Auxin is a plant hormone that regulates cell division, differentiation, and elongation during growth and development. The SAUR (SMALL AUXIN UP RNA) family of genes is one of three families of auxin-response genes, and is relatively understudied compared to the other two. A subfamily of SAUR genes called SAUR41 contains four different individual genes and has been found through data mining to be induced by the hormone abscisic acid (ABA), though its exact function is unknown.
In a recent study published in Annals of Botany, Ting Qiu and colleagues used the gene-editing system CRISPR/Cas9 to produce mutants both without SAUR41 expression (that is, a quadruple mutant) and with the genes over-expressed, with the goal of determining their function. The researchers investigated the mutants and wild type via structural analysis, analysis of the transcriptome, and characterization of the plants’ physiology.
The group found that mutants with no SAUR41 function had less expansion and elongation of the cells of the hypocotyl (seedling stem) and cotyledons, while overexpression caused increased expansion and elongation. Both overexpression and no expression caused irregular cell size and shape in certain cells of the hypocotyl. Both mutant types also became hypersensitive to salt stress at the point of seedling establishment, indicating a role for the genes in salt tolerance. Finally, knocking out SAUR41 subfamily gene function led to increased activity related to calcium homeostasis genes, while overexpression decreased the activity of genes related to iron homeostasis. Taken together, these results point to a role for the SAUR41 genes in ion homeostasis.
Though the exact mechanisms of action of SAUR41 genes are largely unknown, the work represents an improvement in our understanding of the genetic basis of seedling establishment and salt tolerance. “Further investigation is needed to elucidate how the SAUR41 pathway interacts with the core ABA signalling pathways,” the authors write. “In addition, further examination of cell size in single, double and triple mutants would help to reveal distinctive and/ or overlapping roles of individual members of SAUR41 genes for cell size control. Considering that SAUR41 genes are ABA inducible and ABA is a key hormone in plant abiotic stress signalling, our work may provide new candidate genes for improvement of plant abiotic stress tolerance.”