Characterization of CRISPR-Cas9 Induced SAUR19 Family Mutants in Arabidopsis.

Abstract

The plant hormone auxin (IAA) regulates many aspects of plant growth and development. Small auxin up RNA (SAUR) genes are highly transcribed in response to auxin, whose differential transport and accumulation creates gradients that regulate various aspects of plant development such as: tropisms, root initiation, and cellular division and differentiation. Previous studies using overexpression of GFP-tagged SAUR proteins have shown that SAURs may function as positive regulators of cellular expansion. To provide additional evidence for this hypothesis, I investigated the effect of creating knockouts of multiple members of the SAUR19 subfamily using CRISPR/Cas9. Additionally, SAUR-promoter-GUS staining was performed to identify the location of SAUR 13, 22, 27, 28, and 29 expression. These studies revealed strong SAUR expression in adult leaf vasculature, expanding stamen filaments, hypocotyls, and petioles. Through analysis of heat-induced growth, we show that knockout of SAURs 19, 20, 21, 22, 24, and 29 conferred a modest decrease in both hypocotyl and petiole length. While not severe, this difference provides supportive evidence that SAURs function as positive regulators of cell expansion, and it also reinforces the hypothesis that SAURs have extensive genetic redundancy. Higher numbers of SAUR knockouts should produce stronger phenotypes and provide definitive evidence of SAUR function.