The circadian-controlled PIF8-BBX28 module regulates petal senescence in rose flowers by governing mitochondrial ROS homeostasis at night.

Reactive oxygen species (ROS) are unstable reactive molecules that are toxic to cells. Regulation of ROS homeostasis is crucial to protect cells from dysfunction, senescence, and death. In plant leaves, ROS are mainly generated from chloroplasts and are tightly temporally restricted by the circadian clock. However, little is known about how ROS homeostasis is regulated in nonphotosynthetic organs, such as petals. Here, we showed that hydrogen peroxide (H2O2) levels exhibit typical circadian rhythmicity in rose (Rosa hybrida) petals, consistent with the measured respiratory rate. RNA-seq and functional screening identified a B-box gene, RhBBX28, whose expression was associated with H2O2 rhythms. Silencing RhBBX28 accelerated flower senescence and promoted H2O2 accumulation at night in petals, while overexpression of RhBBX28 had the opposite effects. RhBBX28 influenced the expression of various genes related to respiratory metabolism, including the TCA cycle and glycolysis, and directly repressed the expression of SUCCINATE DEHYDROGENASE 1, which plays a central role in mitochondrial ROS (mtROS) homeostasis. We also found that PHYTOCHROME-INTERACTING FACTOR8 (RhPIF8) could activate RhBBX28 expression to control H2O2 levels in petals and thus flower senescence. Our results indicate that the circadian-controlled RhPIF8-RhBBX28 module is a critical player that controls flower senescence by governing mtROS homeostasis in rose.

The Maternal Donor of Chrysanthemum Cultivars Revealed by Comparative Analysis of the Chloroplast Genome.

Chrysanthemum (Chrysanthemum morifolium Ramat) is an important floricultural crop and medicinal herb. Modern chrysanthemum cultivars have complex genetic backgrounds because of multiple cycles of hybridization, polyploidization, and prolonged cultivation. Understanding the genetic background and hybrid origin of modern chrysanthemum cultivars can provide pivotal information for chrysanthemum genetic improvement and breeding. By now, the origin of cultivated chrysanthemums remains unclear. In this study, 36 common chrysanthemum cultivars from across the world and multiple wild relatives were studied to identify the maternal donor of modern chrysanthemum. Chloroplast (cp) genomes of chrysanthemum cultivars were assembled and compared with those of the wild relatives. The structure of cp genomes was highly conserved among cultivars and wild relatives. Phylogenetic analyses based on the assembled cp genomes showed that all chrysanthemum cultivars grouped together and shared 64 substitutions that were distinct from those of their wild relatives. These results indicated that a diverged lineage of the genus Chrysanthemum, which was most likely an extinct or un-sampled species/population, provided a maternal source for modern cultivars. These findings provide important insights into the origin of chrysanthemum cultivars, and a source of valuable genetic markers for chrysanthemum breeding programs.

Complete chloroplast genome sequence of a Chinese traditional cultivar in Chrysanthemum, Chrysanthemum morifolium 'Anhuishiliuye'.

The complete plastid genome of Chrysanthemum morifolium 'Anhuishiliuye', a Chinese traditional cultivar, was determined and analyzed in this work. It had a circular-mapping molecular with the length of 151,059 bp.The LSC and SSC of 82,857 bp and 18,294 bp were separated by two IRs of 24,954 bp. The chloroplast genome of C. morifolium 'Anhuishiliuye' contains 125 genes, including 83 protein-coding genes, 34 ribosomal RNA genes and 8 transfer RNA genes. Phylogenetic analysis showed that C. morifolium 'Anhuishiliuye' clustered together with other Chrysanthemum species. The data provided would be useful for elucidation of phylogenetics and evolution in Chrysanthemum cultivars.

Complete chloroplast genome sequence of a Dutch cultivar of Chrysanthemum, Chrysanthemum morifolium 'Orizaba' (Asteraceae).

The complete plastid genome of Chrysanthemum morifolium 'Orizaba', a cultivar from Holland, was determined and analyzed in this work. It is a circular chromosome and has a length of 151,060 bp. The LSC and SSC of 82,858 bp and 18,294 bp were separated by two IRs of 24,954 bp. The chloroplast genome of C. morifolium 'Orizaba' contains 125 genes, including 83 protein-coding genes, eight ribosomal RNA genes, and 34 transfer RNA genes. Phylogenetic analysis showed that C. morifolium 'Orizaba' clustered together with other Chrysanthemum varieties in the family Asteraceae. The plastome is useful for the elucidation of phylogenetics and evolution in the Asteraceae and Chrysanthemum varieties.

RhWRKY33 Positively Regulates Onset of Floral Senescence by Responding to Wounding- and Ethylene-Signaling in Rose Plants.

Rose plants are one of the most important horticultural crops, whose commercial value mainly depends on long-distance transportation, and wounding and ethylene are the main factors leading to their quality decline and accelerated senescence in the process. However, underlying molecular mechanisms of crosstalk between wounding and ethylene in the regulation of flower senescence remain poorly understood. In relation to this, transcriptome analysis was performed on rose flowers subjected to various treatments, including control, wounding, ethylene, and wounding- and ethylene- (EW) dual treatment. A large number of differentially expressed genes (DEGs) were identified, ranging from 2,442 between the ethylene- and control-treated groups to 4,055 between the EW- and control-treated groups. Using weighted gene co-expression network analysis (WGCNA), we identified a hub gene RhWRKY33 (rchiobhmchr5g0071811), accumulated in the nucleus, where it may function as a transcription factor. Moreover, quantitative reverse transcription PCR (RT-qPCR) results showed that the expression of RhWRKY33 was higher in the wounding-, ethylene, and EW-treated petals than in the control-treated petals. We also functionally characterized the RhWRKY33 gene through virus-induced gene silencing (VIGS). The silencing of RhWRKY33 significantly delayed the senescence process in the different treatments (control, wounding, ethylene, and EW). Meanwhile, we found that the effect of RhWRKY33-silenced petals under ethylene and EW dual-treatment were stronger than those under wounding treatment in delaying the petal senescence process, implying that RhWRKY33 is closely involved with ethylene and wounding mediated petal senescence. Overall, the results indicate that RhWRKY33 positively regulates the onset of floral senescence mediated by both ethylene and wounding signaling, but relies heavily on ethylene signaling.

Erratum: Author Correction: RhMYB108, an R2R3-MYB transcription factor, is involved in ethylene- and JA-induced petal senescence in rose plants.

[This corrects the article DOI: 10.1038/s41438-019-0221-8.].

RhMYB108, an R2R3-MYB transcription factor, is involved in ethylene- and JA-induced petal senescence in rose plants.

Rose (Rosa hybrida) plants are major ornamental species worldwide, and their commercial value greatly depends on their open flowers, as both the quality of fully open petals and long vase life are important. Petal senescence can be started and accelerated by various hormone signals, and ethylene is considered an accelerator of petal senescence in rose. To date, however, the underlying mechanism of signaling crosstalk between ethylene and other hormones such as JA in petal senescence remains largely unknown. Here, we isolated RhMYB108, an R2R3-MYB transcription factor, which is highly expressed in senescing petals as well as in petals treated with exogenous ethylene and JA. Applications of exogenous ethylene and JA markedly accelerated petal senescence, while the process was delayed in response to applications of 1-MCP, an ethylene action inhibitor. In addition, silencing of RhMYB108 alter the expression of SAGs such as RhNAC029, RhNAC053, RhNAC092, RhSAG12, and RhSAG113, and finally block ethylene- and JA-induced petal senescence. Furthermore, RhMYB108 was identified to target the promoters of RhNAC053, RhNAC092, and RhSAG113. Our results reveal a model in which RhMYB108 functions as a receptor of ethylene and JA signals to modulate the onset of petal senescence by targeting and enhancing senescence-associated gene expression.

[The allozyme analysis of the genetic differentiation in self-inbred early generations of Lilium formolongi Hort].

The genetic diversity and differentiation of Lilium formolongi Hort. lines in self-inbred early generations were studied by allozyme electrophoresis. The results showed that mean allele number/locus, percentage of polymorphic loci, average observed heterozygosity and average expected heterozygosity were decreased with the increment of self-inbred generations. The purified loci, purified speed, fixed alleles and increment of genetic differentiation were different among lines because of selection and self-inbred. The mean genetic distances among F4 lines were larger than that of F3 lines, serving as another evidence to prove the differentiation among lines.