| The 14-3-3 proteins associate with a vast number of client proteins, allowing for numerous roles in eukaryotic pathways. The versatility of 14-3-3 interactions is based on the fact that 14-3-3 proteins bind to canonical binding motifs, which are found in thousands of proteins. In addition, most eukaryotes express multiple 14-3-3 isoforms, each having slightly different protein sequences, which most likely increases the number of 14-3-3 client proteins. For instance, arabidopsis contains thirteen expressed 14-3-3 genes. The study of isoform-specific 14-3-3 functions may help categorize the roles of 14-3-3 proteins. In arabidopsis, a convenient way to study individual 14-3-3 isoforms, is to analyze 14-3-3 T-DNA insertion mutants. Arabidopsis T-DNA insertion mutant lines were characterized for a deficiency in expression of individual 14-3-3 isoforms. Flowering timing, root development and chloroplast development were closely studied in T-DNA insertion mutants altered in 14-3-3 upsilon or micro protein expression. The T-DNA insertion mutants altered in 14-3-3 upsilon or micro expression exhibited both a delay in transition to flowering and reduced sensitivity in red light perception during early development. In addition, T-DNA insertion mutants altered in 14-3-3 micro expression exhibited shorter root lengths, increased chlorophyll synthesis in leaf tissue, increased numbers of chloroplasts in the roots during early development and reduced chloroplast numbers in the root after ten days of growth. Data collected from the phenotypic studies of 14-3-3 T-DNA insertion mutants were combined with biochemical assays to reveal relationships between 14-3-3, CONSTANS (CO) and phytochrome B (PHYB) proteins in flowering timing, root development, and chloroplast development pathways. In addition to 14-3-3 upsilon and micro, 14-3-3 T-DNA insertion mutants for several other 14-3-3 isoforms were assayed for phenotypes exhibited by 14-3-3 upsilon and micro T-DNA insertion mutants and also for excessive starch accumulation, as exhibited by 14-3-3 antisense mutants. The presented study characterizes isoform-specific roles of 14-3-3 proteins in several biological pathways of arabidopsis, which adds further resolution to the importance of both general 14-3-3 protein function and the function of individual 14-3-3 isoforms. |
