Three Auxin Response Factors Promote Hypocotyl Elongation

Abstract

Plant organs grow to their final size by cell expansion. Several plant hormones, including auxin, brassinosteroids, ethylene, and GAs, regulate expansion growth, and environmental signals such as temperature and light can affect abundance of or responsiveness to these hormones (Wolters and Jürgens, 2009; Depuydt and Hardtke, 2011; Leivar and Monte, 2014). Integration of these signals with metabolic signals determines the degree of cell expansion and, hence, the final size of stems, leaves, and other organs. Hypocotyl elongation after seed germination is sensitive to multiple hormonal and environmental signals, and occurs largely by the expansion of cells produced in the embryo. In Arabidopsis (Arabidopsis thaliana), mutations in genes regulating light perception, hormone response, the circadian rhythm, or transcription can each affect hypocotyl elongation. Many such mutations also affect growth in other organs, indicating that common mechanisms regulate expansion growth in multiple tissues. Thus, the hypocotyl is a useful model tissue in which to explore general control mechanisms of cell expansion. High temperature and far-red-enriched light stimulate hypocotyl elongation, and the circadian rhythm gates hypocotyl elongation, in part by regulating auxin response. Integrated signals from these and other inputs affect the levels and activity of PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors (

miR167 limits anther growth to potentiate anther dehiscence

“…In addition, we included samples from stamens of P RPS5a >MIR167a plants overexpressing MIR167a. These plants resemble arf6 arf8 double mutant plants (Reed et al, 2018), and reveal effects of loss of the redundantly acting ARF6 and ARF8.…”

“…ARF6 and ARF8 similarly promote cell expansion in hypocotyls, inflorescence stems, petals, stamen filaments and stigma (Nagpal et al, 2005;Ru et al, 2006;Reeves et al, 2012;Reed et al, 2018), and many of the differentially expressed genes in arf6 arf8 and mARF8 stamens are also affected by arf6 mutations in seedlings or are auxin regulated in hypocotyls (Chapman et al, 2012;Oh et al, 2014). Despite this overlap, whereas SAUR (small auxin up RNA) genes are the dominant class of genes induced in hypocotyls by auxin or by light conditions that increase auxin production (Chapman et al, 2012;Kohnen et al, 2016;Sun et al, 2016), only one SAUR gene (SAUR42/At2g28085) was underexpressed in arf6 arf8 stamens and overexpressed in mARF8 stamens; and GO and protein domain analyses did not highlight SAUR genes in our dataset.…”

Progress of Research on the Regulatory Pathway of the Plant Shade-Avoidance Syndrome

“…In hypocotyls, the high level of PIF4 may induce transcripts of the early auxin-responsive genes MSG2/IAA19 and IAA29, which in turn reduce the expression level of the growth-repressive gene IAA17 (Hornitschek et al, 2012;Pucciariello et al, 2018). Recent studies demonstrate that three auxin-responsive factors (ARF6, ARF7, and ARF8) are conducive to hypocotyl elongation in low R:FR environments (Reed et al, 2018). With regard to PHYBmediated shade-avoidance responses, auxin contents and auxin-related genes are up-regulated to promote growth (Keuskamp et al, 2010), but hypocotyl elongation triggered by LBL does not involve alteration in detectable auxin amounts or sensitivity (Pedmale et al, 2016).…”

Genome-Wide Identification and Expression Analysis of Auxin Response Factor (ARF) Gene Family in Longan (Dimocarpus longan L.)

“…Although biochemical and genetic analyses have established a crucial function for ARF genes in plant growth and development, current knowledge of the biological roles of individual ARFs is mainly from the characterization of model plants Arabidopsis, rice and tomato. In Arabidopsis, ARF2 regulates leaf senescence and floral organ abscission independently of the ethylene and cytokinin response pathways [20]; ARF6, NPH4/ARF7, and ARF8 affect leaf and inflorescence growth, promoting hypocotyl elongation [21,22]. In rice, negative regulation of OsARF18 expression by OsmiR160 is critical for rice normal growth and development [23]; OsARF12 is regarded as one of major player in phosphate-induced auxin responses, indicating that ARFs might be involved in phosphate homeostasis in crops [24].…”