Callus browning is a significant problem that hinders plant tissue regeneration in Paeonia ostii “Fengdan” by causing cell death and inhibiting growth. However, the molecular mechanism underlying callus browning in P. ostii remains unclear. In this study, we investigated the metabolites and potential regulatory genes involved in callus browning of P. ostii using metabolomic and transcriptomic analyses. We found a significant accumulation of phenolic compounds in the browned callus, represented by flavonoid compounds. Notably, the accumulations of luteotin and disomentin were higher in browning calli compared to non-browning calli. Transcriptomic analysis identified that candidate genes associated with flavonoid biosynthesis, including flavonoid 3-hydroxylase (PoF3H) and flavone synthase II (PoFNSII), were highly expressed in the browned callus of P. ostii “Fengdan”. Weighted gene co-expression network analysis (WGCNA) further highlighted that polyphenol oxidase (PoPPO) which encoded polyphenol oxidase, together with flavonoid biosynthesis-related genes such as flavanone 3-hydroxylase (PoF3H) and flavonone Synthase II (PoFNSII), as well as cellular totipotency-related genes wuschel-related homeobox 4 (PoWOX4), were involved in callus browning. Based on these findings, we proposed the molecular mechanism by which flavonoid accumulation, polyphenol oxidation, and cellular totipotency pathways contribute to callus browning in P. ostii. Our study provides new insights into the molecular mechanism underlying callus browning and offers the foundations to facilitate the establishment of an efficient plant tissue regeneration system in P. ostii.

The calla lily (Zantedeschia spreng.) is a bulbous flower native to the tropical regions of Africa. Calla lily has gained significant popularity in the international market owing to its intricate morphology and prolonged flowering duration. Despite such advantages, for two sub-groups of calla lily, known as group Zantedeschia and group Aestivae, there are challenges in terms of hybrid production due to the ‘plastome-genome incompatibility’ therebetween. Tissue culture is a fundamental biotechnological tool used in gene editing research, with a focus on disease resistance and flower color in calla lily breeding programs. The present review provides a brief background on the history and development of the calla lily, as well as a comprehensive and critical summary of calla lily tissue culture research. The regeneration pathways for both group Zantedeschia and group Aestivae can be divided into de novo organogenesis and somatic embryogenesis. Both groups are capable of obtaining replants through such means. However, only some species in group Aestivae have been reported to be successful in the somatic embryogenesis pathway. In the present review, special attention was paid to the influence of explant types, plant growth regulators, and culture conditions on both de novo organogenesis and somatic embryogenesis in calla lily tissue culture. Ultimately, future research prospects were determined based on integrated analysis of recent progress in calla lily tissue culture research.

Paeonia suffruticosa cv. ‘Yu Luo Chun’ is an important representative of the peony groups from the Jiangnan region of China. However, little is known about the genetic basis of chloroplast genome phylogeny and the adaptive evolution of this group. In this study, high-throughput sequencing technology was used to sequence the complete chloroplast genome of leaves, and sequence assembly, annotation and feature analysis were performed by bioinformatics analysis methods. The results showed that the chloroplast genome of P. suffruticosa cv. ‘Yu Luo Chun’ exhibited a typical tetrad structure with a total length of 152,596 bp, including a large single-copy (LSC) region, a small single-copy (SSC) region, and two inverted repeats (IRs) whose lengths were 84,272 bp, 17,044 bp and 25,640 bp, respectively. A total of 126 genes were annotated, including 85 protein-coding genes, 37 tRNA genes and 4 rRNA genes. Bioinformatics analysis showed that a total of 71 simple sequence repeats (SSRs) were searched in the chloroplast genome, of which the numbers of mononucleotide, dinucleotide, trinucleotide and tetranucleotide repeat motifs were 47, 12, 7 and 5, respectively, and no pentanucleotide or hexanucleotide repeat motifs were found. The chloroplast genome prefers to end in A/T, among which leucine (Leu) is the most frequently used, while cysteine ​​(Cys) is the least frequently used. Highly differentiated regions, such as rpoC1, petB, rsp16, rps19, clpP, ccsA, ycf1, ndhF-trnL, ndhD-psaC and trnV-rps12, were identified as DNA barcodes and potential genetic markers for interspecies relationships. We compared the gene selection pressure and identified 5 genes, ndhF, petB, petD, rpoA and ycf2 that were positively selected, and these genes have important contributions to the adaptive evolution. The chloroplast genome sequences of 18 species, including P. suffruticosa cv. ‘Yu Luo Chun’, were clustered by the nearest neighbour combination method and the maximum likelihood method. Both methods gave the same result and indicated that this cultivar has a relatively close kinship with P. qiui and P. rockii. The results provide important references for species identification, genetic diversity analysis and systematic taxonomic research between P. suffruticosa cv. ‘Yu Luo Chun’ and other Paeonia species.