Aux
''Aux'' is an abbreviation with multiple meanings. For its uses in science and technology, including biology, computing, and electronics, see the "Science and technology" section. For other uses in business and organizations, media, and transportation, see the "Other uses" section.Science and technology
Biology
In plant biology, Aux/IAA and Aux/LAX commonly refer to components of the auxin signaling pathway, a key regulatory system involving the hormone indole-3-acetic acid (IAA) that governs growth, development, and environmental responses.[1] Auxin-responsive genes, particularly those abbreviated as Aux/IAA and Aux/LAX, encode proteins critical for perceiving and translocating this hormone within cells and tissues.[2] The Aux/IAA gene family was first identified in the early 1980s through studies on auxin-responsive transcripts in peas and soybeans,[3] with comprehensive characterization in Arabidopsis thaliana emerging in the late 1990s via genetic screens for mutants exhibiting altered auxin sensitivity.[4] Key experiments, such as those isolating dominant mutations in genes like AXR2/IAA7 and AXR3/IAA17, revealed that Aux/IAA proteins are short-lived transcriptional repressors that accumulate in the absence of auxin to inhibit growth-related gene expression.[5] In 2001, researchers demonstrated that Aux/IAA degradation is mediated by the SCF^{TIR1} ubiquitin ligase complex, where auxin binding to TIR1/AFB receptors promotes Aux/IAA ubiquitination and subsequent proteasomal breakdown, thereby derepressing auxin response factors (ARFs) to activate downstream targets.[6] Aux/IAA proteins, numbering 29 in Arabidopsis, function as repressors by forming heterodimers with ARFs via their domain II motif, preventing ARF binding to promoters of genes involved in cell division, elongation, and differentiation.[1] This repression is relieved upon auxin-induced degradation, enabling precise spatiotemporal control of processes like apical-basal patterning in embryos and vascular differentiation.[7] For instance, mutations in specific Aux/IAA genes, such as IAA12/BDL, disrupt embryogenesis by stabilizing the repressor and blocking ARF5/MP activity, highlighting their role in hormone-mediated developmental checkpoints.[8] The Aux/LAX gene family encodes auxin influx carriers that facilitate IAA uptake into plant cells, complementing efflux carriers like PIN proteins to establish polar auxin gradients essential for organ formation.[9] In Arabidopsis, the four members—AUX1, LAX1, LAX2, and LAX3—share a conserved structure with 11 transmembrane helices forming a central pore, as resolved in recent cryo-EM studies of AUX1, which binds IAA via a tyrosine-lined binding pocket to drive proton-coupled transport.[10] AUX1 predominates in root gravitropism and lateral root initiation, where it localizes to protophloem cells to redistribute auxin toward pericycle founder cells, promoting asymmetric growth.[11] LAX proteins, particularly LAX3, play specialized roles in embryogenesis and lateral root development by enabling auxin maxima at susceptible sites, such as during procambial cell specification in the embryo axis.[12] Genetic evidence from aux1 lax mutants shows defective embryo patterning and reduced root branching, underscoring their non-redundant functions in auxin homeostasis despite sequence similarities.[13] While auxin biosynthesis primarily occurs via the indole-3-pyruvic acid pathway in young tissues, Aux/LAX carriers ensure efficient distribution of the synthesized hormone to responsive cells.[14]Computing
In MS-DOS and early operating systems, the AUX designation refers to a reserved filename and device driver for the auxiliary serial port, typically mapped to COM1 or COM2 for communication with peripherals like modems and printers. Introduced with MS-DOS 1.0 in 1981, this device enabled basic serial I/O operations, allowing users to redirect output directly to external hardware. For instance, the commandTYPE file.txt > AUX would transmit the contents of a file to the connected serial device, supporting early networking and printing tasks without dedicated software.[15][16]
In Unix-like systems, auxiliary input/output operations, often tied to serial ports for debugging and low-level communication, are managed through device files in the /dev directory, such as /dev/ttyS0 for the primary serial interface. Programmers access these for raw I/O via system calls like open() and read(), enabling direct interaction with hardware in applications requiring precise control, such as embedded systems or terminal emulators. This approach treats devices as files, aligning with Unix's "everything is a file" philosophy and facilitating portable code for auxiliary tasks.[17][18]
Auxiliary storage concepts in computing trace back to early systems where "aux" denoted secondary memory supplementing primary storage, such as RAM acting as auxiliary to CPU registers for temporary data holding. Historically, this evolved from magnetic drums and tapes in the 1950s to disks in the 1960s, providing non-volatile, high-capacity alternatives to volatile main memory for archiving and program loading. In assembly languages, "aux" terminology appears in contexts like the auxiliary carry flag (AF) in x86 instruction sets, used for detecting carries in BCD arithmetic operations since the 1970s Intel processors. Modern caching mechanisms build on these foundations but retain the legacy focus on hierarchical memory access.[19][20]