An official website of the United States government
Shade avoidance syndrome is an important adaptive strategy. Under shade, major transcriptional rearrangements underlie the reallocation of resources to elongate vegetative structures and redefine the plant architecture to compete for photosynthesis. BBX28 is a B-box transcription factor involved in seedling de-etiolation and flowering in Arabidopsis (Arabidopsis thaliana), but its function in shade-avoidance response is completely unknown. Here, we studied the function of BBX28 using two mutant and two transgenic lines of Arabidopsis exposed to white light and simulated shade conditions. We found that BBX28 promotes hypocotyl growth under shade through the phytochrome system by perceiving the reduction of red photons but not the reduction of photosynthetically active radiation or blue photons. We demonstrated that hypocotyl growth under shade is sustained by the protein accumulation of BBX28 in the nuclei in a CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1)-dependent manner at the end of the photoperiod. BBX28 up-regulates the expression of transcription factor- and auxin-related genes, thereby promoting hypocotyl growth under prolonged shade. Overall, our results suggest the role of BBX28 in COP1 signaling to sustain the shade-avoidance response and extend the well-known participation of other members of BBX transcription factors for fine-tuning plant growth under shade.
more »
« less
WAVE-DAMPENED2-LIKE4 modulates the hyper-elongation of light-grown hypocotyl cells
Abstract Light, temperature, water, and nutrient availability influence how plants grow to maximize access to resources. Axial growth, the linear extension of tissues by coordinated axial cell expansion, plays a central role in these adaptive morphological responses. Using Arabidopsis (Arabidopsis thaliana) hypocotyl cells to explore axial growth control mechanisms, we investigated WAVE-DAMPENED2-LIKE4 (WDL4), an auxin-induced, microtubule-associated protein and member of the larger WDL gene family shown to modulate hypocotyl growth under changing environmental conditions. Loss-of-function wdl4 seedlings exhibited a hyper-elongation phenotype under light conditions, continuing to elongate when wild-type Col-0 hypocotyls arrested and reaching 150% to 200% of wild-type length before shoot emergence. wdl4 seedling hypocotyls showed dramatic hyper-elongation (500%) in response to temperature elevation, indicating an important role in morphological adaptation to environmental cues. WDL4 was associated with microtubules under both light and dark growth conditions, and no evidence was found for altered microtubule array patterning in loss-of-function wdl4 mutants under various conditions. Examination of hormone responses showed altered sensitivity to ethylene and evidence for changes in the spatial distribution of an auxin-dependent transcriptional reporter. Our data provide evidence that WDL4 regulates hypocotyl cell elongation without substantial changes to microtubule array patterning, suggesting an unconventional role in axial growth control.
more »
« less
- Award ID(s):
- 1927504
- PAR ID:
- 10438396
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Plant Physiology
- Volume:
- 192
- Issue:
- 4
- ISSN:
- 0032-0889
- Format(s):
- Medium: X Size: p. 2687-2702
- Size(s):
- p. 2687-2702
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Summary Isogenic individuals can display seemingly stochastic phenotypic differences, limiting the accuracy of genotype‐to‐phenotype predictions. The extent of this phenotypic variation depends in part on genetic background, raising questions about the genes involved in controlling stochastic phenotypic variation.Focusing on early seedling traits inArabidopsis thaliana, we found that hypomorphs of the cuticle‐related geneLIPID TRANSFER PROTEIN 2(LTP2) greatly increased variation in seedling phenotypes, including hypocotyl length, gravitropism and cuticle permeability. Manyltp2hypocotyls were significantly shorter than wild‐type hypocotyls while others resembled the wild‐type.Differences in epidermal properties and gene expression betweenltp2seedlings with long and short hypocotyls suggest a loss of cuticle integrity as the primary determinant of the observed phenotypic variation. We identified environmental conditions that reveal or mask the increased variation inltp2hypomorphs and found that increased expression of its closest paralogLTP1is necessary forltp2phenotypes.Our results illustrate how decreased expression of a single gene can generate starkly increased phenotypic variation in isogenic individuals in response to an environmental challenge.more » « less
-
Abstract While moderately elevated ambient temperatures do not trigger stress responses in plants, they do substantially stimulate the growth of specific organs through a process known as thermomorphogenesis. The basic helix–loop–helix transcription factor PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) plays a central role in regulating thermomorphogenetic hypocotyl elongation in various plant species, including Arabidopsis (Arabidopsis thaliana). Although it is well known that PIF4 and its co-activator HEMERA (HMR) promote plant thermosensory growth by activating genes involved in the biosynthesis and signaling of the phytohormone auxin, the detailed molecular mechanism of such transcriptional activation is not clear. In this report, we investigated the role of the Mediator complex in the PIF4/HMR-mediated thermoresponsive gene expression. Through the characterization of various mutants of the Mediator complex, a tail subunit named MED14 was identified as an essential factor for thermomorphogenetic hypocotyl growth. MED14 was required for the thermal induction of PIF4 target genes but had a marginal effect on the levels of PIF4 and HMR. Further transcriptomic analyses confirmed that the expression of numerous PIF4/HMR-dependent, auxin-related genes required MED14 at warm temperatures. Moreover, PIF4 and HMR physically interacted with MED14 and both were indispensable for the association of MED14 with the promoters of these thermoresponsive genes. While PIF4 did not regulate MED14 levels, HMR was required for the transcript abundance of MED14. Taken together, these results unveil an important thermomorphogenetic mechanism, in which PIF4 and HMR recruit the Mediator complex to activate auxin-related growth-promoting genes when plants sense moderate increases in ambient temperature.more » « less
-
Plant roots elongate when cells produced in the apical meristem enter a transient period of rapid expansion. To measure the dynamic process of root cell expansion in the elongation zone, we captured digital images of growing Arabidopsis roots with horizontal microscopes and analyzed them with a custom image analysis program (PatchTrack) designed to track the growth-driven displacement of many closely spaced image patches. Fitting a flexible logistics equation to patch velocities plotted versus position along the root axis produced the length of the elongation zone (mm), peak relative elemental growth rate (% h−1), the axial position of the peak (mm from the tip), and average root elongation rate (mm h−1). For a wild-type root, the average values of these kinematic traits were 0.52 mm, 23.7% h−1, 0.35 mm, and 0.1 mm h−1, respectively. We used the platform to determine the kinematic phenotypes of auxin transport mutants. The results support a model in which the PIN2 auxin transporter creates an area of expansion-suppressing, supraoptimal auxin concentration that ends 0.1 mm from the quiescent center (QC), and that ABCB4 and ABCB19 auxin transporters maintain expansion-limiting suboptimal auxin levels beginning approximately 0.5 mm from the QC. This study shows that PatchTrack can quantify dynamic root phenotypes in kinematic terms.more » « less
-
Summary Style length is a major determinant of breeding strategies in flowering plants and can vary dramatically between and within species. However, little is known about the genetic and developmental control of style elongation.We characterized the role of two classes of leaf adaxial–abaxial polarity factors, SUPPRESSOR OF GENE SILENCING3 (SGS3) and the YABBY family transcription factors, in the regulation of style elongation inMimulus lewisii. We also examined the spatiotemporal patterns of auxin response during style development.Loss ofSGS3function led to reduced style length via limiting cell division, and downregulation ofYABBYgenes by RNA interference resulted in shorter styles by decreasing both cell division and cell elongation. We discovered an auxin response minimum between the stigma and ovary during the early stages of pistil development that marks style differentiation. Subsequent redistribution of auxin response to this region was correlated with style elongation. Auxin response was substantially altered when bothSGS3andYABBYfunctions were disrupted.We suggest that auxin signaling plays a central role in style elongation and that the way in which auxin signaling controls the different cell division and elongation patterns underpinning natural style length variation is a major question for future research.more » « less
