Abstract
SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes, as unique plant transcription factors, play important roles in plant developmental regulation and stress response adaptation. Although mulberry is a commercially valuable tree species, there have been few systematic studies on SPL genes. In this work, we identified 15 full-length SPL genes in the mulberry genome, which were distributed on 4 Morus notabilis chromosomes. Phylogenetic analysis clustered the SPL genes from five plants (Malus × domestica Borkh, Populus trichocarpa, M. notabilis, Arabidopsis thaliana, and Oryza sativa) into five groups. Two zinc fingers (Zn1 and Zn2) were found in the conserved SBP domain in all of the MnSPLs. Comparative analyses of gene structures and conserved motifs revealed the conservation of MnSPLs within a group, whereas there were significant structure differences among groups. Gene quantitative analysis showed that the expression of MnSPLs had tissue specificity, and MnSPLs had much higher expression levels in older mulberry leaves. Furthermore, transcriptome data showed that the expression levels of MnSPL7 and MnSPL14 were significantly increased under silkworm herbivory. Molecular experiments revealed that MnSPL7 responded to herbivory treatment through promoting the transcription of MnTT2L2 and further upregulating the expression levels of catechin synthesis genes (F3′H, DFR, and LAR).
Highlights
SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes encode plant-specific transcription factors and are typified by highly conserved SQUAMOSA promoter-binding (SBP) domains
M. notabilis genome showed that 15 SPLs were unevenly distributed on 4 chromosomes, with 5 on Chr1 (SPL1, SPL3, SPL4, SPL8, and SPL10) and Chr2 (SPL2, SPL6, SPL7, SPL14, and SPL16B), 3 on Chr4 (SPL5, SPL15, and SPL16A), and 2 on Chr6 (SPL12 and SPL13)
This study found that mulberry SPL2, SPL10, and SPL15 were clustered into group 5 with AtSPL2, AtSPL9, AtSPL10, AtSPL11 and AtSPL15 in the phylogenetic tree (Figure 2) and were significantly expressed in the reproductive organs in mulberry (Figure 5)
Summary
SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes encode plant-specific transcription factors and are typified by highly conserved SQUAMOSA promoter-binding (SBP) domains. As unique plant transcription factors, SQUAMOSA PROMOTER BINDING PROTEINLIKE (SPL) genes play important roles in plant vegetative phase transition [12,13,14], flowering regulation [15,16], leaf morphogenesis [17], and root development [18,19,20]. SPL genes have a higher expression level in relatively more mature tissues. In Arabidopsis, the expression profiles of SPL genes increased as plants aged and were regulated by sequenceconserved microRNAs (miR156/157) [12,15,26,27]. AtSPL9 and AtSPL10, which were directly repressed by miR156/157, controlled the juvenile-to-adult phase transition [12]
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