The fruit, the whole fruit, and everything about the fruit

Potential of reproductive traits in functional ecology: A quantitative comparison of variability in floral, fruit, and leaf traits

Despite their claimed low intraspecific variability, plant reproductive traits are less frequently used in functional ecology. Here we focused on underrepresented plant organs, i.e. flowers and fruits, by comparing their traits with well-established leaf traits. We evaluated 16 functional traits (six floral, six fruit, and four leaf traits) in a randomly selected group of woody species under comparable environmental conditions. We aimed to assess interspecific and intraspecimen variability and explore the potential of the proposed flower and fruit traits for ecological research. Traits related to the dry mass of flowers and fruits exhibited the highest interspecific variability, while carbon content traits in flowers and leaves had the lowest. At a specimen level, specific leaf area revealed the highest variation. Carbon content traits for all organs demonstrated the least intraspecimen variability, with flower carbon content being the least variable. Our study revealed connections between the newly proposed traits and widely recognized functional traits, uncovering intriguing links between the established traits and the floral and fruit traits upon which we focused. This complements the already well-recognized variability in plant form and function with additional insights into reproductive processes.

Worldwide productivity and research trend on fruit quality: a bibliometric study

Introduction

As one of the important sources of food for human beings, fruits have been extensively studied. To better guide basic and applied research, it is urgent to conduct a systematic analysis of these studies based on extensive literature collection.

Methods

Based on the Web of Science Core Collection database, this study uses R language and CiteSpace to conduct bibliometric analysis and data mining on the literatures related to fruit quality from January 2013 to June 2023.

Results

The results indicated that among various fruits, tomatoes have been most frequently studied with special interests in photosynthesis, fruit development, and molecular breeding. The research direction primarily focused on fruit resistance and storage characteristics. Among the indicators related to fruit quality, antioxidant activity has the highest co-occurrence with other indicators of fruit quality, especially with nutrients such as anthocyanins, phenolic substances, sugars, and fruit firmness.

Discussion

Currently, adaptation to stress and antioxidant activity are recognized as prominent research focal points in this field. Fruit morphology, particularly fruit size, irrigation methods, application of molecular technology, and infection prevention, represent potential areas of interests in future research on fruit quality.

Embryo-Endosperm Interactions

In angiosperms, double fertilization triggers the concomitant development of two closely juxtaposed tissues, the embryo and the endosperm. Successful seed development and germination require constant interactions between these tissues, which occur across their common interface. The embryo-endosperm interface is a complex and poorly understood compound apoplast comprising components derived from both tissues, across which nutrients transit to fuel embryo development. Interface properties, which affect molecular diffusion and thus communication, are themselves dynamically regulated by molecular and physical dialogues between the embryo and endosperm. We review the current understanding of embryo-endosperm interactions, with a focus on the structure, properties, and function of their shared interface. Concentrating on Arabidopsis, but with reference to other species, we aim to situate recent findings within the broader context of seed physiology, developmental biology, and genetic factors such as parental conflicts over resource allocation.

Programmed Cell Death in Developing Brachypodium distachyon Grain

The normal developmental sequence in a grass grain entails the death of several maternal and filial tissues in a genetically regulated process termed programmed cell death (PCD). The progression and molecular aspects of PCD in developing grains have been reported for domesticated species such as barley, rice, maize and wheat. Here, we report a detailed investigation of PCD in the developing grain of the wild model species Brachypodium distachyon. We detected PCD in developing Brachypodium grains using molecular and histological approaches. We also identified in Brachypodium the orthologs of protease genes known to contribute to grain PCD and surveyed their expression. We found that, similar to cereals, PCD in the Brachypodium nucellus occurs in a centrifugal pattern following anthesis. However, compared to cereals, the rate of post-mortem clearance in the Brachypodium nucellus is slower. However, compared to wheat and barley, mesocarp PCD in Brachypodium proceeds more rapidly in lateral cells. Remarkably, Brachypodium mesocarp PCD is not coordinated with endosperm development. Phylogenetic analysis suggests that barley and wheat possess more vacuolar processing enzymes that drive nucellar PCD compared to Brachypodium and rice. Our expression analysis highlighted putative grain-specific PCD proteases in Brachypodium. Combined with existing knowledge on grain PCD, our study suggests that the rate of nucellar PCD moderates grain size and that the pattern of mesocarp PCD influences grain shape.

CcBLH6, a bell-like homeodomain-containing transcription factor, regulates the fruit lignification pattern

CcBLH6 is a bell-like homeodomain-containing transcription factor that plays an important role of lignin biosynthesis in the control of fruit lignification pattern in Camellia chekiangoleosa. The fruit of Camellia chekiangoleosa has a unique lignification pattern that features with a thick pericarp containing a low level of lignification. Yet the fruit lignification pattern and the regulatory network of responsible gene transcription are poorly understood. Here, we characterized a bell-like homeodomain-containing (BLH) transcription factor from C. chekiangoleosa, CcBLH6, in the control of fruit lignification. CcBLH6 expression was highly correlated with the unique lignification pattern during fruit development. The ectopic expression of CcBLH6 promoted the lignification process of stem and root in Arabidopsis. We found that expression of genes related to lignin biosynthesis and its transcriptional regulation was altered in transgenic lines. In a Camellia callus-transformation system, overexpression of CcBLH6 greatly enhanced the expression of genes related to lignin biosynthesis and its transcriptional regulation was altered in transgenic lines. In the callus-transformation system, overexpression of CcBLH6 greatly enhanced the lignification of parenchymal cells, and the regulation of several genes involved in lignin accumulation was largely consistent between Arabidopsis and Camellia. Our study reveals a positive role of CcBLH6 in the regulation of lignin biosynthesis during fruit lignification in Camellia.

A MADS-box gene, EgMADS21, negatively regulates EgDGAT2 expression and decreases polyunsaturated fatty acid accumulation in oil palm (Elaeis guineensis Jacq.)

EgMADS21 regulates PUFA accumulation in oil palm. Oil palm (Elaeis guineensis Jacq.) is the most productive world oil crop, accounting for 36% of world plant oil production. However, the molecular mechanism of the transcriptional regulation of fatty acid accumulation and lipid synthesis in the mesocarp of oil palm by up- or downregulating the expression of genes involved in related pathways remains largely unknown. Here, an oil palm MADS-box gene, EgMADS21, was screened in a yeast one-hybrid assay using the EgDGAT2 promoter sequence as bait. EgMADS21 is preferentially expressed in early mesocarp developmental stages in oil palm fruit and presents a negative correlation with EgDGAT2 expression. The direct binding of EgMADS21 to the EgDGAT2 promoter was confirmed by electrophoretic mobility shift assay. Subsequently, transient expression of EgMADS21 in oil palm protoplasts revealed that EgMADS21 not only binds to the EgDGAT2 promoter but also negatively regulates the expression of EgDGAT2. Furthermore, EgMADS21 was stably overexpressed in transgenic oil palm embryoids by Agrobacterium-mediated transformation. In three independent transgenic lines, EgDGAT2 expression was significantly suppressed by the expression of EgMADS21. The content of linoleic acid (C18:2) in the three transgenic embryoids was significantly decreased, while that of oleic acid (C18:1) was significantly increased. Combined with the substrate preference of EgDGAT2 identified in previous research, the results demonstrate the molecular mechanism by which EgMADS21 regulates EgDGAT2 expression and ultimately affects fatty acid accumulation in the mesocarp of oil palm.

The Impact of Fruit Etiolation on Quality of Seeds in Tobacco

Seed's maturity and integrity are essential requirements for germination, and they rely on nutrients availability and a correct phytohormones' balance. These aspects are prerequisites for prompt germination at the end of the dormancy period and strictly depend on chloroplast metabolism and photosynthesis. In the present work, capsules of Nicotiana tabacum were grown in dark during the whole post-anthesis period. Among others, photosynthetic rates, dormancy, and phytohormones levels in seeds were found to be significantly different with respect to controls. In particular, etiolated capsules had expectedly reduced photosynthetic rates and, when compared to controls, their seeds had an increased mass and volume, an alteration in hormones level, and a consequently reduced dormancy. The present findings show how, during fruit development, the presence of light and the related fruit's photosynthetic activity play an indirect but essential role for reaching seeds maturity and dormancy. Results highlight how unripe fruits are versatile organs that, depending on the environmental conditions, may facultatively behave as sink or source/sink with associated variation in seed's reserves and phytohormone levels.

Nitric oxide in the physiology and quality of fleshy fruits

Fruits are unique to flowering plants and confer a selective advantage as they facilitate seed maturation and dispersal. In fleshy fruits, development and ripening are associated with numerous structural, biochemical, and physiological changes, including modifications in the general appearance, texture, flavor, and aroma, which ultimately convert the immature fruit into a considerably more attractive and palatable structure for seed dispersal by animals. Treatment with exogenous nitric oxide (NO) delays fruit ripening, prevents chilling damage, promotes disease resistance, and enhances the nutritional value. The ripening process is influenced by NO, which operates antagonistically to ethylene, but it also interacts with other regulatory molecules such as abscisic acid, auxin, jasmonic acid, salicylic acid, melatonin, and hydrogen sulfide. NO content progressively declines during fruit ripening, with concomitant increases in protein nitration and nitrosation, two post-translational modifications that are promoted by reactive nitrogen species. Dissecting the intimate interactions of NO with other ripening-associated factors, including reactive oxygen species, antioxidants, and the aforementioned phytohormones, remains a challenging subject of research. In this context, integrative 'omics' and gene-editing approaches may provide additional knowledge of the impact of NO in the regulatory processes involved in controlling physiology and quality traits in both climacteric and non-climacteric fruits.

CjPLE, a PLENA-like gene, is a potential regulator of fruit development via activating the FRUITFUL homolog in Camellia

Fruit patterning involves the cooperation of multiple processes, including metabolic change, cell differentiation, and cell expansion. The FRUITFUL (FUL) and SHATTERPROOF1/2 (SHPs) MADS-box genes are master regulators directing fruit patterning in several eudicots. However, the regulatory mechanisms of the FUL-SHP network in different fruit types remain unclear. Here, we characterized the functions of an ortholog (CjPLE) of SHPs from Camellia japonica. We showed that CjPLE was predominantly expressed in stamen and carpel tissues during the early stage of floral development and that transcripts were abundant in the pericarp tissues during fruit development. The ectopic expression of CjPLE in Arabidopsis caused enhanced development of the carpels, whereas no defects in floral identity were observed. To investigate the downstream targets of CjPLE, overexpression transformants were analysed through a callus transformation system in Camellia azalea. We examined the expression levels of potential downstream target genes and found that two previously identified APETALA1-like genes (CjAPL1/2) were significantly up-regulated. We showed that CjPLE directly bound to the CArG motifs in the promoter region of CjAPL1 (the FUL ortholog). Taken together, our results reveal a possible positive regulation of FUL by SHP in the control of fruit development in Camellia.

Functional traits but not environmental gradients explain seed weight in Mongolian plant species

Seed weight varies by several orders of magnitude among vascular plant species. However, the importance of potential drivers such as environmental conditions and plant functional traits have rarely been assessed for a larger taxonomic sample. We collected seeds of 148 species from 237 sites spread across Mongolia and compared their weight among the major zonal vegetation types, taxonomic groups and a set of functional traits (growth form, dispersal mode, fruit type, storage organs and palatability). Seed weight strongly varied among all functional traits and taxonomic groups, but no differences among vegetation zones were detected. These results suggest a low impact of environmental conditions on the evolution of seed weight, contrasting the strong phylogenetic signal.

Nitric oxide on/off in fruit ripening

Fruit ripening is a complex physiological process involving significant external and internal modifications. Classic edible fleshy fruits have been classified as climacteric or non-climacteric according to their dependence on the phyto hormone ethylene; however, data have increasingly confirmed the involvement of the free radical nitric oxide (NO) in this process. Moreover, the exogenous application of NO demonstrates its beneficial effects on fruit quality.

Abscisic acid and sucrose regulate tomato and strawberry fruit ripening through the abscisic acid-stress-ripening transcription factor

Although great progress has been made towards understanding the role of abscisic acid (ABA) and sucrose in fruit ripening, the mechanisms underlying the ABA and sucrose signalling pathways remain elusive. In this study, transcription factor ABA-stress-ripening (ASR), which is involved in the transduction of ABA and sucrose signalling pathways, was isolated and analysed in the nonclimacteric fruit, strawberry and the climacteric fruit, tomato. We have identified four ASR isoforms in tomato and one in strawberry. All ASR sequences contained the ABA stress- and ripening-induced proteins and water-deficit stress-induced proteins (ABA/WDS) domain and all ASR transcripts showed increased expression during fruit development. The expression of the ASR gene was influenced not only by sucrose and ABA, but also by jasmonic acid (JA) and indole-3-acetic acid (IAA), and these four factors were correlated with each other during fruit development. ASR bound the hexose transporter (HT) promoter, which contained a sugar box that activated downstream gene expression. Overexpression of the ASR gene promoted fruit softening and ripening, whereas RNA interference delayed fruit ripening, as well as affected fruit physiological changes. Change in ASR gene expression influenced the expression of several ripening-related genes such as CHS, CHI, F3H, DFR, ANS, UFGT, PG, PL, EXP1/2, XET16, Cel1/2 and PME. Taken together, this study may provide new evidence on the important role of ASR in cross-signalling between ABA and sucrose to regulate tomato and strawberry fruit ripening. The findings of this study also provide new insights into the regulatory mechanism underlying fruit development.

Evolution of fruit development genes in flowering plants

The genetic mechanisms regulating dry fruit development and opercular dehiscence have been identified in Arabidopsis thaliana. In the bicarpellate silique, valve elongation and differentiation is controlled by FRUITFULL (FUL) that antagonizes SHATTERPROOF1-2 (SHP1/SHP2) and INDEHISCENT (IND) at the dehiscence zone where they control normal lignification. SHP1/2 are also repressed by REPLUMLESS (RPL), responsible for replum formation. Similarly, FUL indirectly controls two other factors ALCATRAZ (ALC) and SPATULA (SPT) that function in the proper formation of the separation layer. FUL and SHP1/2 belong to the MADS-box family, IND and ALC belong to the bHLH family and RPL belongs to the homeodomain family, all of which are large transcription factor families. These families have undergone numerous duplications and losses in plants, likely accompanied by functional changes. Functional analyses of homologous genes suggest that this network is fairly conserved in Brassicaceae and less conserved in other core eudicots. Only the MADS box genes have been functionally characterized in basal eudicots and suggest partial conservation of the functions recorded for Brassicaceae. Here we do a comprehensive search of SHP, IND, ALC, SPT, and RPL homologs across core-eudicots, basal eudicots, monocots and basal angiosperms. Based on gene-tree analyses we hypothesize what parts of the network for fruit development in Brassicaceae, in particular regarding direct and indirect targets of FUL, might be conserved across angiosperms.