PeFUS3 Drives Lateral Root Growth Via Auxin and ABA Signalling Under Drought Stress in Populus.

ABSTRACT Changes in root system architecture are vital for plant adaptation to drought stress, yet the underlying molecular mechanisms of this process remain largely elusive. Here, <italic>FUSCA3</italic> (<italic>FUS3</italic>), a B3 domain transcription factor isolated from <italic>Populus euphratica,</italic> was found to be an important gene of regulating lateral root (LR) development under drought stress. The expression of <italic>PeFUS3</italic> was strongly induced by ABA and dehydration treatments. Overexpressing <italic>PeFUS3</italic> in poplar 84 K (<italic>P. alba</italic> × <italic>P. glandulosa</italic>) positively regulated LR growth and enhanced drought tolerance, while the knockout lines, generated by the CRISPR/Cas9 system, displayed repressed LR growth and weakened drought tolerance. Further investigation demonstrated that <italic>PeFUS3</italic> activated the expression of <italic>PIN2</italic>, <italic>PIN6a</italic> and <italic>AUX1</italic>, which were key genes involved in auxin transport, suggesting <italic>PeFUS3</italic> modulated LR development under drought stress through auxin signalling. Moreover, <italic>PeFUS3</italic> directly upregulated <italic>PePYL3</italic> expression, and overexpressing <italic>PePYL3</italic> poplar lines exhibited significantly increased drought resistance. In addition, <italic>PeABF2,</italic> an ABA responsive transcription factor, interacted with <italic>PeFUS3</italic> and activated its transcription, indicating <italic>PeFUS3</italic> was involved in ABA signalling pathway. Taken together, <italic>PeFUS3</italic> is a key regulator, maintaining root growth of poplar by modulating the crosstalk of auxin and ABA signalling under drought stress. [ABSTRACT FROM AUTHOR]