programming to form the seed-containing fruit. In this review, we wish to provide a detailed overview of the molecular and genetic mechanisms that are known to guide gynoecium and fruit development in A. thaliana. We describe networks of key genetic regulators and their interactions with hormonal dynamics in driving these developmental processes. The discoveries made to date clearly demonstrate that conclusions drawn from studying gynoecium and fruit development in flowering plants can be used to further our general understanding of organ formation across the plant kingdom. Importantly, this acquired knowledge is increasingly being used to improve fruit and seed crops, facilitated by the recent profound advances in genomics, cloning, and gene-editing technologies.

The Interaction between DELLA and ARF/IAA Mediates Crosstalk between Gibberellin and Auxin Signaling to Control Fruit Initiation in Tomato

Fruit initiation following fertilization in angiosperms is strictly regulated by phytohormones. In tomato (Solanum lycopersicum), auxin and gibberellin (GA) play central roles in promoting fruit initiation. Without fertilization, elevated GA or auxin signaling can induce parthenocarpy (seedless fruit production). The GA-signaling repressor SlDELLA and auxin-signaling components SlIAA9 and SlARF7 repress parthenocarpy, but the underlying mechanism is unknown. Here, we show that SlDELLA and the SlARF7/SlIAA9 complex mediate crosstalk between GA and auxin pathways to regulate fruit initiation. Yeast-two-hybrid and coimmunoprecipitation assays showed that SlARF7 and additional activator SlARFs interact with SlDELLA and SlIAA9 through distinct domains. SlARF7/SlIAA9 and SlDELLA antagonistically modulate the expression of feedback-regulated genes involved in GA and auxin metabolism, whereas SlARF7/SlIAA9 and SlDELLA coregulate the expression of fruit growth-related genes. Analysis of procera (della), SlARF7 RNAi (with downregulated expression of multiple activator SlARFs), and entire (iaa9) single and double mutants indicated that these genes additively affect parthenocarpy, supporting the notion that the SlARFs/SlIAA9 and SlDELLA interaction plays an important role in regulating fruit initiation. Analysis of the GA-deficient mutant gib1 showed that active GA biosynthesis and signaling are required for auxin-induced fruit initiation. Our study reveals how direct crosstalk between auxin- and GA-signaling components is critical for tomato fruit initiation.

Tomato AUXIN RESPONSE FACTOR 5 regulates fruit set and development via the mediation of auxin and gibberellin signaling

Auxin response factors (ARFs) encode transcriptional factors that function in the regulation of plant development processes. A tomato ARF gene, SlARF5, was observed to be expressed at high levels in emasculated ovaries but maintained low expression levels in pollinated ovaries. The amiRNA SlARF5 lines exhibited ovary growth and formed seedless fruits following emasculation. These parthenocarpic fruits developed fewer locular tissues, and the fruit size and weight were decreased in transgenic lines compared to those of wild-type fruits. Gene expression analysis demonstrated that several genes involved in the auxin-signaling pathway were downregulated, whereas some genes involved in the gibberellin-signaling pathway were enhanced by the decreased SlARF5 mRNA levels in transgenic plants, indicating that SlARF5 may play an important role in regulating both the auxin- and gibberellin-signaling pathways during fruit set and development.

Characterization of Conserved and Novel microRNAs in Lilium lancifolium Thunb. by High-Throughput Sequencing

MicroRNAs (miRNAs) are among the class of noncoding small RNA molecules and play a crucial role in post-transcriptional regulation in plants. Although Lilium is one of the most popular ornamental flowers worldwide, however, there is no report on miRNAs identification. In the present study, therefore, miRNAs and their targets were identified from flower, leaf, bulblet and bulb of Lilium lancifolium Thunb. by high-throughput sequencing and bioinformatics analysis. In this study, a total of 38 conserved miRNAs belonging to 17 miRNA families and 44 novel miRNAs were identified. In total, 366 target genes for conserved miRNAs and 415 target genes for novel miRNAs were predicted. The majority of the target genes for conserved miRNAs were transcriptional factors and novel miRNAs targeted mainly protein coding genes. A total of 53 cleavage sites belonging to 6 conserved miRNAs families and 14 novel miRNAs were identified using degradome sequencing. Twenty-three miRNAs were randomly selected, then, their credibility was confirmed using northern blot or stem-loop qRT-PCR. The results from qRT-PCR analysis showed the expression pattern of 4 LL-miRNAs was opposite to their targets. Therefore, our finding provides an important basis to understand the biological functions of miRNAs in Lilium.

Functional Dissection of Auxin Response Factors in Regulating Tomato Leaf Shape Development

The phytohormone auxin is involved in many aspects of plant growth and developmental processes. The tomato Aux/IAA transcription factor SlIAA9/ENTIRE/E plays an important role in leaf morphogenesis and fruit development, and the E gene encodes a protein from the Aux/IAA family of auxin response repressors. Both SlIAA9-RNAi transgenic and entire (e) mutant plants reduce the leaf complexity in tomato, but the underlying mechanism is not yet completely resolved. Auxin signaling is known to regulate target genes expression via Aux/IAA and ARFs (auxin response factors) transcriptional regulators. ARFs mediate a wide range of developmental processes. Through an Y2H (yeast two-hybrid) assay coupled with expression profiling of the SlARF genes family, we identified a group of ARFs: SlARF6A, SlARF8A, SlARF8B, and SlARF24. Pull-down and BiFC (Bimolecular Fluorescence Complementation) results demonstrated that these SlARFs interact with SlIAA9 in vitro and in vivo, and the e mutation altered the expression patterns of multiple SlARFs. The simple leaves of the e mutant were partially converted to wild-type compound leaves by VIGS (virus-induced gene silencing) of these four SlARFs. Furthermore, IAA content in these samples was significantly increased compared to the e mutant. In addition, SlARF6A and SlARF24 bound to the SlPIN1 promoter and act as transcriptional activators to regulate genes expression involved in leaflet initiation. It may also suggest that SlARFs regulate leaf morphology through direct binding to auxin-responsive genes in the absence of SlIAA9, providing an insight for the role of SlARFs in leaf shape development.

The association of hormone signalling genes, transcription and changes in shoot anatomy during moso bamboo growth

Moso bamboo is a large, woody bamboo with the highest ecological, economic and cultural value of all the bamboo types and accounts for up to 70% of the total area of bamboo grown. However, the spatiotemporal variation role of moso bamboo shoot during growth period is still unclear. We found that the bamboo shoot growth can be divided into three distinct periods, including winter growth, early growth and late growth based on gene expression and anatomy. In the early growth period, lateral buds germinated from the top of the bamboo joint in the shoot tip. Intercalary meristems grew vigorously during the winter growth period and early growth period, but in the late growth period, mitosis in the intercalary meristems decreased. The expression of cell cycle-associated genes and the quantity of differentially expressed genes were higher in early growth than those in late growth, appearing to be influenced by hormonal concentrations. Gene expression analysis indicates that hormone signalling genes play key roles in shoot growth, while auxin signalling genes play a central role. In situ hybridization analyses illustrate how auxin signalling genes regulate apical dominance, meristem maintenance and lateral bud development. Our study provides a vivid picture of the dynamic changes in anatomy and gene expression during shoot growth in moso bamboo, and how hormone signalling-associated genes participate in moso bamboo shoot growth.

Phytochromobilin deficiency impairs sugar metabolism through the regulation of cytokinin and auxin signaling in tomato fruits

Phytochomes and plant hormones have been emerging as important regulators of fleshy fruit biology and quality traits; however, the relevance of phytochrome-hormonal signaling crosstalk in controlling fruit development and metabolism remains elusive. Here, we show that the deficiency in phytochrome chromophore phytochromobilin (PΦB) biosynthesis inhibits sugar accumulation in tomato (Solanum lycopersicum) fruits by transcriptionally downregulating sink- and starch biosynthesis-related enzymes, such as cell-wall invertases, sucrose transporters and ADP-glucose pyrophosphorylases. PΦB deficiency was also shown to repress fruit chloroplast biogenesis, which implicates more limited production of photoassimilates via fruit photosynthesis. Genetic and physiological data revealed the involvement of auxins and cytokinins in mediating the negative impact of PΦB deficiency on fruit sink strength and chloroplast formation. PΦB deficiency was shown to transcriptionally repress type-A TOMATO RESPONSE REGULATORs and AUXIN RESPONSE FACTORs both in pericarp and columella, suggesting active phytochrome-hormonal signaling crosstalk in these tissues. Data also revealed that PΦB deficiency influences fruit ripening by delaying the climacteric rise in ethylene production and signaling. Altogether, the data uncover the impact of phytochromobilin deficiency in fine-tuning sugar metabolism, chloroplast formation and the timing of fruit ripening and also reveal a link between auxins, cytokinins and phytochromes in regulating sugar import and accumulation in fruits.

Metabolomics for Plant Improvement: Status and Prospects

Post-genomics era has witnessed the development of cutting-edge technologies that have offered cost-efficient and high-throughput ways for molecular characterization of the function of a cell or organism. Large-scale metabolite profiling assays have allowed researchers to access the global data sets of metabolites and the corresponding metabolic pathways in an unprecedented way. Recent efforts in metabolomics have been directed to improve the quality along with a major focus on yield related traits. Importantly, an integration of metabolomics with other approaches such as quantitative genetics, transcriptomics and genetic modification has established its immense relevance to plant improvement. An effective combination of these modern approaches guides researchers to pinpoint the functional gene(s) and the characterization of massive metabolites, in order to prioritize the candidate genes for downstream analyses and ultimately, offering trait specific markers to improve commercially important traits. This in turn will improve the ability of a plant breeder by allowing him to make more informed decisions. Given this, the present review captures the significant leads gained in the past decade in the field of plant metabolomics accompanied by a brief discussion on the current contribution and the future scope of metabolomics to accelerate plant improvement.

Comprehensive transcriptomics and proteomics analyses of pollinated and parthenocarpic litchi (Litchi chinensis Sonn.) fruits during early development

Litchi (Litchi chinensis Sonn.) is an important fruit that is widely cultivated in tropical and subtropical areas. In this study, we used RNA-Seq and iTRAQ technologies to compare the transcriptomes and proteomes of pollinated (polLFs) and parthenocarpic (parLFs) litchi fruits during early development (1 day, 2 days, 4 days and 6 days). We identified 4,864 DEGs in polLFs and 3,672 in parLFs, of which 2,835 were shared and 1,051 were specifically identified in parLFs. Compared to po1LFs, 768 DEGs were identified in parLFs. iTRAQ analysis identified 551 DEPs in polLFs and 1,021 in parLFs, of which 305 were shared and 526 were exclusively identified in parLFs. We found 1,127 DEPs in parLFs compared to polLFs at different stages. Further analysis revealed some DEGs/DEPs associated with abscisic acid, auxin, ethylene, gibberellin, heat shock protein (HSP), histone, ribosomal protein, transcription factor and zinc finger protein (ZFP). WGCNA identified a large set of co-expressed genes/proteins in polLFs and parLFs. In addition, a cross-comparison of transcriptomic and proteomic data identified 357 consistent DEGs/DEPs in polLFs and parLFs. This is the first time that protein/gene changes have been studied in polLFs and parLFs, and the findings improve our understanding of litchi parthenocarpy.

Identification and Expression Profiling of the Auxin Response Factors in Dendrobium officinale under Abiotic Stresses

Auxin response factor (ARF) proteins play roles in plant responses to diverse environmental stresses by binding specifically to the auxin response element in the promoters of target genes. Using our latest public Dendrobium transcriptomes, a comprehensive characterization and analysis of 14 DnARF genes were performed. Three selected DnARFs, including DnARF1, DnARF4, and DnARF6, were confirmed to be nuclear proteins according to their transient expression in epidermal cells of Nicotiana benthamiana leaves. Furthermore, the transcription activation abilities of DnARF1, DnARF4, and DnARF6 were tested in a yeast system. Our data showed that DnARF6 is a transcriptional activator in Dendrobium officinale. To uncover the basic information of DnARF gene responses to abiotic stresses, we analyzed their expression patterns under various hormones and abiotic treatments. Based on our data, several hormones and significant stress responsive DnARF genes have been identified. Since auxin and ARF genes have been identified in many plant species, our data is imperative to reveal the function of ARF mediated auxin signaling in the adaptation to the challenging Dendrobium environment.

De novo Transcriptome Profiling of Flowers, Flower Pedicels and Pods of Lupinus luteus (Yellow Lupine) Reveals Complex Expression Changes during Organ Abscission

Yellow lupine (Lupinus luteus L., Taper c.), a member of the legume family (Fabaceae L.), has an enormous practical importance. Its excessive flower and pod abscission represents an economic drawback, as proper flower and seed formation and development is crucial for the plant's productivity. Generative organ detachment takes place at the basis of the pedicels, within a specialized group of cells collectively known as the abscission zone (AZ). During plant growth these cells become competent to respond to specific signals that trigger separation and lead to the abolition of cell wall adhesion. Little is known about the molecular network controlling the yellow lupine organ abscission. The aim of our study was to establish the divergences and similarities in transcriptional networks in the pods, flowers and flower pedicels abscised or maintained on the plant, and to identify genes playing key roles in generative organ abscission in yellow lupine. Based on de novo transcriptome assembly, we identified 166,473 unigenes representing 219,514 assembled unique transcripts from flowers, flower pedicels and pods undergoing abscission and from control organs. Comparison of the cDNA libraries from dropped and control organs helped in identifying 1,343, 2,933 and 1,491 differentially expressed genes (DEGs) in the flowers, flower pedicels and pods, respectively. In DEG analyses, we focused on genes involved in phytohormonal regulation, cell wall functioning and metabolic pathways. Our results indicate that auxin, ethylene and gibberellins are some of the main factors engaged in generative organ abscission. Identified 28 DEGs common for all library comparisons are involved in cell wall functioning, protein metabolism, water homeostasis and stress response. Interestingly, among the common DEGs we also found an miR169 precursor, which is the first evidence of micro RNA engaged in abscission. A KEGG pathway enrichment analysis revealed that the identified DEGs were predominantly involved in carbohydrate and amino acid metabolism, but some other pathways were also targeted. This study represents the first comprehensive transcriptome-based characterization of organ abscission in L. luteus and provides a valuable data source not only for understanding the abscission signaling pathway in yellow lupine, but also for further research aimed at improving crop yields.

The parthenocarpic hydra mutant reveals a new function for a SPOROCYTELESS-like gene in the control of fruit set in tomato

Fruit set is an essential process to ensure successful sexual plant reproduction. The development of the flower into a fruit is actively repressed in the absence of pollination. However, some cultivars from a few species are able to develop seedless fruits overcoming the standard restriction of unpollinated ovaries to growth. We report here the identification of the tomato hydra mutant that produces seedless (parthenocarpic) fruits. Seedless fruit production in hydra plants is linked to the absence of both male and female sporocyte development. The HYDRA gene is therefore essential for the initiation of sporogenesis in tomato. Using positional cloning, virus-induced gene silencing and expression analysis experiments, we identified the HYDRA gene and demonstrated that it encodes the tomato orthologue of SPOROCYTELESS/NOZZLE (SPL/NZZ) of Arabidopsis. We found that the precocious growth of the ovary is associated with changes in the expression of genes involved in gibberellin (GA) metabolism. Our results support the conservation of the function of SPL-like genes in the control of sporogenesis in plants. Moreover, this study uncovers a new function for the tomato SlSPL/HYDRA gene in the control of fruit initiation.

The Solanum lycopersicum auxin response factor SlARF2 participates in regulating lateral root formation and flower organ senescence

ARF2 as apleiotropic developmental regulator has been reported in Arabidopsis thaliana and tomato (Solanum lycopersicum). The present study showed SlARF2 transcripts in all tomato plant tissues but with higher accumulation in flowers. During bud-anthesis stages, SlARF2 transcripts showed a dynamic expression pattern in sepal, stamen, ovary and petal. Hormone treatment analysis suggested that SlARF2 transcript accumulation was positively regulated by auxin and gibberellic acid, and negatively regulated by ethylene in tomato seedlings. Phenotypes and molecular analyses of SlARF2-upregulated transgenic tomato indicated that SlARF2 regulated tomato lateral root formation and flower organ senescence may be partially mediated by regulating the gene expression of auxin and ethylene response factors. The data enlarges the functional characterization of SlARF2 in tomato, and broadens our understanding of auxin signaling in regulating plant growth and development.

SlTIR1 is involved in crosstalk of phytohormones, regulates auxin-induced root growth and stimulates stenospermocarpic fruit formation in tomato

TIR1 and its homologs act as auxin receptors and play important roles in plant growth and development in Arabidopsis thaliana. An auxin receptor homolog Solanum lycopersicum TIR1 (SlTIR1) has been isolated from tomato cultivar Micro-Tom, and SlTIR1 over-expression results in parthenocarpic fruit formation. In this study, the promoter driving the β-glucuronidase (GUS) expression vector was constructed and stably transformed into Micro-Tom seedlings. The SlTIR1 promoter driving GUS expression accumulated predominantly in the leaf and vasculature in transgenic seedlings. Promoter analysis identified an auxin-response element (AuxRE) and two gibberellic acid (GA)-response elements in the SlTIR1 promoter. Quantitative PCR showed that SlTIR1 transcript level was down-regulated by naphthaleneacetic acid, ethephon and abscisic acid and up-regulated by GA. Furthermore, because of the lack of ability to form reproductive seeds in SlTIR1 over-expressing Micro-Tom, this limits further exploration of potential roles of SlTIR1 in auxin signaling. Here, an antisense vector and an over-expression vector of the SlTIR1 gene were stably transformed into Micro-Tom and Ailsa Craig tomato, respectively. Phenotypes and physiological analyses indicated that SlTIR1 regulated primary root growth and auxin-associated lateral root formation in Micro-Tom. Meanwhile, SlTIR1 also stimulated abnormal seed development, so-called stenospermocarpy, in Ailsa Craig. Transcript accumulations of auxin-signaling genes determined by quantitative PCR were consistent with the idea that SlTIR1 regulated plant growth and development, partially mediated by controlling the mRNA levels of auxin-signaling genes. Our work demonstrates that SlTIR1 regulated auxin-induced root growth and stimulated stenospermocarpic fruit formation. SlTIR1 may be a key mediator of the crosstalk among auxin and other hormones to co-regulate plant growth and development.