LcMYB306 regulates litchi fruit water loss and browning by inhibiting the expression of LcPIP2;4

Pericarp browning of postharvest litchi is a significant obstacle to the industry's high-quality development. Water loss from the pericarp is a key factor triggering browning, but the regulatory mechanism of water metabolism and its relationship with browning remain unclear. In this study, we found that aquaporin activity inhibitors (HgCl₂) can delay both water loss and browning in litchi. LcPIP2;4, a plasma membrane intrinsic protein (PIP) family member exhibiting high expression in the litchi pericarp and the greatest water transport activity, is significantly downregulated during water loss and browning. Further analysis revealed that HgCl₂ suppresses both the expression and water transport activity of LcPIP2;4, indicating a close association with the observed browning phenotype. By constructing transient overexpression fruits and transgenic callus tissues of LcPIP2;4 and measuring the water loss rate and browning index, we confirmed that LcPIP2;4 positively regulates water loss and browning in litchi. Through weighted gene co-expression network, LcPIP2;4 promoter sequence, and Quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR) analysis, we identified 10 potential interacting transcription factors. Yeast one-hybrid, dual-luciferase reporter assay, chromatin immunoprecipitation analysis, and electrophoretic mobility shift assay confirmed that LcMYB306 specifically binds to the LcPIP2;4 promoter. In LcMYB306 overexpressing fruits and embryogenic callus, LcPIP2;4 expression was suppressed, resulting in delayed water loss and browning. In contrast, in CRISPR/Cas9-edited LcMYB306 callus, LcPIP2;4 expression was upregulated, and water loss and browning were accelerated, confirming that LcMYB306 negatively regulates this process. This study demonstrates that LcMYB306 delays postharvest water loss and browning in litchi by repressing LcPIP2;4 transcriptionally expression. It provides a theoretical foundation and key target gene for developing litchi varieties resistant to browning.