Dissecting SEPALLATA3 Splicing Variant Functions During Arabidopsis Vegetative Growth by amiRNA Technology

SEPALLATA (SEP) genes encode E-class floral homeotic transcriptional factors involved in regulation of flowering. In the present work, artificial microRNA (amiRNA) technology was adopted to downregulate the expression levels of SEP3-2, SEP3-3 and SEP4. Silencing of SEP3-2 and SEP3-3 did not generate obvious phenotypic changes in the four types of floral organs. However, knockdown of SEP3-2 and SEP3-3 resulted in suppression of FLOWERING LOCUS T (FT) and GIGANTEA (GI), accompanied by a delay in flowering time. SEP3-2 can directly bind to CArG-boxes existing in the promoter of AGL17, AGL20, AGL42, CCA1, FT, TCP3, TCP12, while SEP3-3 can directly interact with CArG-boxes existing in the promoter of AGL15, AGL24, CUC2, MAF5 and TCP2, indicating the encoded products of two alternative splicing variants of SEP3 can affect distinct target genes. These results suggest that SEP3-2 and SEP3-3 are probably involved in controlling different developmental processes. Compared to wild-type plants, the vegetative growth of amiRNA-SEP3-2 and amiRNA-SEP3-3 transgenic plants was more vigorous, and the morphology of leaves was changed significantly, including a widening the blade, increased surface area, longer petiole and serrated margin. In amiRNA-SEP4 transgenic plants, sepals were converted into petaloid structures, and the number of floral organs in the outside three whorls was reduced. In addition, amiRNA-SEP4 transgenic plants presented a late-flowering phenotype, illustrating the important roles of SEP4 in floral transition. These results showed that SEP3-2 and SEP3-3, two splicing variants of SEP3, involved in morphogenesis of leaves and floral organ development by conferring transcriptional activity. Moreover, SEP4 genes participate in development of sepals, petals, stamens and carpels. All these results indicated that SEPALLATA genes of Arabidopsis possessed diversified functions. In addition to the roles in reproductive growth, these genes can also influence the vegetative growth.

Automated summary

The study revealed the important role of SEPALLATA genes in regulating flowering, leaf morphology and floral organ development in Arabidopsis. Two splicing variants, SEP3-2 and SEP3-3, of SEP3 gene were found to be involved in leaf morphogenesis and floral organ development by affecting transcriptional activity. SEP4 genes participate in the development of sepals, petals, stamens, and carpels. These findings demonstrate the diversified functions of SEPALLATA genes.