Transcriptome and Resequencing Analyses Provide Insight into Differences in Organic Acid Accumulation in Two Pear Varieties

Specific physiological responses to alkaline carbonate stress in rice (Oryza sativa) seedlings: organic acid metabolism and hormone signalling

In recent years, alkaline soda soil has stimulated numerous biological research on plants under carbonate stress. Here, we explored the difference in physiological regulation of rice seedlings between saline (NaCl) and alkaline carbonate (NaHCO3 and Na2 CO3 ) stress. The rice seedlings were treated with 40mM NaCl, 40mM NaHCO3 and 20mM Na2 CO3 for 2h, 12h, 24h and 36h, their physiological characteristics were determined, and organic acid biosynthesis and metabolism and hormone signalling were identified by transcriptome analysis. The results showed that alkaline stress caused greater damage to their photosynthetic and antioxidant systems and led to greater accumulation of organic acid, membrane damage, proline and soluble sugar but a decreased jasmonic acid content compared with NaCl stress. Jasmonate ZIM-Domain (JAZ), the probable indole-3-acetic acid-amido synthetase GH3s, and the protein phosphatase type 2Cs that related to the hormone signalling pathway especially changed under Na2 CO3 stress. Further, the organic acid biosynthesis and metabolism process in rice seedlings were modified by both Na2 CO3 and NaHCO3 stresses through the glycolate/glyoxylate and pyruvate metabolism pathways. Collectively, this study provides valuable evidence on carbonate-responsive genes and insights into the different molecular mechanisms of saline and alkaline stresses.

Genome-wide identification, comparative analysis and functional roles in flavonoid biosynthesis of cytochrome P450 superfamily in pear (Pyrus spp.)

BACKGROUND

The cytochrome P450 (CYP) superfamily is the largest enzyme metabolism family in plants identified to date, and it is involved in many biological processes, including secondary metabolite biosynthesis, hormone metabolism and stress resistance. However, the P450 gene superfamily has not been well studied in pear (Pyrus spp.).

RESULTS

Here, the comprehensive identification and a comparative analysis of P450 superfamily members were conducted in cultivated and wild pear genomes. In total, 338, 299 and 419 P450 genes were identified in Chinese white pear, European pear and the wild pear, respectively. Based on the phylogenetic analyses, pear P450 genes were divided into ten clans, comprising 48 families. The motif and gene structure analyses further supported this classification. The expansion of the pear P450 gene family was attributed to whole-genome and single-gene duplication events. Several P450 gene clusters were detected, which have resulted from tandem and proximal duplications. Purifying selection was the major force imposed on the long-term evolution of P450 genes. Gene dosage balance, subfunctionalization and neofunctionalization jointly drove the retention and functional diversification of P450 gene pairs. Based on the association analysis between transcriptome expression profiles and flavonoid content during fruit development, three candidate genes were identified as being closely associated with the flavonoid biosynthesis, and the expression of one gene was further verified using qRT-PCR and its function was validated through transient transformation in pear fruit.

CONCLUSIONS

The study results provide insights into the evolution and biological functions of P450 genes in pear.

ABRE-BINDING FACTOR3-WRKY DNA-BINDING PROTEIN44 module promotes salinity-induced malate accumulation in pear

Malate impacts fruit acidity and plays a vital role in stress tolerance. Malate accumulation is induced by salinity in various plants as a metabolite in coping with this stress. However, the exact molecular mechanism responsible for salinity-induced malate accumulation remains unclear. Here, we determined that salinity treatment induces malate accumulation in pear (Pyrus spp.) fruit, calli, and plantlets compared to the control. Genetic and biochemical analyses established the key roles of PpWRKY44 and ABRE-BINDING FACTOR3 (PpABF3) transcription factors in promoting malate accumulation in response to salinity. We found that PpWRKY44 is involved in salinity-induced malate accumulation by directly binding to a W-box on the promoter of the malate-associated gene aluminum-activated malate transporter 9 (PpALMT9) to activate its expression. A series of in-vivo and in-vitro assays revealed that the G-box cis-element in the promoter of PpWRKY44 was targeted by PpABF3, which further enhanced salinity-induced malate accumulation. Taken together, these findings suggest that PpWRKY44 and PpABF3 play positive roles in salinity-induced malate accumulation in pears. This research provides insights into the molecular mechanism by which salinity affects malate accumulation and fruit quality.