Overexpression of AtCSP4 affects late stages of embryo development in Arabidopsis

Eukaryotic cold shock domain proteins are nucleic acid-binding proteins that are involved in transcription, translation via RNA chaperone activity, RNA editing, and DNA repair during tissue developmental processes and stress responses. Cold shock domain proteins have been functionally implicated in important developmental transitions, including embryogenesis, in both animals and plants. Arabidopsis thaliana cold shock domain protein 4 (AtCSP4) contains a well conserved cold shock domain (CSD) and glycine-rich motifs interspersed by two retroviral-like CCHC zinc fingers. AtCSP4 is expressed in all tissues but accumulates in reproductive tissues and those undergoing cell divisions. Overexpression of AtCSP4 reduces silique length and induces embryo lethality. Interestingly, a T-DNA insertion atcsp4 mutant does not exhibit any morphological abnormalities, suggesting that the related AtCSP2 gene is functionally redundant with AtCSP4. During silique development, AtCSP4 overexpression induced early browning and shrunken seed formation beginning with the late heart embryo stage. A 50% segregation ratio of the defective seed phenotype was consistent with the phenotype of endosperm development gene mutants. Transcripts of FUS3 and LEC1 genes, which regulate early embryo formation, were not altered in the AtCSP4 overexpression lines. On the other hand, MEA and FIS2 transcripts, which are involved in endosperm development, were affected by AtCSP4 overexpression. Additionally, AtCSP4 overexpression resulted in up-regulation of several MADS-box genes (AP1, CAL, AG, and SHP2) during early stages of silique development. Collectively, these data suggest that AtCSP4 plays an important role during the late stages of silique development by affecting the expression of several development-related genes.