Functional Analyses Of Two Transcription Factors, TCP15and TCP22, From Arabidopsis Thaliana

TCP15and TCP22are two highly homogeneous members of TCP family in Arabidopsis thaliana. Overexpression of a dominant negative version of TCP15, TCP15-SRDX, resulted in an upward curly rosette leaf phenotype. Overexpression of TCP15, on the other hand, resulted in a downward curly leaf phenotype, which is more evident for the3-week-old plants. These results suggest that TCP15plays an important role in leaf growth and development of Arabidopsis. Futher analysis indicated that the function of TCP15may through regulating the expression of IAMTl, which controls Arabidopsis leaf growth and development. The expression of IAMT1is altered in35S:TCP15-SRDX transgenetic plants compared to wild type plants. TCP15is localized in the nucleus because the fluorescence of the35S.TCP15-GFP transformed protoplasts is mainly observed in the nuleus. a T-DNA insertional mutant tcpl5shows no obvious differences with wild type plants, which is likely caused by functional redundant of TCP family members.Overexpression of a TCP22-SRDXfusion sequence in Arabidopsis drived either by a35S or a TCP22native promoter leads to a severe premature leaf senescence phenotype. We find that the leaves of35S.TCP22-SRDX and TCP22.TCP22-SRDX-GFP both displayed a lot of peroxide accumulation.35S:TCP22-GFP plants showed delayed leaf growth and development, indicating that TCP22negatively regulates leaf senescence.35S.TCP22-SRDX and TCP22:TCP22-SRDX-GFP also showed premature leaf senescence when seedings are grown on1/2MS medium, but the phenotype was much weaker than the ones grown in soil. Our promoter::GUS analysis indicated that TCP22is expressed more in older leaves than in younger leaves. We also find that TCP22is mainly localized in the nuleus based on the fluorescence analysis of the roots of the35S.TCP22-GFP transgenetic plants. The function of TCP22may be related to light, as the expression of TCP22is induced by light.35S:TCP22-SRDX, TCP22:TCP22-SRDX-GFP and35S:TCP22-GFP shows a similar phenotype with Col-0when grown in the dark. In the light35S:TCP22-SRDX plants showed more peroxide accumulation especially at leaf edges where more pigments accumulate. Trypan blue staining results also showed the similar results. A loss-of-function T-DNA insertion mutant, tcp22, showed no obviously defective phenotype compared to Col-0, which may be caused by functional redundancy of TCP family members. Because both35S:TCP15-SRDX and35S.TCP22-SRDX transgenetic plants showed premature leaf senescence phenotypes, it suggests that TCP15and TCP22may play a redundant role in regulating leaf scenescence.