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Lateral root (LR) formation and development play a vital role in plant development by permitting the establishment of branched root systems. It is well known that nutrient availability controls LR development. Moreover, LR development is fine-tuned by a myriad of hormonal signals. Many transcription factors (TFs) participate in LR development. Here, we discuss the TFs involved in the nitrate and auxin signaling pathways and how these function in the regulation of LR formation and development in chrysanthemum. AtTCP20 is a plant-specific TF, which can modulate LR development in response to nitrate. The roles of CmTCP20 in LR development were identified by overexpression in chrysanthemum and heterologous expression in Arabidopsis. Overexpression of CmTCP20 significantly increased the number and average length of LRs compared with the wild type in chrysanthemum and Arabidopsis. We also found that CmTCP20 positively influenced auxin accumulation in the LRs at least partly by improving auxin biosynthesis, transport and response, thereby promoting LR development. Moreover, we found that CmTCP20 interacts with an auxin response factor, CmARF8, which also can be induced by nitrate and combined to proximal sites in the upstream promoter region of CmCYCB1;1 to positively regulate the cell cycle. The CmTCP20-CmARF8 heterodimer links nitrate and auxin signaling and converts cell-cycle signals to regulate LR initiation and growth. [ABSTRACT FROM AUTHOR]

Root system architecture is an important agronomic trait by which plants both acquire water and nutrients from the soil and adapt to survive in a complex environment. The adaptation of plant root systems to environmental constraints largely depends on the growth and development of lateral roots (LRs). MADS-box transcription factors (TFs) are important known regulators of plant growth, development, and response to environmental stimuli. However, the potential mechanisms by which they regulate LRs development remain poorly understood. Here, we identified a MADS-box chrysanthemum gene CmANR1 , homologous to the Arabidopsis gene AtANR1 , which plays a key role in the regulation of LR development. qRT-PCR assays indicated that CmANR1 was primarily expressed in chrysanthemum roots and was rapidly induced by exposure to high nitrate concentrations. Ectopic expression of CmANR1 in Arabidopsis significantly increased the number and length of emerged LRs compared to the wild-type (col) control, but had no obvious affect on primary root (PR) development. We also found that CmANR1 positively influenced auxin accumulation in LRs at least partly by improving auxin biosynthesis and transport, thereby promoting LR development. Furthermore, we found that ANR1 formed homo- and heterodimers through interactions with itself and AGL21 at its C-terminal domain. Overall, our findings provide considerable new information about the mechanisms by which the chrysanthemum MADS-box TF CmANR1 mediates LR development by directly altering auxin accumulation. [ABSTRACT FROM AUTHOR]