OsIAA11-mediated Auxin Signaling Controls Lateral Root Initiation In Rice

Lateral roots are important for plants to uptake of nutrients and water. Several members of the Aux/IAA family play crucial roles in lateral root (LR) development in Arabidopsis,while the knowledge on LR development in crops is still limited. Here, we isolated a gene for a member of the rice Aux/IAA family, OsIAA11(LOC_Os03g43400), from a rice mutant defective in lateral root development. The stabilizing mutation of OsIAA11strictly blocks the initiation of lateral root primordia, but it does not affect crown root development and plant growth. The expression of OsIAAll is defined in root tips, lateral root caps, steles and lateral root primordia. Auxin signaling marked by the DR5-GUS reporter (B-glucuronidase) and GFP fluorescence indicates that OsIAA11mediates auxin signaling in root caps and lateral root caps. Transcript levels of OsPINlb,OsPIN5a, OsPIN9, OsPIN1Oa and OsAUXl, a homolog of AtAUX1in rice, were diminished in root tips of the Osiaall mutant. This result implies that OsIAA11mediates an acropetal-basipetal auxin signaling loop and consequently regulates lateral root initiation in rice. OsARF16is an ortholog of AtARF7/AtARF19, which are involved in lateral root initiation in Arabidopsis. Transgenic plants with point mutation at domain IV of several AUXIN RESPONSE FACTOR (ARF) belong to subclass IIa, including ARF6, ARF12, ARF16, ARF17, ARF19and ARF25, under the background of stabilizing of OsIAA11did not rescue lateral roots in Osiaall mutant. Double mutation of arf6;arf12, arf6;arfl6, arf6;arf17, arf16;arf25and arfl2;arf25, also did not show rescue of LR in Osiaall mutant., suggesting that the function of OsARFs might be diverse between rice and Arabidopsis. These results may also reflect the functional redundancy of ARFs under OsIAA11.Our findings indicate that OsIAA11is a key regulator of regulating an acropetal-basipetal auxin signaling loop.