Isolation and identification of two new alleles of STICHEL in Arabidopsis

Plant trichome has long been selected as a model system to study the regulatory mechanism during cell development due to its unique growth characteristics. In an effort to explore new components that contribute to trichome development, we performed large-scale forward genetic screening in Arabidopsis, and found two recessive mutants with significant trichome branching defects, both of which display one branched trichomes. After map-based cloning, genetic complementation experiments, we confirmed that they are new alleles of STICHEL (STI) that has been reported to act as a key regulator of trichome branching. The predicted product of STI gene is comprised by three functional domains including a large domain with sequence similarity to eubacterial DNA polymerase III γ-subunit in the middle, two PEST domains in the N terminal, and two nuclear localization signals (NLS) at the very N terminal and C terminal, respectively. Our biochemistry and molecular analysis indicated that a PEST domain in the N-terminal could be important for STI functioning in regulating trichome branching. It can directly interact with BRACHLESS TRICHOME (BLT), an important linker of cell shape and endoreplication. Because the previously data showed that the function of STI in regulating trichome branching was not linked to DNA replication and actin or microtubule cytoskeleton configuration, our findings of the direct interaction domains between STI and BLT veiled the probable roles of STI in cell morphogenesis.