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. 2021 May 24;22(11):5508. doi: 10.3390/ijms22115508

Figure 2.

Figure 2

Regulation of primary root (PR) growth by various hormones and their crosstalk. (A) Auxin effects root growth in a concentration-dependent manner and interacts with ET signalling pathway to control PR elongation. Low concentration of auxin promotes PR growth probably via free AUX/IAAs, while high concentration inhibited PR growth through TIR1-mediated signalling via an unknown non-transcriptional mechanism (B) CK signalling modulates PR growth via AUX-1 mediated auxin translocation. (C) BR induces ET production via stabilizing ACS5, and ACS9 represses ET synthesis through BES1 and BZR1-mediated repression of ACS7, ACS9, and ACS11 to control PR growth. (D) MYC2, a DNA binding bHLH transcription factor in JA signalling, represses the transcriptional expression of PLT1 and PLT2. JA regulates expression of ASA1 and modulates auxin levels to cause root growth inhibition. JA and auxinsignalling occurs via AXR1 to control PR growth. (E) SA via NPR1-mediated signalling establishes an auto regulatory feedback regulation between CK2 and SA to link between SA signalling and auxin transport. SA also led to inhibition of PR elongation in NPR1-independent manner via affecting PP2A, leading to changes in PIN activity and auxin export, resulting in attenuation of root growth. Solid black arrow indicates confirmed pathway. Blue arrow indicates low levels of auxin, green arrow indicates high levels of auxin. Red circle indicates phosphorylation.