Identification and analysis of major latex protein (MLP) family genes in Rosa chinensis responsive to Botrytis cinerea infection by RNA-seq approaches

Roses (<i>Rosa chinensis</i>) are among the most cherished ornamental plants globally, yet they are highly susceptible to infections by <i>Botrytis cinerea</i>, the causative agent of gray mold disease. Here we inoculated the resistant rose variety 'Yellow Leisure Liness' with <i>B. cinerea</i> to investigate its resistance mechanisms against gray mold disease. Through transcriptome sequencing, we identified 578 differentially expressed genes (DEGs) that were significantly upregulated at 24, 48, and 72 hours post-inoculation, with these genes significantly enriched for three defense response-related GO terms. Further domain analysis of the genes in these GO terms reveal that 21 DEGs contain the Bet v 1 family domain, belonging to the major latex protein (<i>MLP</i>) gene family, suggesting their potential key role in rose disease resistance. Furthermore, we systematically identified 46 <i>RcMLP</i> genes in roses and phylogenetically categorized them into two distinct subfamilies: group I and II. Genomic duplication analysis indicates that tandem duplication is the main driver for the expansion of the <i>RcMLP</i> family, and these genes have undergone by purifying selection. Additionally, detailed analyses of gene structure, motif composition, and promoter regions reveal that <i>RcMLP</i> genes contain numerous stress-responsive elements, with 32 <i>RcMLP</i> genes harboring fungal elicitor/wound-responsive elements. The constructed potential transcription factor regulatory network showed significant enrichment of the ERF transcription factor family in the regulation of <i>RcMLP</i> genes. Gene expression analysis reveal that DEGs are mainly distributed in subfamily II, where four highly expressed genes (<i>RcMLP13</i>, <i>RcMLP28</i>, <i>RcMLP14</i>, and <i>RcMLP27</i>) are identified in a small branch, with their fold change exceeding ten folds and verified by qRT-PCR. In summary, our research results underscore the potential importance of the <i>RcMLP</i> gene family in response to <i>B. cinerea</i> infection and provide comprehensive basis for further function exploration of the <i>MLP</i> gene family in rose resistance to fungal infections.