TIC Controls Root Meristem Size By Changes Of Auxin Accumulation In Arabidopsis

Auxin plays a centre role in regulating plant cell elongation and division, promoting cell specification, and acts upon many aspects of plant growth and development, including embryo patterning, vascular-differentiation, and maintenance of shoot and root meristem, apical dominance and tropic responses. Using physiological, biochemical and genetic methods, we demonstrate that TIC participates in controlling root meristem size by regulating auxin accumulation in Arabidopsis.1, The reduced root meristem size in tic-2is independent of the circadian clock.When compared with wild-type, tic-2has shorter meristem length and less meristem cells, which is independent on the photoperiods and diurnal time. We cross tic-2with CycB1;1::GUS, and detect their GUS activity. Our data further shows that mutant in TIC reduces the competence of meristematic cells to divide.2, TIC promoter is highly active in root meristem.By quantitative RT-PCR in different organs, we found that TIC was universally expressed in all tested organs with the highest level in flowers. GUS staining data of the transgenic lines with α β-glucuronidase (GUS) reporter under the control of TIC promoter shows that the TIC::GUS lines have a gradient staining with the strongest activity in the root meristem3, The decreased auxin accumulation is responsible for the reduced meristem size of tic-2root. The fluorescence intensity of DR5::GFP in the roots of tic-2was dramatically decreased compared with that of wild-type roots. The result of the measurement of endogenous IAA by GC-MS also demonstrates that IAA levels were significantly lower in tic-2than those in wild-type. Furthermore, we find that exogenous auxin can partially rescue the development defect present in root meristem of tic-2mutant.4, Acropetal auxin transport is reduced in tic-2We assayed auxin transport by applying3H-IAA to the root-shoot junction, and a significant decrease of auxin movement in tic-2was observed. Aerial parts detached experiment confirm that shoot-derived auxin participates in TIC-mediated root meristem development.5, PIN genes are down-regulated in tic-2We analyze the expression levels of four PIN genes by quantitative RT-PCR, and find that the transcript levels of these four PINs were dramatically repressed in tic-2compared with those in wild-type plants. PIN::PIN-GFP lines were crossed to tic-2for further confocal analysis, and the fluorescence intensities are remarkably reduced in tic-2.6, Mutation of TIC represses the expression of PLT familyUsing quantitative RT-PCR, we verify that PLT1/2, but not SCR/SHR are down-regulated by low auxin in tic-2mutant for reduced meristem size, which is further confirmed by analysis of PLT1::CFP in wild-type and tic-2seedlings.7, TIC regulates meristem size independent of MYC2The result that myc2-1tic-2has a reduced meristem comparable to tic-2, demonstrates that TIC regulates meristem size though auxin-PLTs loop independent of MYC2in the absent of JA. Conversely, myc2-1tic-2acts similar to myc2-1in the present of exogenous JA, indicating a complex regulation of root meristem by TIC/MYC2in different conditions (with/without JA).