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   HOME > Faculty & Staff > Faculty > Williams > Williams Research

Mary E. Williams
Research

The sac9-1 Mutant of Arabidopsis thaliana

The sac9-1 mutant in Arabidopsis thaliana is slow growing and dwarfed (Fig. 1).
 Columbia and sac9-1 plants in pots
Figure 1. Wild-type Columbia strain of Arabidopsis thaliana (left) and the sac9-1 mutant (right).
Guard cells in sac9 mutants are flaccid, and epidermal cells accumulate purple anthocyanin (Figure 2) Columbia and sac9-1 guard cells
Figure 2. Guard cells of the wild-type Columbia strain of Arabidopsis thaliana (left) and the sac9-1 mutant (right).
The sac9 phenotype can be mimicked by subjecting wild-type plants to osmotic stress (Figure 3).
 Roots of Columbia and sac9-1 plants grown with or without NaCl
Figure 3. Ten-day-old plants of wild-type Columbia strain of Arabidopsis thaliana grown with (left) or without (middle) 50 mM NaCl and the sac9-1 mutant grown without NaCl (right).
The SAC9 gene encodes a putative phosphoinositide phosphatase (PI phosphatase) and the plants accumulate PtdIns(4,5)P2 and Ins(1,4,5)P3:
Enzymes involved in production of phosphoinosotide phosphates
Accumulation of PtdIns(4,5)P2 in yeast causes an increased rate of endocytosis; using the lipid-binding dye FM4-64 we observed an increased rate of membrane endocytosis in sac9 mutants as compared to wild-type plants (Figure 4). Movement of internal vesicles is also increased in sac9-1 mutants as compared to wild-types. Columbia and sac9-1 stained with FM4-64

Figure 4. Fluorescence micrographs of wild-type Columbia strain of Arabidopsis thaliana (left) and the sac9-1 mutant (right) stained with the lipid-binding dye FM4-64.

 
MOVIES of vesicle movement in the root hairs of Arabidopsis thaliana Col-0 and sac9 mutant. Notice that the rate of movement of vesicles is much higher in the sac9 mutant. For ease of comparison, we have circled a single vesicle for the first half of each movie.
 
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