The SAUR gene family: the plant's toolbox for adaptation of growth and development.
Stortenbeker Niek,Bemer Marian
Journal of experimental botany
The family of small auxin up-regulated RNA (SAUR) genes is a family of auxin-responsive genes with ~60-140 members in most higher plant species. Despite the early discovery of their auxin responsiveness, their function and mode of action remained unknown for a long time. In recent years, the importance of SAUR genes in the regulation of dynamic and adaptive growth, and the molecular mechanisms by which SAUR proteins act are increasingly well understood. SAURs play a central role in auxin-induced acid growth, but can also act independently of auxin, tissue specifically regulated by various other hormone pathways and transcription factors. In this review, we summarize recent advances in the characterization of the SAUR genes in Arabidopsis and other plant species. We particularly elaborate on their capacity to fine-tune growth in response to internal and external signals, and discuss the breakthroughs in understanding the mode of action of SAURs in relation to their complex regulation.
The SAUR19 subfamily of SMALL AUXIN UP RNA genes promote cell expansion.
Spartz Angela K,Lee Sang H,Wenger Jonathan P,Gonzalez Nathalie,Itoh Hironori,Inzé Dirk,Peer Wendy A,Murphy Angus S,Overvoorde Paul J,Gray William M
The Plant journal : for cell and molecular biology
The plant hormone auxin controls numerous aspects of plant growth and development by regulating the expression of hundreds of genes. SMALL AUXIN UP RNA (SAUR) genes comprise the largest family of auxin-responsive genes, but their function is unknown. Although prior studies have correlated the expression of some SAUR genes with auxin-mediated cell expansion, genetic evidence implicating SAURs in cell expansion has not been reported. The Arabidopsis SAUR19, SAUR20, SAUR21, SAUR22, SAUR23, and SAUR24 (SAUR19-24) genes encode a subgroup of closely related SAUR proteins. We demonstrate that these SAUR proteins are highly unstable in Arabidopsis. However, the addition of an N-terminal GFP or epitope tag dramatically increases the stability of SAUR proteins. Expression of these stabilized SAUR fusion proteins in Arabidopsis confers numerous auxin-related phenotypes indicative of increased and/or unregulated cell expansion, including increased hypocotyl and leaf size, defective apical hook maintenance, and altered tropic responses. Furthermore, seedlings expressing an artificial microRNA targeting multiple members of the SAUR19-24 subfamily exhibit short hypocotyls and reduced leaf size. Together, these findings demonstrate that SAUR19-24 function as positive effectors of cell expansion. This regulation may be achieved through the modulation of auxin transport, as SAUR gain-of-function and loss-of-function seedlings exhibit increased and reduced basipetal indole-3-acetic acid transport, respectively. Consistent with this possibility, SAUR19-24 proteins predominantly localize to the plasma membrane.