parg1-1 is a long circadian period mutant
The lack of effect of PARP and SRT mutants on circadian
period might be unexpected because the tej-1 mutation ofPARG1 , which is predicted to encode a poly(ADPribose)
glycohydrolase that counter acts PARP activity has been reported to
increase the period of circadian rhythms in Arabidopsis (Panda et
al ., 2002). We therefore reinvestigated whether lesions in PARG1can affect circadian period. As reported previously, tej-1 (a
point mutation which results in a change of the glycine at position 262
to a glutamic acid) increases circadian period (Supplemental Figure 5a,
C24 26.8 ± 0.6 h, tej -1 30.5 ± 2.64 h, P = 0.006). Having
confirmed the phenotype of the tej-1 mutant, we next sought to
confirm whether the phenotype of tej-1 was due to a lesion inPARG1. We obtained a second allele of PARG1(At2g31870), we named as parg1-1 (SALK_147805, NASC;
Figure 5a). When transformed with the CCA1::LUC reporter,parg1 -1 mutants had a slightly longer circadian period of
luminescence (Supplemental Figure 5b, Col-0 24.5 ± 0.6 h, parg1 -1
24.8 ± 0.4 h, P = 0.021). The mean period in circadian rhythms of leaf
movement was 1 - 1.5 hours longer than wild type (Figure 5b, Col-0 24.3
± 1.0 h, parg1-1 25.4 ± 1.3 h, P < 0.001). Similarly,
circadian rhythms in DF were long period in the parg1-1 mutant
(Figure 5c, Col-0 23.4 ± 0.9 h, parg1-1 25.0 ± 1.1 h, P = 0.011).
We also isolated insertion mutants of PARG2 (At2g31865),parg2-1 (GK072_B04, NASC), to determine if this close gene
family member might also contribute to circadian regulation (Figure 5a).
The parg2-1 mutant by contrast had weak to no effect on circadian
rhythms of leaf movement (Figure 5d, Col-0 24.5 ± 0.7 h, parg2-124.8 ± 0.6 h, P = 0.209) or delayed chlorophyll fluorescence (Figure 5e,
Col-0 24.23 ± 3.06 h, parg2 -1 23.2 ± 0.8 h, P = 0.667). Thus, the
effects of the PARG1 mutant are specific to that member of the
gene family.