Rosa beggeriana ‘Aurea’ is a yellow-green leaf (yl) mutant and originated from Rosa beggeriana Schrenk by 60Co-γ irradiation, which is an important ornamental woody species. However, the molecular mechanism of the yl mutant remains unknown. Herein, comparative transcriptome profiling was performed between the yl type and normal green color type (WT) by RNA sequencing. A total of 3,372 significantly differentially expressed genes (DEGs) were identified, consisting of 1,585 upregulated genes and 1,787 downregulated genes. Genes that took part in metabolic of biological process (1,090), membrane of cellular component (728), catalytic (1,114), and binding of molecular function (840) were significantly different in transcription level. DEGs involved in chlorophyll biosynthesis, carotenoids biosynthesis, cutin, suberine, wax biosynthesis, photosynthesis, chloroplast development, photosynthesis-antenna proteins, photosystem I (PSI) and photosystem II (PSII) components, CO2 fixation, ribosomal structure, and biogenesis related genes were downregulated. Meanwhile, linoleic acid metabolism, siroheme biosynthesis, and carbon source of pigments biosynthesis through methylerythritol 4-phosphate (MEP) pathways were upregulated. Moreover, a total of 147 putative transcription factors were signification different expression, involving NAC, WRKY, bHLH, MYB and AP2/ERF, C2H2, GRAS, and bZIP family gene. Our results showed that the disturbed pigments biosynthesis result in yl color by altering the ratio of chlorophylls and carotenoids in yl mutants. The yl mutants may evoke other metabolic pathways to compensate for the photodamage caused by the insufficient structure and function of chloroplasts, such as enhanced MEP pathways and linoleic acid metabolism against oxidative stress. This research can provide a reference for the application of leaf color mutants in the future.

Sugars Will Eventually be Exported Transporter (SWEET) gene family plays indispensable roles in plant physiological activities, development processes, and responses to biotic and abiotic stresses, but no information is known for roses. In this study, a total of 25 RcSWEET genes were identified in Rosa chinensis ‘Old Blush’ by genome-wide analysis and clustered into four subgroups based on their phylogenetic relationships. The genomic features, including gene structures, conserved motifs, and gene duplication among the chromosomes of RcSWEET genes, were characterized. Seventeen types of cis-acting elements among the RcSWEET genes were predicted to exhibit their potential regulatory roles during biotic and abiotic stress and hormone responses. Tissue-specific and cold-response expression profiles based on transcriptome data showed that SWEETs play widely varying roles in development and stress tolerance in two rose species. Moreover, the different expression patterns of cold-response SWEET genes were verified by qRT-PCR between the moderately cold-resistant species R. chinensis ‘Old Blush’ and the extremely cold-resistant species R. beggeriana. Especially, SWEET2a and SWEET10c exhibited species differences after cold treatment and were sharply upregulated in the leaves of R. beggeriana but not R. chinensis ‘Old Blush’, indicating that these two genes may be the crucial candidates that participate in cold tolerance in R. beggeriana. Our results provide the foundation for function analysis of the SWEET gene family in roses, and will contribute to the breeding of cold-tolerant varieties of roses.