Changes in auxin distribution patterns during lateral root development in rice

Root differentiation in plants is mediated by the hormone auxin. As auxin is implicated in coordinating the development and organization of tissues in lateral roots, we investigated the inferred cellular distribution of auxin in various cell types in root prior to and during lateral root formation in rice (Oryza sativa cv. Murasaki R86) using the transgenic plants carrying the auxin responsive soybean GH3 promoter fused to gusA. Modulation in the expression of the PrGH3:gusA fusion was assessed by histological GUS staining in rice tissues following the treatment of transgenic rice seedlings with or without auxins such as 2,4-dichlorophenoxyacetic acid (2,4-D) or N-naphthaleneacetic acid (NAA), and the auxin transport inhibitors N-(1-naphthyl)phthalamic acid (NPA), kaempferol, quercetin, apigenin or Nod factors under axenic conditions. In this work we demonstrate that soybean GH3 promoter is active in rice, and the GH3-gusA reporter system can be utilized as a molecular marker to monitor the changes in auxin levels during organogenesis of this monocot plant. Our studies revealed distinct patterns of GH3 activity prior to and during various developmental phases of lateral root differentiation in rice. The GH3 expression patterns during lateral root development in rice showed considerable similarities with those occurring during comparable stages of lateral root development in dicots, implying that the requirement of auxin for the morphogenesis of lateral roots is similar in evolutionarily distinct monocots and dicots.