Direct Transcriptional Activation of LEHP2 and LEHP3 by LeMYB2 and LeMYB5 Underlies Postharvest Browning in Lentinus edodes

Postharvest shiitake mushrooms (Lentinus edodes) often undergo browning under low-temperature, high-humidity storage conditions, which significantly reduces their commercial value and constrains industry development. However, the molecular mechanisms regulating this process remain unclear. In this study, we used ‘Nongxiang No. 1’ as the experimental material and observed that during storage, the L* value of caps and stipes decreased continuously, shifting from light brown to dark brown-black. Concurrently, the relative electrical conductivity increased by approximately 3.07-fold, and the membrane lipid peroxidation product malondialdehyde (MDA) content increased by approximately 7.9-fold. Superoxide dismutase (SOD) activity initially increased then declined, indicating that elevated membrane permeability accelerates senescence. Peroxidase (POD) activity exhibited a significant upward then downward trend and improved 75.83% at day 22 of postharvest storage, with LEHP1, LEHP2, and LEHP3 gene expression patterns closely aligning with these changes. Specifically, LEHP2 and LEHP3 expression was upregulated by 23.8-fold and 2.35-fold on day 22 than day 0. Cis-element analysis identified MYB binding sites in all three LEHP genes. Genome-wide screening combined with qRT-PCR revealed two MYB transcription factors, LeMYB2 and LeMYB5, whose expression synchronized with LEHP genes. Transient expression assays in tobacco leaves confirmed their nuclear localization, consistent with transcription factor characteristics. Electrophoretic Mobility Shift Assay (EMSA) and Dual-Luciferase Reporter Assay (DLR) experiments further demonstrated that LeMYB2 and LeMYB5 directly activate LEHP2 and LEHP3 promoters, highlighting their key regulatory roles in postharvest browning of shiitake mushrooms.