| Summary: | Ultraviolet-B (UV-B) radiation is one of the important environmental factors limiting plant growth. Both abscisic acid (ABA) and microtubules have been previously reported to be involved in plant response to UV-B. However, whether there is a potential link between ABA and microtubules and the consequent signal transduction mechanism underlying plant response to UV-B radiation remains largely unclear. Here, by using <i>sad2-2</i> mutant plants (sensitive to ABA and drought) and exogenous application of ABA, we saw that ABA strengthens the adaptive response to UV-B stress in <i>Arabidopsis thaliana</i> (<i>A. thaliana</i>). The abnormal swelling root tips of ABA-deficient <i>aba3</i> mutants demonstrated that ABA deficiency aggravated the growth retardation imposed by UV-B radiation. In addition, the cortical microtubule arrays of the transition zones of the roots were examined in the <i>aba3</i> and <i>sad2-2</i> mutants with or without UV-B radiation. The observation revealed that UV-B remodels cortical microtubules, and high endogenous ABA can stabilize the microtubules and reduce their UV-B-induced reorganization. To further confirm the role of ABA on microtubule arrays, root growth and cortical microtubules were evaluated after exogenous ABA, taxol, and oryzalin feeding. The results suggested that ABA can promote root elongation by stabilizing the transverse cortical microtubules under UV-B stress conditions. We thus uncovered an important role of ABA, which bridges UV-B and plants’ adaptive response by remodeling the rearrangement of the cortical microtubules.
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