Functional Characterization of MaSPL8 Reveals Its Different Roles in Biotic and Abiotic Stress Responses in Mulberry

The Squamosa promoter-binding protein-like (SPL) family proteins plays pivotal roles in plant development and stress adaptation. In this study, we functionally characterized <i>MaSPL8</i> in mulberry (<i>Morus alba</i>) and investigated its regulatory roles in biotic and abiotic stress responses. <i>MaSPL8</i> encodes a 364-amino acid protein with a conserved SBP domain and lacks <i>miR156/157</i> binding sites. Phylogenetic analysis confirmed its orthology to <i>Arabidopsis</i> AtSPL8, albeit with functional divergence. Downregulation of <i>MaSPL8</i> via virus-induced gene silencing (VIGS) resulted in more susceptibility to <i>Ciboria shiraiana</i> infection, but significantly enhanced resistance to drought and salt stress, as evidenced by reduced oxidative damage, elevated proline accumulation, and increased antioxidant enzyme activities. Transcriptomic profiling of <i>MaSPL8</i>-silenced plants revealed enrichment of differentially expressed genes (DEGs) in brassinosteroid biosynthesis, jasmonic acid metabolism, and oxidative stress responses, suggesting hormone signaling interplay. Furthermore, bioinformatic predictions identified <i>miR5658</i> and <i>miR4221</i> as potential post-transcriptional regulators of <i>MaSPL8</i>. This study highlights <i>MaSPL8</i> as a negative regulator of abiotic stress tolerance and positive regulator of biotic (<i>C. shiraiana</i>) stress tolerance in mulberry and provides insights into its integration with phytohormone pathways. Our findings underscore the evolutionary plasticity of <i>SPL8</i> genes and propose <i>MaSPL8</i> as a target for enhancing mulberry's resilience in challenging environments.