| dc.description.abstract | The expression of genes that control iron (Fe) uptake and distribution (i.e., Fe utilization-
related genes) is under a strict regulation. Fe deficiency strongly induces Fe utilization-
related gene expression; however, little is known about the mechanisms that regulate this
response in plants. In this dissertation, a RNA metabolism factor, RNA POLYMERASE II
CTD-PHOSPHATASE-LIKE1 (CPL1) was shown to localize to the root stele, and to be
involved in the regulation of Fe deficiency responses in Arabidopsis thaliana. An analysis
of multiple cpl1 alleles established that cpl1 mutations enhanced transcriptional responses
of Fe utilization-related genes, e.g. IRON-REGULATED TRANSPORTER1 (IRT1), to low
Fe availability. In addition to the lower Fe content in the roots, but higher Fe content in
the shoots of cpl1-2 plants, the root growth of cpl1-2 showed improved tolerance to Fe
deficiency. Genetic data indicated that cpl1-2 likely activates Fe deficiency responses
upstream of both FE–DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT)-
dependent and -independent signaling pathways. Interestingly, various osmotic
stress/ABA-inducible genes were up-regulated in cpl1-2, and the expression of some
ABA-inducible genes was controlled by Fe availability.
Unlike Fe, accumulation of the heavy-metal cadmium (Cd) in plants is toxic and it is
absorbed by the roots due to the low selectivity of metal transporters such as AtIRT1. In
this dissertation, CPL1 was also shown to regulate the transcriptional responses to Cd
toxicity. cpl1-2 showed higher tolerance to the Cd toxicity by enhancing the root-to-shoot
translocation of Cd by an unknown mechanism. A knowledge-based screening resulted
in identification of a putative metal transporter, OLIGOPEPTIDE TRANSPORTER (OPT),
which was highly induced in cpl1-2 upon exposure to Cd. OPT was localized to the
plastids, indicating a role of plastids in Cd transport and accumulation. The root growth
of opt mutants showed higher tolerance to the Cd toxicity, and the mutants accumulated
less Cd, Fe and Zn, indicating the involvement of OPT in the transport of these metals.
This presented dissertation suggests that 1) CPL1 functions as a negative regulator of the
Fe deficiency signaling at the crosstalk with a branch of the osmotic stress/ABA signaling
pathway, and 2) CPL1 regulates the Cd distribution in plants by repressing the expression
of OPT. | en |
