Arabidopsis Inositol Polyphosphate 6-/3-Kinase (AtIpk2β) Is Involved in Axillary Shoot Branching via Auxin Signaling

The Arabidopsis (Arabidopsis thaliana) inositol polyphosphate 6-/3-kinase gene (AtIpk2β) is known to participate in inositol phosphate metabolism. However, little is known about its physiological functions in higher plants. Here, we report that AtIpk2β regulates Arabidopsis axillary shoot branching. By overexpressing AtIpk2β in the wild type and mutants, we found that overexpression of AtIpk2β leads to more axillary shoot branches. Further analysis of AtIpk2β overexpression lines showed that axillary meristem forms earlier and the bud outgrowth rate is also accelerated, resulting in more axillary shoot branches. The AtIpk2β promoter/β-glucuronidase (GUS) fusion (AtIpk2β∷GUS) expression pattern is similar to that of the auxin reporter DR5∷GUS. Moreover, AtIpk2β can be induced in response to exogenous indole-3-acetic acid (IAA) treatments. In addition, AtIpk2β overexpression plants exhibit IAA-related phenotypes and are more resistant to exogenous IAA treatments. Further analysis employing reverse transcription-polymerase chain reaction shows that some genes, including auxin-biosynthesis (CYP83B1), auxin-transport (PIN4), and auxin-mediated branching genes (MAX4 and SPS), are regulated by AtIpk2β. Taken together, our data provide insights into a role for AtIpk2β in axillary shoot branching through the auxin signaling pathway.