Solanum lycopersicum cytokinin response factor (SlCRF)genes: characterization of CRF domain-containing ERF genes in tomato

Cytokinin is an influential hormone in growth and developmental processes across many plant species. While several cytokinin-regulated genes have been well characterized inArabidopsis, few have been identified in tomato,Solanum lycopersicum. Here a tomato family of 11 highly related cytokinin response factor genes designated asSlCRF1–SlCRF11 (Solanum lycopersicum cytokinin response factor)are identified and characterized.SlCRFs are AP2/ERF transcription factors and generally orthologous toArabidopsisCRF clade members (AtCRFs). SomeSlCRFgenes lack a directArabidopsisorthologue and oneSlCRF has a unique protein domain arrangement not seen in any other CRF protein. Expression analysis ofSlCRF1–SlCRF11revealed differential patterns and levels across plant tissues examined (leaf, stem, root and flower). SeveralSlCRFs show induction by cytokinin to various degrees, similar toAtCRFs. Additionally it is shown that someSlCRFs can be regulated by other factors, including NaCl, ethylene, methyl jasmonate, and salicylic acid. Examination ofSlCRF proteins in transientAgrobacteriuminfiltration experiments indicates they can be nuclear localizedin planta. Using a bimolecular fluorescence complementation (split-yellow fluorescent protein) system, it is also shown thatSlCRF proteins can interact to form homo- and heterodimers. Overall this work indicates that someSlCRFs resemble previously identified CRFs in terms of structure, expression, and cytokinin regulation. However,SlCRFs have novel CRF protein forms and responses to abiotic factors, suggesting they may have a diverse set of roles in stress and hormone regulation in tomato.