Summary: Plant with naturally twisted branches is referred to as a tortuous‐branch plant, which have extremely high ornamental value due to their zigzag shape and the natural twisting of their branches. Prunus mume is an important woody ornamental plant. However, the molecular mechanism underlying this unique trait in Prunus genus is unknown. Here, we present a chromosome‐level genome assembly of the cultivated P. mume var. tortuosa created using Oxford Nanopore combined with Hi‐C scaffolding, which resulted in a 237.8 Mb genome assembly being anchored onto eight pseudochromosomes. Molecular dating indicated that P. mume is the most recently differentiated species in Prunus. Genes associated with cell division, development and plant hormones play essential roles in the formation of tortuous branch trait. A putative regulatory pathway for the tortuous branch trait was constructed based on gene expression levels. Furthermore, after transferring candidate PmCYCD genes into Arabidopsis thaliana, we found that seedlings overexpressing these genes exhibited curled rosette leaves. Our results provide insights into the evolutionary history of recently differentiated species in Prunus genus, the molecular basis of stem morphology, and the molecular mechanism underlying the tortuous branch trait and highlight the utility of multi‐omics in deciphering the properties of P. mume plant architecture.

Single-flower cut Chrysanthemum (Dendranthema grandiflorum ‘Jinba’) holds a unique status in global floriculture industry. However, the extensive axillary bud outgrowth presents a major drawback. Shade is an environment cue that inhibits shoot branching. Present study was aimed at investigating the effect of ratio of red to far-red light (R:FR) in regulating the lateral bud outgrowth of Chrysanthemum and the detailed mechanism. Results showed that the fate of axillary buds at specific positions in stem exhibited difference in response to R:FR. Decreasing R:FR resulted in elevation of abscisic acid (ABA) accumulation in axillary buds. Expression of ABA, indole-3-acetic acid (IAA) and strigolactones (SL) -related metabolism and signal transduction genes was significantly changed in response to low R:FR. In addition, low R:FR caused the re-distribution of sucrose across the whole plant, driving more sucrose towards bottom buds. Our results indicate that low R:FR not always inhibits bud outgrowth, rather its influence depends on the bud position in the stem. ABA, SL and auxin pathways were involved in the process. Interestingly, sucrose also appears to be involved in the process which is necessary to pay attention in the further studies. The present study also lays the foundation for developing methods to regulate axillary bud outgrowth in Chrysanthemum.

Chrysanthemum (Dendranthema grandiflorum cv. Jinba) shoot branching is determined by bud outgrowth during the vegetative growth stage. The degree of axillary bud outgrowth is highly influenced by environmental conditions, such as nutrient availability. Here, we demonstrated that phosphorus (Pi) starvation significantly reduces axillary bud outgrowth in chrysanthemum. A strigolactone (SL) biosynthesis gene, DgCCD7, was isolated and characterized as an ortholog of MAX3/DAD3/RMS5/D17. By using ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS), three putative SLs were identified and detected strong induction under Pi starvation conditions. Determinations of the distribution of SLs and negative regulation of DgCCD7/8 time-course in root indicated systemic response of SL. However, temporal expression patterns of biosynthesis and signaling genes in nodes revealed that Pi starvation causes a local response of SL pathway. Application of modified node segments treated with or without auxin and Pi revealed that in the absence of exogenous auxin, Pi delay axillary buds outgrowth and up-regulating local SL pathway genes. These data indicate that an auxin-SL regulatory loop respond to Pi starvation for delaying bud outgrowth locally, root biosynthesized SLs are transported acropetally and function in shoot branching inhibition under Pi starvation. We propose that SLs contribute to chrysanthemum shoot branching control in response to Pi-limiting conditions in a systemic way.

Transcription factors encoded by the three-amino-acid-loop-extension (TALE) gene family play a key role in regulating plant growth and development, and are involved in plant hormone regulatory pathways and responses to various environmental stresses. Researchers are currently studying TALE genes in different species, but Prunus mumeTALE genes have not yet been studied. Therefore, based on the P. mume genome, we found a total of 23 TALE gene family members, which were distributed on eight chromosomes. TALE genes contained the characteristic domains of this family, and could be divided into KNOTTED-like homeobox (KNOX) subfamily and BEL1-like homeobox (BELL) subfamily. They can form heterodimers with each other. Fragment duplication and tandem duplication events were the main reasons for the expansion of P. mumeTALE gene family members and the TALE genes were selected by different degrees of purification. The inter-species collinearity analysis showed that the relationship between P. mume and other four Prunus species was consistent with the distance of origin. Eleven members of P. mumeTALE genes were specifically highly expressed in stem, mainly at the early stage of stem development. The cis-element analysis showed that the promoter of P. mumeTALE genes contained a variety of hormone and abiotic stress response elements, and four TALE genes responded to two kinds of abiotic stresses and four kinds of hormones at the early stage of stem development. In conclusion, this study lays a foundation to explore the role of TALE gene family in P. mume growth and development.

Chrysanthemum morifolium is a gynomonoecious plant that bears both female zygomorphic ray florets and bisexual actinomorphic disc florets in the inflorescence. This sexual system is quite prevalent in Asteraceae, but poorly understood. CYCLOIDEA (CYC) 2 subclade transcription factors, key regulators of flower symmetry and floret identity in Asteraceae, have also been speculated to function in reproductive organs and could be an entry point for studying gynomonoecy. However, the molecular mechanism is still unclear. On the other hand, the Arabidopsis WUSCHEL (WUS) transcription factor has been proven to play a vital role in the development of reproductive organs. Here, a WUS homologue (CmWUS) in C. morifolium was isolated and characterized. Overexpression of CmWUS in A. thaliana led to shorter siliques and fewer stamens, which was similar to CYC2-like genes reported before. In addition, both CmWUS and CmCYC2 were highly expressed in flower buds during floral organ differentiation and in the reproductive organs at later development stages, indicating their involvement in the development of reproductive organs. Moreover, CmWUS could directly interact with CmCYC2d. Thus, our data suggest a collaboration between CmWUS and CmCYC2 in the regulation of reproductive organ development in chrysanthemum and will contribute to a further understanding of the gynomonoecious sexual system in Asteraceae.

Pollen donor compositions differ during the early stages of reproduction due to various selection mechanisms. In addition, ovules linearly ordered within a fruit have different probabilities of reaching maturity. Few attempts, however, have been made to directly examine the magnitude and timing of selection, as well as the mechanisms during early life stages and within fruit. Robinia pseudoacacia, which contains linear fruit and non-random ovule maturation and abortion patterns, has been used to study the viability of selection within fruit and during the early stages of reproduction. To examine changes in the pollen donor composition during the early stages of reproduction and of progeny originating from different positions within fruit, paternity analyses were performed for three early life stages (aborted seeds, mature seeds and seedlings) in the insect-pollinated tree R. pseudoacacia.