Abstract
BackgroundThe close planting of dwarfing self-rooted rootstocks is currently a widely used method for apple production; however, self-rooted rootstocks are weak with shallow roots and poor grounding. Therefore, understanding the molecular mechanisms that establish the gravitropic set-point angles (GSAs) of the adventitious roots of self-rooted apple stocks is important for developing self-rooted apple rootstock cultivars with deep roots.ResultsWe report that the apple FOUR LIPS (MdFLP), an R2R3-MYB transcription factor (TF), functions in establishing the GSA of the adventitious roots of self-rooted apple stocks in response to gravity. Biochemical analyses demonstrate that MdFLP directly binds to the promoters of two auxin efflux carriers, MdPIN3 and MdPIN10, that are involved in auxin transport, activates their transcriptional expression, and thereby promotes the development of adventitious roots in self-rooted apple stocks. Additionally, the apple auxin response factor MdARF19 influences the expression of those auxin efflux carriers and the establishment of the GSA of adventitious roots of apple in response to gravity by directly activating the expression of MdFLP.ConclusionOur findings provide new insights into the transcriptional regulation of MdFLP by the auxin response factor MdARF19 in the regulation of the GSA of adventitious roots of self-rooted apple stocks in response to gravity.
Highlights
The close planting of dwarfing self-rooted rootstocks is currently a widely used method for apple production; self-rooted rootstocks are weak with shallow roots and poor grounding
The results suggested that the endogenous hormone auxin and MdPINs may play an important role in the gravitropic set-point angle (GSA) of adventitious roots of self-rooted apple stocks
The apple auxin response factor MdARF19 influences the expression of those auxin efflux carriers and the establishment of the GSA of adventitious roots of apple in response to gravity by direct activation of its expression of MdFLP
Summary
The close planting of dwarfing self-rooted rootstocks is currently a widely used method for apple production; self-rooted rootstocks are weak with shallow roots and poor grounding. The plant hormone auxin, which integrates many endogenous and environmental signals regulating lateral root formation [17], commonly plays a key role in embryogenesis, organogenesis, morphogenesis, and cell determination and division [33, 48]. Terrestrial plants have evolved under gravitational forces and have the ability to use it as the most reliable signal for regulating their growth and morphogenesis [11, 36]. The orientation of plant growth relative to the gravity vector can be determined by the gravitropic set-point angle (GSA) [7]. Auxin controls the GSA in the lateral branches of higher plants; In addition, auxin regulates the GSA by adjusting the magnitude of antigravitropic offset component during the whole development process via TIR1/AFB-Aux/IAA-ARFdependent auxin signaling within the gravity-sensing cells of the roots and shoots [29]
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