Molecular Mechanism Of OsARF19Controlling Leaf Angle In Rice (Orvza Sativa)

Leaf angle (lamina inclination or lamina joint bending) is the degree of bending between the leaf blade and leaf sheath or the inclination between leaf blade and culm. Leaf angle is an important agronomic trait for determining plant architecture and grain yield. According to published reports, auxin and brassinosteroid (BR) are involved in controlling lamina inclination, while the molecular mechanism of auxin and BR signaling crosstalk for regulating lamina inclination is still not well understood. It has been reported that auxin response factors (ARFs) participate in controlling various aspects of growth and development in dicot, such as Arabidopsis. However, the biological functions of ARF are still unclear in monocot rice plant. In this study, we focused on the regulatory mechanism of rice leaf angle, and we investigated the roles of OsARF19in regulating leaf angle size and explored the network of OsARF19-mediated auxin and BR signaling by using OsARF19overexpression lines as materials. These results are summarized as following:(1) In OsARF19overexpression lines, the plant architecture is altered. Compared with WT/NIP, OsARF19overexpression lines show dwarfism, narrow leafs, low setting rates and thin seeds, especially, increased leaf angle. The measurement of collar lengths and the observation of resin sections indicated that the enlarged lamina inclination due to increase of its adaxial cell division.(2) OsARF19is involved in the regulatory mechanism of controlling rice leaf angle mediated by auxin. OsARF19is a transcription factor in auxin signal transduction. The expression of genes (OsIAA1, OsARF23and OsTIR1) related to leaf inclination and involved in auxin signaling were altered in OsARF19overexpression lines. In addition, the expression of OsARF19in osafb2or its upstream OsmiRNA393overexpression lines was also up-regulated.(3) OsARF19is constitutively expressed in rice tissues and organs, especially highly expressed in shoot and lamina joint. Furthermore, its expression is strongly induced by auxin and BR.(4) OsGH3-5acts as target of OsARF19. Chromatin immunoprecipitation (ChIP) and yeast one-hybridization assays demonstrated that OsARF19binds to the promoter of OsGH3-5directing its expression. Furthermore, OsGH3-5overexpression lines showed a similar phenotype to OsARF19overexpression lines. However, osarf19-T-DNA and osgh3-5-Tos17mutants without erected leaves show a function redundancy with other members of their gene family.(5) The subcellular localization of OsGH3-5is demonstrated to be in the nucleus, cytoplasm and the ER using transient expression of OsGH3-5fused to a green fluorescent protein (GFP) in tobacco and rice protoplasts. ER is thought to be an important compartment for conjugating excess IAA to various amino acids.(6) OsARF19is involved in the regulatory mechanism of rice leaf angle mediated by BR. OsARF19overexpresion lines are sensitive to exogenous BR treatment and altered the expressions of genes related to BR response and BR biosynthesis. Moreover, OsARF19could bind to the OsBRI1promoter and up-regulate the expression of OsBRI1, suggesting that OsARF19might be a positive regulator involved in BR signaling.In conclusion,OsARF19as a transcription factor in auxin signaling, participates in the regulatory mechanism of controlling rice leaf angle, and links auxin and BR signaling. These findings provide novel insights into auxin and BR signaling, this might have significant implications for improving plant architecture of monocot crops and lay foundation for agricultural production of reasonably dense planting of rice.