Lateral Roots with Different Initiation Paths
Primary, lateral and adventitious roots constitute the root system in seed plants. The primary root is formed at the embryo stage, while lateral and adventitious roots are mainly initiated post-embryonically. The textbooks of plant biology tell us that lateral roots derive from an existing root and adventitious roots are formed from non-root organs. However, how the root system is modified in response to diverse exogenous and endogenous cues is poorly understood.
It is widely accepted that the initiation of all lateral roots is dependent on an identical morphological and molecular path. Now, Dr. XU Lin and his colleagues at CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, overturn this traditional view by showing that although all the lateral roots look the same in their morphology, the molecular path underlying their initiation is different. A number of “lateral roots” deploy the adventitious rooting pathway for their initiation.
Using the model plant, Arabidopsis thaliana, XU and his colleagues find that, during adventitious rooting, WOX11, which encodes a transcription regulator, is activated by auxin (a plant hormone). WOX11 in turn activates LBD16 expression for adventitious root primordium initiation. However, when plants are vertically grown on medium, the lateral root is initiated by another pair of auxin-responsible transcriptional regulators, named ARF7 and ARF19, and this process does not require WOX11. ARF7 and 19 induces lateral production by activating LBD16. Therefore, WOX11-mediated adventitious rooting and non-WOX11-mediated lateral rooting converges to LBD16 activation to initiate root primordium.
To our surprise, XU and his colleagues further demonstrate that when plants are grown in soil or upon wounding, the primary root is able to produce both WOX11-mediated and non-WOX11-mediated roots. The non-WOX11-mediated lateral rooting pathway is mainly in response to the developmental cues, while the WOX11-mediated rooting pathway may contribute to the “lateral root” formation in response to environmental cues. These results suggest that the root system formation is highly flexible and the lateral roots are initiated with different molecular paths in response to developmental and environmental cues.
The study, entitled “Non-canonical WOX11-mediated root branching contributes to plasticity in Arabidopsis root system architecture”, was published in Development on Aug 29, 2017. This work is funded by National Natural Science Foundation of China, Ministry of Science and Technology of China, and Chinese Academy of Sciences.
Article website: http://dev.biologists.org/content/144/17/3126
WOX11-mediated and non-WOX11-mediated rooting pathways in root system formation
Lin Xu, Ph.D., Professor
National Key Laboratory of Plant Molecular Genetics
CAS Center for Excellence in Molecular Plant Sciences
Institute of Plant Physiology and Ecology
Chinese Academy of Sciences
Shanghai 200032, China