Characterization of a bZIP gene highly expressed during ripening of the peach fruit

Genome-wide identification and molecular characterization of the MAPK family members in sand pear (Pyrus pyrifolia)

BACKGROUND

'Whangkeumbae', a highly regarded variety of sand pear, is celebrated in the market for its distinctive and superior flavor. However, the rapid production of ethylene after harvest significantly shortens its shelf life, becoming a major limiting factor for enhancing its commercial value. Mitogen-activated protein kinases (MAPKs) are a highly conserved family of transferases in eukaryotes. Although the importance of this family has been extensively studied in other plants, the precise composition and functional mechanisms of MAPK members in sand pear remain elusive. A genome-wide identification and molecular characterization of the MAPK gene family were conducted in Pyrus pyrifolia. This comprehensive analysis aimed to elucidate the genomic distribution, evolutionary relationships, and potential biological roles of MAPK genes in fruit senescence.

RESULTS

Four PpMAPKs were identified from our transcriptome data of sand pear, and 22 PpMAPK proteins were identified from the sand pear genome. Specifically, the transcriptomic PpMAPK3-L (GenBank accession number: PP992971), PpMAPK7-L (GenBank accession number: PP992972), PpMAPK10-L (GenBank accession number: PP992973), and PpMAPK16-L (GenBank accession number: PP992974) exhibited sequence homology values of 99.19%, 100%, 94.51%, and 95.75%, respectively, with their corresponding genomic counterparts (EVM0007944.1, EVM0004426.1, EVM0023771.1, EVM0027166.1). These findings indicate that the integrated analysis of transcriptomic and genomic data provides critical genetic insights into the MAPK genes in sand pear, culminating in the identification of a total of 25 PpMAPK genes in this species. Further phylogenetic analysis classified these genes into four subfamilies (A, B, C, and D), with subfamilies A and B each comprising six members, subfamily C with four members, and subfamily D with nine members. The potential functional differences among the gene members of each subfamily provide valuable clues for future research into MAPK signaling pathways. Further analysis by qRT-PCR revealed that the expression of four PpMAPK genes was positively correlated with fruit senescence in Pyrus pyrifolia. Additionally, interaction analysis revealed a significant interaction between PpMAPK3-L and PpbZIP2, which coordinatively regulate the senescence traits of fruits in sand pear through their joint influence during the senescence process.

CONCLUSION

The results of this study suggest that PpMAPK3-L, PpMAPK7-L, PpMAPK10-L, and PpMAPK16-L are likely to play pivotal roles in the maturation and senescence of sand pear fruit. Specifically, the interaction between PpMAPK3-L and PpbZIP2 could play a key role in the regulation of fruit senescence, indicating that the MAPK signaling pathway may modulate the fruit's physiological state through interactions with transcription factors. This finding offers significant insights for further investigation into the functions of MAPK genes in the maturation and senescence of sand pear fruit and provides a new direction for investigating biotechnological approaches for delaying senescence and prolonging shelf life.

Comprehensive Genome-Wide Investigation and Transcriptional Regulation of the bZIP Gene Family in Litchi Fruit Development

Litchi chinensis, a crucial tropical and subtropical fruit tree in southern China, is widely appreciated for its distinctive flavor, high nutritional value, and significant economic impact. The bZIP (basic leucine zipper) gene family plays an essential role in regulating key biological functions during plant growth and development. In this study, we performed a comprehensive bioinformatics analysis of the bZIP gene family in litchi to systematically elucidate its molecular characteristics and functional properties. A total of 55 bZIP gene family members were identified, with the encoded proteins containing between 129 and 845 amino acid residues and theoretical isoelectric points (pI) ranging from 4.85 to 10.23. Protein-protein interaction network analysis revealed that 46 proteins exhibited interaction relationships. Phylogenetic analysis classified these genes into 13 distinct subgroups (A-K, M, and S). Chromosomal localization analysis indicated that bZIP gene family members were successfully mapped to 15 chromosomes. Intraspecific collinearity analysis identified 39 segmental duplication events, while interspecific and single-gene collinearity analyses suggested evolutionary conservation, with only a few genes exhibiting duplication or loss events. Cis-acting element analysis revealed a total of 213 elements associated with growth and development, which may play an important role in fruit development regulation. The results of differential gene expression, related to fruit development across different litchi cultivars, tissues, and flowering stages, combined with qRT-PCR validation, suggest that LITCHI017015.m1 and LITCHI004463.m1 may be involved in the early regulation of fruit development, while LITCHI018843.m1 may play a regulatory role during the later stages of fruit development. These findings provide a strong theoretical foundation for understanding the roles of bZIP genes in litchi fruit growth and development, and lay the groundwork for further functional studies. This study has potential application value in litchi fruit development and genetic improvement.

Monitoring Apricot (Prunus armeniaca L.) Ripening Progression through Candidate Gene Expression Analysis

This study aimed at the monitoring of the apricot (Prunus armeniaca L.) ripening progression through the expression analysis of 25 genes related to fruit quality traits in nine cultivars with great differences in fruit color and ripening date. The level of pigment compounds, such as anthocyanins and carotenoids, is a key factor in food taste, and is responsible for the reddish blush color or orange skin and flesh color in apricot fruit, which are desirable quality traits in apricot breeding programs. The construction of multiple linear regression models to predict anthocyanins and carotenoids content from gene expression allows us to evaluate which genes have the strongest influence over fruit color, as these candidate genes are key during biosynthetic pathways or gene expression regulation, and are responsible for the final fruit phenotype. We propose the gene CHS as the main predictor for anthocyanins content, CCD4 and ZDS for carotenoids content, and LOX2 and MADS-box for the beginning and end of the ripening process in apricot fruit. All these genes could be applied as RNA markers to monitoring the ripening stage and estimate the anthocyanins and carotenoids content in apricot fruit during the ripening process.

The CmbZIP1 transcription factor of chrysanthemum negatively regulates shoot branching

The basic region/leucine zipper (bZIP) transcription factors play key roles in regulating diverse biological processes in plants. However, their participation in shoot branching has been rarely reported. Here, we isolated a CmbZIP1 transcription factor gene, a member of the bZIP family, from chrysanthemum. Subcellular localization analysis indicated that CmbZIP1 is a nuclear protein. Tissue-specific expression analysis indicated that CmbZIP1 was principally expressed in apical bud and axillary bud. Expression patterns analysis results showed that CmbZIP1 expression was suppressed in axillary buds in response to decapitation but increased in response to shade. Overexpression of CmbZIP1 in Arabidopsis inhibits its shoot branching. In addition, expression of auxin efflux protein PIN-FORMED 1 (PIN1) and auxin signaling components AUXIN RESISTANT 1/3 (AXR1, AXR3) were significantly up-regulated in overexpressing plants in comparison with wild type plants. Moreover, the transcript expression of BRANCHED 2 (AtBRC2) was also significantly up-regulated in overexpressing plants compared with the wild type. Altogether, these results suggest important and negative roles of CmbZIP1 in shoot branching. Our study extends the understanding of the function of bZIP transcription factors in plants and provides valuable gene resources for improving the architectural traits of ornamental plants.

SlAREB1 transcriptional activation of NOR is involved in abscisic acid-modulated ethylene biosynthesis during tomato fruit ripening

Many studies have shown that abscisic acid (ABA) regulates climacteric fruits ripening by inducing ethylene production. Nevertheless, the key components involved in the crosstalk between these two phytohormones in controlling fruit ripening remain unknown. SlAREB1, a downstream transcription factor in ABA signaling pathway, has been reported to mediate ABA signaling that regulates tomato ripening through induction of ethylene biosynthetic genes. NOR, a member of NAC domain family, was proved to act upstream of ethylene and essential for ripening- and ethylene-associated genes expression. Here, we found that the expression of SlAREB1 and NOR are both ABA-inducible, and SlAREB1 transcription reaches the peak level prior to NOR during the ripening process. Yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA) and dual luciferase assay indicated NOR as a novel direct target of SlAREB1. Transient over-expression of SlAREB1 in tomato fruits results in elevated expression of NOR as well as a number of downstream ethylene biosynthetic genes including SlACS2, SlACS4 and SlACO1, suggesting that SlAREB1 can mediate ABA signal to activate NOR transcription and ultimately promote ethylene synthesis. Based on these data, we present a model suggesting that the SlAREB1-NOR regulation is a crucial node modulating ABA-regulated ethylene biosynthesis during tomato fruit ripening.

A genetic genomics-expression approach reveals components of the molecular mechanisms beyond the cell wall that underlie peach fruit woolliness due to cold storage

Peach fruits subjected to prolonged cold storage (CS) to delay decay and over-ripening often develop a form of chilling injury (CI) called mealiness/woolliness (WLT), a flesh textural disorder characterized by lack of juiciness. Transcript profiles were analyzed after different lengths of CS and subsequent shelf life ripening (SLR) in pools of fruits from siblings of the Pop-DG population with contrasting sensitivity to develop WLT. This was followed by quantitative PCR on pools and individual lines of the Pop-DG population to validate and extend the microarray results. Relative tolerance to WLT development during SLR was related to the fruit's ability to recover from cold and the reactivation of normal ripening, processes that are probably regulated by transcription factors involved in stress protection, stress recovery and induction of ripening. Furthermore, our results showed that altered ripening in WLT fruits during shelf life is probably due, in part, to cold-induced desynchronization of the ripening program involving ethylene and auxin hormonal regulation of metabolism and cell wall. In addition, we found strong correlation between expression of RNA translation and protein assembly genes and the visual injury symptoms.

Prunus transcription factors: breeding perspectives

Many plant processes depend on differential gene expression, which is generally controlled by complex proteins called transcription factors (TFs). In peach, 1533 TFs have been identified, accounting for about 5.5% of the 27,852 protein-coding genes. These TFs are the reference for the rest of the Prunus species. TF studies in Prunus have been performed on the gene expression analysis of different agronomic traits, including control of the flowering process, fruit quality, and biotic and abiotic stress resistance. These studies, using quantitative RT-PCR, have mainly been performed in peach, and to a lesser extent in other species, including almond, apricot, black cherry, Fuji cherry, Japanese apricot, plum, and sour and sweet cherry. Other tools have also been used in TF studies, including cDNA-AFLP, LC-ESI-MS, RNA, and DNA blotting or mapping. More recently, new tools assayed include microarray and high-throughput DNA sequencing (DNA-Seq) and RNA sequencing (RNA-Seq). New functional genomics opportunities include genome resequencing and the well-known synteny among Prunus genomes and transcriptomes. These new functional studies should be applied in breeding programs in the development of molecular markers. With the genome sequences available, some strategies that have been used in model systems (such as SNP genotyping assays and genotyping-by-sequencing) may be applicable in the functional analysis of Prunus TFs as well. In addition, the knowledge of the gene functions and position in the peach reference genome of the TFs represents an additional advantage. These facts could greatly facilitate the isolation of genes via QTL (quantitative trait loci) map-based cloning in the different Prunus species, following the association of these TFs with the identified QTLs using the peach reference genome.

The role of abscisic acid in fruit ripening and responses to abiotic stress

The phytohormone abscisic acid (ABA) plays a crucial role not only in fruit development and ripening, but also in adaptive responses to biotic and abiotic stresses. In these processes, the actions of ABA are under the control of complex regulatory mechanisms involving ABA metabolism, signal transduction, and transport. The endogenous ABA content is determined by the dynamic balance between biosynthesis and catabolism, processes which are regulated by 9-cis-epoxycarotenoid dioxygenase (NCED) and ABA 8'-hydroxylase (CYP707A), respectively. ABA conjugation by cytosolic UDP-glucosyltransferases, or release by β-glucosidases, is also important for maintaining ABA homeostasis. Recently, multiple putative ABA receptors localized at different subcellular sites have been reported. Among these is a major breakthrough in the field of ABA signalling-the identification of a signalling cascade involving the PYR/PYL/RCAR protein family, the type 2C protein phosphatases (PP2Cs), and subfamily 2 of the SNF1-related kinases (SnRK2s). With regard to transport, two ATP-binding cassette (ABC) proteins and two ABA transporters in the nitrate transporter 1/peptide transporter (NRT1/PTR) family have been identified. In this review, we summarize recent research progress on the role of ABA in fruit ripening, stress response, and transcriptional regulation, and also the functional verification of both ABA-responsive and ripening-related genes. In addition, we suggest possible commercial applications of genetic manipulation of ABA signalling to improve fruit quality and yields.