The SAUR41 subfamily of cell expansion-promoting genes modulates abscisic acid sensitivity and root touch response: a possible connection to ion homeostasis regulation.

Most primary auxin response genes are classified into three families, namely AUX/IAAs, GH3s, and SAURs. As a rapidly developing field of plant biology, recent studies have begun to address the function and mechanism of plant SAURs. We found that, in Arabidopsis, the SAUR41 subfamily genes were ABA-inducible, and overexpression of SAUR41 induced the biosynthesis of ABA. The saur41/40/71/72 quadruple mutants and the SAUR41 overexpression lines had an altered expression of ABA and calcium homeostasis/signaling genes, but not the AUX/IAAs and GH3s. Here, we reported that the quadruple mutants showed an increased sensitivity to ABA treatment, in terms of cotyledon greening/expansion rate, while for the overexpression lines, this was decreased. With respect to the root touch response, the overexpression of SAUR41 led to an extensive root looping phenotype, while the quadruple mutations of saur41s led to a relaxed root looping. As reported, the ion content (Na+, K+ and Fe2+), apoplast acidification ability, and salt tolerance were also abnormal in the quadruple mutants and/or the SAUR41 overexpression lines. Our work supports an emerging concept that ABA and calcium are integrated together to modulate ion homeostasis. In addition, our work demonstrates that SAUR41s might be new components for the regulation of ion homeostasis by ABA and calcium.