Songling Bai

Dormancy-associated MADS-box genes and microRNAs jointly control dormancy transition in pear (Pyrus pyrifolia white pear group) flower bud

Highlight Short-term chilling in autumn activates the accumulation of CBF, which directly promotes DAM expression. DAMs subsequently inhibit FT2 expression to induce endo-dormancy; miR6390 might degrade DAM genes to release endo-dormancy.

Transcriptome analysis of bagging-treated red Chinese sand pear peels reveals light-responsive pathway functions in anthocyanin accumulation

Bagging is an efficient method to improve fruit colour development. This work reported a transcriptome analysis using bagging-treated red Chinese sand pear peels. In total, 8,870 differentially expressed genes were further analysed by a weighted gene co-expression network analysis and early-, middle- and late light-responsive genes were identified. An annotation analysis revealed several pathways involved in the different responsive stages. The presence of LONG HYPOCOTLY 5, CRY-DASH and a CONSTANS-like transcription factors among the early light-responsive genes indicated the pivotal role of light, especially blue light, in the biological changes that occurred after bag removal. Other light-responsive transcription factors were also identified from the three light-responsive stages. In addition, the light-responsive pattern of anthocyanin biosynthetic genes differed among the biosynthetic steps. Although yeast-one hybrid assay showed that most of the structural genes were regulated by PpMYB10, their different temporal expressive pattern suggested that besides PpMYB10, other light-responsive transcriptional factors were also involved in the regulation of anthocyanin biosynthesis. In summary, our transcriptome analysis provides knowledge of the transcriptional regulatory network operating during light responses, which results in anthocyanin accumulation and other significant physiological changes in red Chinese sand pear peels after bag removal.

Genome-wide identification, characterization, and expression analysis of the dehydrin gene family in Asian pear (Pyrus pyrifolia)

Dehydrins (DHNs) are a complex family of plant proteins that play an important role in protection of higher plant cells from dehydration and desiccation damage during environmental stresses, such as drought, high salinity, and low temperature. However, information on DHN genes of Asian pear (Pyrus pyrifolia), an economically important fruit crop grown in temperate regions in East Asia, e.g., China and Japan, is limited. To gain insights into this gene family in pear and to elucidate their roles in floral buds under low-temperature conditions, we performed a genome-wide identification, characterization, and expression analysis of DHN genes. Seven PpDHN genes were identified. Sequence alignment analysis of all putative proteins from these genes showed that all of the proteins contained a typical K-domain. These genes were categorized into SKn, YnSKn, YKn, and Kn groups based on gene characterization and phylogenetic relationships. Hierarchical cluster analyses showed that in non-stressed pear, PpDHN genes were expressed in all vegetative tissues except young leaves and shoot tips, in which PpDHN1, PpDHN2, and PpDHN4 were not expressed. Transcript levels of four PpDHN genes increased significantly in floral buds in response to low-temperature treatment, which indicated that they play important roles during stress adaptation. This study provides evidence that the family of pear DHN genes may function in tissue development and stress responses. The data will be valuable for further studies of the functions of DHN genes under different stress conditions in pear.

Characterization of 10 MADS-box genes from Pyrus pyrifolia and their differential expression during fruit development and ripening.

We cloned 10 Japanese pear (Pyrus pyrifolia) MIKC-type II MADS-box genes, and analyzed their expression during fruit development and ripening. PpMADS2-1 was APETALA (AP)1-like; PpMADS3-1 was FRUITFULL (FUL)/SQUAMOSA (SQUA)-like; PpMADS4-1 was AGAMOUS-like (AGL)6; PpMADS5-1 and PpMADS8-1 were SUPPRESSOR OF OVEREXPRESSION OF CONSTANS (SOC)-like; PpMADS9-1, PpMADS12-1, PpMADS14-1 and PpMADS16-1 were SEPALLATA (SEP)-like; while PpMADS15-1 was AGL/SHATTERPROOF (SHP)-like. Phylogenetic analysis showed their grouping into five major clades (and 10 sub-clades) that was consistent with their diverse functional types. Expression analysis in flower tissue revealed their distinct putative homeotic functional classes: A-class (PpMADS2-1, PpMADS3-1, PpMADS4-1, and PpMADS14-1), C-class (PpMADS15-1), E-class (PpMADS9-1, PpMADS12-1, and PpMADS16-1) and E (F)-class (PpMADS5-1 and PpMADS8-1). Differential gene expression was observed in different fruit tissues (skin, cortex and core) as well as in the cortex during the course of fruit development and ripening. Collectively, our results suggest their involvement in the diverse aspects of plant development including flower development and the course of fruit development and ripening.

Response of miR156-SPL Module during the Red Peel Coloration of Bagging-Treated Chinese Sand Pear (Pyrus pyrifolia Nakai)

MicroRNA156 is an evolutionarily highly conserved plant micro-RNA (miRNA) that controls an age-dependent flowering pathway. miR156 and its target SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes regulate anthocyanin accumulation in plants, but it is unknown whether this process is affected by light. Red Chinese sand pear (Pyrus pyrifolia) fruits exhibit a unique coloration pattern in response to bagging treatments, which makes them appropriate for studying the molecular mechanism underlying light-induced anthocyanin accumulation in fruit. Based on high-throughput miRNA and degradome sequencing data, we determined that miR156 was expressed in pear fruit peels, and targeted four SPL genes. Light-responsive elements were detected in the promoter regions of the miR156a and miR156ba precursors. We identified 19 SPL genes using the “Suli” pear (Pyrus pyrifolia Chinese White Pear Group) genome database, of which seven members were putative miR156 targets. The upregulated expression of anthocyanin biosynthetic and regulatory genes and downregulated expression of PpSPL2, PpSPL5, PpSPL7, PpSPL9, PpSPL10, PpSPL13, PpSPL16, PpSPL17, and PpSPL18 were observed in pear fruits after bags were removed from plants during the anthocyanin accumulation period. Additionally, miR156a/ba/g/s/sa abundance increased after bags were removed. Yeast two-hybrid results suggested that PpMYB10, PpbHLH, and PpWD40 could form a protein complex, probably involved in anthocyanin biosynthesis. Additionally, PpSPL10 and PpSPL13 interacted with PpMYB10. The results obtained in this study are helpful in understanding the possible role of miR156 and its target PpSPL genes in regulating light-induced red peel coloration and anthocyanin accumulation in pear.

Repression of TERMINAL FLOWER1 primarily mediates floral induction in pear (Pyrus pyrifolia Nakai) concomitant with change in gene expression of plant hormone-related genes and transcription factors

Repression of TERMINAL FLOWER1 primarily mediates floral induction in pear, and plant hormone-related genes and several transcription factors contribute to this.

Identification, classification, and transcription profiles of the B-type response regulator family in pear

Type-B response regulators (B-RRs) are transcription factors that function in the final step of two-component signaling systems. In model plants, B-RRs have been shown to play important roles in cytokinin signal transduction. However, the functions of B-RRs in pear have not been well studied. In this report, we conducted a genome-wide analysis and identified 11 putative genes encoding B-PpRR proteins based on the published genome sequence of Pyrus bretschneideri. A phylogenetic tree of the B-PpRR family was constructed, and the motif distribution, chromosome localization, and gene structure of B-PpRR family genes were determined. Gene transcript profiles, which were determined from transcriptome data, indicated that B-PpRR genes potentially function during pear fruit development, bud dormancy, and light/hormone-induced anthocyanin accumulation. Treatment of the fruitlets of ‘Cuiguan’ pear (Pyrus pyrifolia), which never accumulates anthocyanin, with the cytokinin N-(2-chloro-4-pyridyl)- N′-phenylurea (CPPU) clearly induced anthocyanin accumulation. Anthocyanins accumulated in the skin of fruitlets by 16 days after CPPU treatment, along with the significant activation of most anthocyanin biosynthetic genes. Analyses of B-PpRR transcript levels suggested that B-PpRR genes mediated this accumulation of anthocyanins. These findings enrich our understanding of the function of B-PpRR genes in the physiological processes of pear.

Abscisic Acid (ABA ) Promotes the Induction and Maintenance of Pear (Pyrus pyrifolia White Pear Group) Flower Bud Endodormancy

Dormancy is an adaptive mechanism that allows temperate deciduous plants to survive unfavorable winter conditions. In the present work, we investigated the possible function of abscisic acid (ABA) on the endodormancy process in pear. The ABA content increased during pear flower bud endodormancy establishment and decreased towards endodormancy release. In total, 39 putative genes related to ABA metabolism and signal transductions were identified from pear genome. During the para- to endodormancy transition, PpNCED-2 and PpNCED-3 had high expression levels, while PpCYP707As expression levels were low. However, during endodormancy, the expression of PpCYP707A-3 sharply increased with increasing cold accumulation. At the same time, the ABA content of pear buds declined, and the percentage of bud breaks rapidly increased. On the other hand, the expression levels of PpPYLs, PpPP2Cs, PpSnRK2s, and PpABI4/ABI5s were also changed during the pear flower bud dormancy cycle. Furthermore, exogenous ABA application to para-dormant buds significantly reduced the bud breaks and accelerated the transition to endodormancy. During the whole treatment time, the expression level of PpPP2C-12 decreased to a greater extent in ABA-treated buds than in control. However, the expression levels of PpSnRK2-1, PpSnRK2-4, and PpABI5-1 were higher in ABA-treated buds. Our results indicated that PpCYP707A-3 and PpNCEDs play pivotal roles on the regulation of endodormancy release, while ABA signal transduction pathway also appears to be involved in the process. The present work provided the basic information about the function of ABA-related genes during pear flower bud dormancy process.

PpHB22, a member of HD-Zip proteins, activates PpDAM1 to regulate bud dormancy transition in ‘Suli’ pear (Pyrus pyrifolia White Pear Group)

Homeodomain-leucine zipper (HD-Zip) proteins, which form one of the largest and most diverse families, regulate many biological processes in plants, including differentiation, flowering, vascular development, and stress signaling. Abscisic acid (ABA) has been proved to be one of the key regulators of bud dormancy and to influence several HD-Zip genes expression. However, the role of HD-Zip genes in regulating bud dormancy remains unclear. We identified 47 pear (P. pyrifolia White Pear Group) HD-Zip genes, which were classified into four subfamilies (HD-Zip I-IV). We further revealed that gene expression levels of some HD-Zip members were closely related to ABA concentrations in flower buds during dormancy transition. Exogenous ABA treatment confirmed that PpHB22 and several other HD-Zip genes responded to ABA. Yeast one-hybrid and dual luciferase assay results combining subcellular localization showed that PpHB22 was present in nucleus and directly induced PpDAM1 (dormancy associated MADS-box 1) expression. Thus, PpHB22 is a negative regulator of plant growth associated with the ABA response pathway and functions upstream of PpDAM1. These findings enrich our understanding of the function of HD-Zip genes related to the bud dormancy transition.

Genome-wide survey and analysis of the TIFY gene family and its potential role in anthocyanin synthesis in Chinese sand pear ( Pyrus pyrifolia )

The TIFY family is an important gene family which can be found only in plant and involved in different biologic processes. Jasmonic acid (JA) promotes anthocyanin accumulation in fruit. To explore the role of PpTIFY genes in anthocyanin biosynthesis of Chinese sand pear (Pyrus pyrifolia Nakai), we first cloned 21 PpTIFY genes from the pear genome and further identified 11 PpJAZ genes. The sequence similarity among the PpTIFY genes was relatively low, which indicated that PpTIFY genes in higher plants differentiated early during land plant evolution and have experienced considerable mutation. Transcripts of PpTIFY genes were detected in all organs and tissues of pear analyzed. The spatial and temporal expression patterns indicated that PpTIFY genes were associated with anthocyanin accumulation and JA signaling. The expression levels of PpTIFY genes were highest in leaves, whereas during fruit maturation, the expression level dramatically decreased. Furthermore, PpTIFY was induced after JA and light treatment in conjunction with anthocyanin accumulation in the peel of red fruit of Chinese sand pear. Genome-wide identification and characterization of pear PpTIFY genes will be helpful for further functional analysis of this gene family and cultivar improvement in pears.