Plant hormone auxin plays critical roles in controlling almost every aspect of plant growth and development, such as phototropic and gravitropic responses. It has fascinated plant biologists since its discovery in 1930s. One of the features about this small molecule is the polar auxin transport and polarity of its transporters. However, the mechanisms have not been well understood.  

Recently, scientist from the Institute of Botany of the Chinese Academy of Sciences (CAS), together with collaborators, identified new players in modulating polarity of auxin transporters.  

They found that three suppressor of actin (SAC) domain and transmembrane domain containing phosphoinositide phosphatases control the homeostasis of phosphoinositides, PtdIns4P and PtdIns(4,5)P2, in the model plant Arabidopsis thaliana.  

The double and triple mutants of the three SAC genes displayed severe developmental defects or lethality, with dramatic increase of PtdIns4P and PtdIns(4,5)P2 contents. The auxin peaks and polarity of auxin transporters were disrupted, likely due to the delay of recycling of the transporter proteins in the mutant plant cells.  

"These findings revealed new genes and related mechanisms modulating the polarity of auxin transporters, and the conserved functions of the SAC phosphoinositide phosphatases with transmembrane domain in eukaryotes," said Prof. CHENG Youfa, correspondence author of the study. 

This study has been published online in the journal New Phytologist.  

Wild type (WT) vs. sac mutant cells. PtdIns4P and PtdIns(4,5)P2 accumulation and disruption of auxin transporter protein cycling and polar localization in the SAC mutant cell. (Image by IBCAS)