Edible and medicinal fungi are renowned for their high nutritional value, as they are rich in essential amino acids, proteins, dietary fiber, vitamins, and minerals [1]. These fungi also have a distinct flavor and contain a diverse range of bioactive compounds, such as polysaccharides, terpenoids, alkaloids, steroids, and polyphenols, all of which are benefits to human health [1,2]. Notable examples include Ganoderma lucidum [3], Cordyceps sinensis [4], and Sanghuangporus sanghuang [5], among others. However, as public awareness of health and wellness improves, edible and medicinal fungi have attracted increasing attention, and more and more species have been involved in related studies.

Of the underestimated edible and medicinal fungi, Laetiporus has a great potential to be mined. Laetiporus is a wood-rotting basidiomycetous fungal genus with fleshy texture. This genus belongs to the family Laetiporaceae, the order Polyporales within the class Agaricomycetes. The species of Laetiporus typically grow on decaying logs, stumps, and trunks of both deciduous and coniferous trees, and are widely distributed around Europe, North America, Africa, and Asia [[6], [7], [8]]. In Asia, certain species of Laetiporus have been traditionally used for both culinary and medicinal purposes for a long time [9]. Recently, extensive researches have focused on the bioactive compounds derived from Laetiporus, especially from the generic type L. sulphureus, which can be broadly categorized into macromolecules, such as polysaccharides and lectins, and small molecules, including sterols, triterpenes, sesquiterpenes, polyenes and volatile compounds [9]. These compounds endow Laetiporus with notable biological activities, such as antimicrobial [10,11], antioxidant [12], anti-inflammatory [13], anticancer, and immunomodulatory properties [14].

Polysaccharides are the most abundant bioactive compounds, and mainly located in the cell wall of Laetiporus as polymeric carbohydrates [15,16]. In recent years, the polysaccharides in Laetiporus have received increasing attention due to their potential bioactivities, including anticancer [17], antioxidant [18], hypoglycemic [19], hepatoprotective [20] and antitumor [21] properties. These properties are largely attributed to the presence of β-glucans, often characterized by (1 → 3) linkages [15]. Nevertheless, significant gaps remain in understanding the biosynthetic pathway of polysaccharides in Laetiporus, especially the dynamic regulation of the key genes, enzymes and metabolites involved in the pathway throughout the mycelial growth period. This knowledge gap restricts the development of genetic engineering strains for the targeted production of polysaccharides.

Polysaccharide biosynthesis involves complex metabolic networks that are fine regulated by a series of enzymatic reactions catalyzed by invertase (INV/sacA), hexokinase (HK), fructokinase (scrK), glycosyltransferases (GTs) and so on [22]. The pathway begins with the conversion of sucrose into glucose (Glc) and fructose (Fru) catalyzed by INV/sacA. Subsequently, HK and scrK further phosphorylate glucose and fructose to glucose-6-phosphate (Glc-6-P) and fructose-6-phosphate (Fru-6-P), respectively. These phosphorylated monosaccharides are subsequently utilized to synthesize uridine diphosphate glucose (UDP-Glc) and guanosine diphosphomannose (GDP-Man), which are then polymerized into polysaccharides through glycosyltransferase (GT)-mediated reactions [[22], [23], [24], [25]]. Furthermore, with the advancement of high-throughput sequencing technology, recent studies have employed RNA sequencing (RNA-seq) method to reveal the expression patterns of genes involved in the polysaccharide biosynthesis, and identified several key genes and related molecular mechanisms [26,27]. More importantly, multiomics technology can help to provide a more comprehensive understanding of the complex processes in the polysaccharide biosynthesis pathway [23,28,29]. The researches on the polysaccharide biosynthesis pathway in plants are more completely, and provide an essential theoretical and methodological reference for revealing the similar biosynthetic process in edible and medicinal fungi, including Laetiporus.

Within the genus Laetiporus, L. sulphureus has been the most extensively studied from the medicinal perspective. However, additional species also deserve more attention, especially the East Asian endemic species L. cremeiporus [30], which has been reported to possess significant antioxidant activity and thus high pharmacological potential [31,32]. In this study, based on the newly generated high-quality reference genome of L. cremeiporus, the metabolome and transcriptome of the mycelia sampled at four growth periods were integratively analyzed. In association with the activity analysis of the key enzymes related to the polysaccharide biosynthesis, the multiomics data reveal the metabolic profile of polysaccharides and identify key genes involved in the biosynthesis pathways of polysaccharides.