The Auxin-induced Maize Gene ZmSAUR2 Encodes a Short-lived Nuclear Protein Expressed in Elongating Tissues

Abstract

By differential screening of a cDNA library from auxin-induced maize coleoptiles we have isolated and characterized a SAUR gene, designated ZmSAUR2, belonging to a not yet characterized subtype of the SAUR family. ZmSAUR2 encodes a 15.3-kDa protein and is specifically induced by auxin in elongating coleoptile tissue but not in primary leaves or in roots. The transcript level rapidly increased within minutes and preceded auxin-stimulated elongation of coleoptile segments. Cycloheximide also induced ZmSAUR2 transcription, as has been shown for other early auxin-induced genes, whereas abscisic acid, brassinolide, ethylene, gibberellic acid, kinetin, and methyl jasmonate did not provoke an increase in ZmSAUR2 mRNA abundance. In pulse-chase experiments using auxin-induced coleoptiles and an anti-Zm-SAUR2 antibody we were able to precipitate a protein of the expected molecular mass and to determine a half-life of about 7 min, which is among the shortest known in eukaryotes. In gel shift assays binding of calmodulin to ZmSAUR2 was demonstrated, suggesting the possibility of post-transcriptional regulation. Upon transformation of onion epidermal cells with a ZmSAUR2::GUS construct the corresponding chimeric protein was detected in the nucleus. The results suggest that ZmSAUR2 encodes a short-lived nuclear protein that might be involved in auxin-mediated cell elongation.

SAUR36, a SMALL AUXIN UP RNA Gene, Is Involved in the Promotion of Leaf Senescence in Arabidopsis

“…These data suggest that SAUR36 may inhibit cell enlargement. Early studies have also shown that some SAUR proteins play a role in auxin-modulated cell elongation (Hagen and Guilfoyle, 2002;Knauss et al, 2003;Hagen et al, 2010).…”

“…Like most SAUR genes in Arabidopsis (Knauss et al, 2003), the SAUR36 gene consists of only one exon (Fig. 3A) that encodes a protein with 162 amino acid residues.…”

“…Analysis of Arabidopsis plants expressing a SAUR15-luciferase fusion protein suggested that SAUR proteins are unstable (Zenser et al, 2003). Studies of the maize (Zea mays) ZmSAUR2 protein revealed that SAUR expression may be regulated at the protein level (Knauss et al, 2003). Recent studies showed that OsSAUR39 acts as a negative regulator of auxin synthesis and transport; overexpression of this gene in rice (Oryza sativa) confers phenotypes including reductions in lateral root development, yield, and shoot and root lengths (Kant et al, 2009).…”

Functional Genomic Analysis of theAUXIN RESPONSE FACTORGene Family Members inArabidopsis thaliana: Unique and Overlapping Functions ofARF7andARF19

“…Several GH3-like proteins covalently modify IAA, jasmonic acid, or salicylic acid, indicating that they play a global role in various hormone signaling pathways. The function of the SAUR-like genes is still unknown, but it has been suggested that they may encode short-lived nuclear proteins involved in auxin signaling by interacting with calmodulin (Yang and Poovaiah, 2000;Knauss et al, 2003).…”

Constitutive Expression of Arabidopsis SMALL AUXIN UP RNA19 (SAUR19) in Tomato Confers Auxin-Independent Hypocotyl Elongation

“…These proteins are unique to plants and contain no obvious motifs suggestive of a biochemical function. Several SAUR proteins are highly unstable and appear to be subject to ubiquitin-mediated proteolysis (Knauss et al, 2003;Chae et al, 2012;Spartz et al, 2012;Li et al, 2015). However, the addition of an epitope or GFP tag can dramatically stabilize SAUR proteins.…”