The plant hormone auxin modulates cell proliferation and cell expansion in part by changing gene expression. Among the three primary auxin response gene families, Aux/IAA, GH3 and SAUR, the function of SAUR genes remains unclear. SAUR transcripts were initially identified in epidermal and cortical cells of elongating tissues and thus were supposed to regulate cell expansion downstream of auxin transport and auxin signaling. Recent studies have proposed that SAUR proteins are able to modulate auxin transport and cell expansion by an unknown mechanism. We present our work on the SAUR41 subfamily genes of Arabidopsis (SAUR41, SAUR40, SAUR71 and SAUR72). Similar to the fusion protein between SAUR41 and EGFP, both SAUR40-EGFP and SAUR71-EGFP were identified in the cytoplasm of all types of root tip cells. This result indicated that the subcellular location pattern of SAUR proteins among the members of the same subfamily could be similar to each other, although the overall location pattern of SAUR proteins appeared to be highly diverse. SAUR41 was distinctively expressed in the quiescent center and cortex/endodermis initials of root stem cell niches and in the endodermis of hypocotyls, whereas SAUR71 and SAUR72 were expressed in the steles of young roots and hypocotyls. In addition, SAUR71 was differentially expressed during stomatal formation. The tissue-specific and developmentally regulated expression patterns of the SAUR41 subfamily genes imply that SAUR transcripts or SAUR proteins might serve as signal molecules to ensure the coordination of cell proliferation and cell expansion. Finally, Arabidopsis seedlings expressing TAP (tandem affinity peptide) tagged SAUR41 displayed phenotypes, indicating that it was rational to use the TAP approach for identification of potential binding partners of SAUR41 proteins.
Keywords: Arabidopsis; SAUR; auxin transport; cell expansion; root meristem patterning; stomatal development.