Abstract
The protein encoded by the TERMINAL FLOWER1 (TFL1) gene maintains indeterminacy in inflorescence meristem to repress flowering, and has undergone multiple duplications. However, basal angiosperms have one copy of a TFL1-like gene, which clusters with eudicot TFL1/CEN paralogs. Functional conservation has been reported in the paralogs CENTRORADIALIS (CEN) in eudicots, and ROOTS CURL IN NPA (RCNs) genes in monocots. In this study, long-term functional conservation and selective constraints were found between angiosperms, while the relaxation of selective constraints led to subfunctionalisation between paralogs. Long intron lengths of magnoliid TFL1-like gene contain more conserved motifs that potentially regulate TFL1/CEN/RCNs expression. These might be relevant to the functional flexibility of the non-duplicate TFL1-like gene in the basal angiosperms in comparison with the short, lower frequency intron lengths in eudicot and monocot TFL1/CEN/RCNs paralogs. The functionally conserved duplicates of eudicots and monocots evolved according to the duplication-degeneration-complementation model, avoiding redundancy by relaxation of selective constraints on exon 1 and exon 4. These data suggest that strong purifying selection has maintained the relevant functions of TFL1/CEN/RCNs paralogs on flowering regulation throughout the evolution of angiosperms, and the shorter introns with radical amino acid changes are important for the retention of paralogous duplicates.
Highlights
TERMINAL FLOWER1 (TFL1) is a member of the phosphatidylethanolamine-binding protein (PEBP) family
These functionally conserved paralogous gene duplicates may be subject to strong purifying selection pressures that constrain redundant functions, such as the floral-regulatory paralogs SEPALLATA 1 (SEP1) and SEPALLATA 2 (SEP2), and SHATTERPROOF 1 (SHP1) and SHATTERPROOF 2 (SHP2)[38]
One copy for each Magnoliid species was obtained after amplification, and this result is consistent with only one TFL1/CEN/ RCNs member in EST-library of basal angiosperm database
Summary
TERMINAL FLOWER1 (TFL1) is a member of the phosphatidylethanolamine-binding protein (PEBP) family. Different expression patterns of duplicated TFL1/CEN/RCNs genes in Arabidopsis[16], apple[17], tomato[18,19], and tobacco[20] tissues have been reported Such differential expression was suggested as complementary functions (subfunctionalisation)[21,22]. There have been limited studies focussed on the effects of selective pressures on TFL1/CEN/RCNs paralog duplication, as well as the TFL1-like gene in basal angiosperms. These functionally conserved paralogous gene duplicates may be subject to strong purifying selection pressures that constrain redundant functions, such as the floral-regulatory paralogs SEPALLATA 1 (SEP1) and SEPALLATA 2 (SEP2), and SHATTERPROOF 1 (SHP1) and SHATTERPROOF 2 (SHP2)[38]. Selective constraints may be important in functionally redundant paralogous genes for buffering an organism’s phenotype against deleterious mutations[39]
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