Phytochrome B Controls Shoot Architecture by Regulating Phytochrome Interacting Factors and Phytohormones

Plant architectural responses to changes in the ratio of red light to far-red light (R: FR) are mediated by phytochromes (phy), especially phyB. phyB function is transduced through interactions with the PHYTOCHROME INTERACTING FACTORS (PIFs) family of transcription factors. This study assessed the roles of Arabidopsis thaliana PIF4, PIF5 and PIF7 in mediating shoot architectural responses to high and low R:FR. The genetic interactions between various PIFs and phyB were also examined. The results indicated that PIF4/PIF5 and PIF7 are required for suppression of branch outgrowth under low R:FR, or with the loss of functional phyB. Compared to wild-type, lower levels of axillary bud abscisic acid (ABA) were detected in the pif7 and pif4pif5 mutants under low R:FR. The loss of functional phyB elevated axillary bud sensitivity to exogenous ABA. It was also demonstrated that the abscisic acid biosynthetic enzyme NCED3 was essential for aspects of phyB mediated regulation of branching. The analysis of transcript abundances of a panel of auxin-responsive genes in pif and phyB mutants in the study suggested that PIF4/PIF5 may mediate branching responses by regulating the transcription of auxin-signaling genes. PIF7 mediated effects on bud outgrowth may involve regulation of both ABA abundances and sensitivity in buds. In summary, PIF4/PIF5 and PIF7 affect branching by regulating auxin-signaling in shoots, ABA biosynthesis and sensitivity in buds in response to the R:FR in coordination with phyB. Assessment of the kinetics of axillary bud outgrowth and ABA levels in buds revealed a significant change in bud ABA levels as early as 1 h after alteration of the R:FR. This indicates that buds are able to rapidly respond to variations in the R:FR. Ethylene is known to mediate plant responses to variation in the R:FR. The assessment of plant architectural changes in the ethylene insensitive mutants ein2-1 and etr1-2 revealed a minor contribution of ethylene in mediating branch outgrowth responses to the R:FR. EIN2 and ETR1 were shown to regulate normal gravitropic responses in rosette branches

Physiology and transcriptomics of water-deficit stress responses in wheat cultivars TAM 111 and TAM 112

Citation: Reddy, S. K., Liu, S., Rudd, J. C., Xue, Q., Payton, P., Finlayson, S. A., … Lu, N. (2014). Physiology and transcriptomics of water-deficit stress responses in wheat cultivars TAM 111 and TAM 112. Retrieved from http://krex.ksu.eduHard red winter wheat crops on the U.S. Southern Great Plains often experience moderate to severe drought stress, especially during the grain filling stage, resulting in significant yield losses. Cultivars TAM 111 and TAM 112 are widely cultivated in the region, share parentage and showed superior but distinct adaption mechanisms under water-deficit (WD) conditions. Nevertheless, the physiological and molecular basis of their adaptation remains unknown. A greenhouse study was conducted to understand the differences in the physiological and transcriptomic responses of TAM 111 and TAM 112 to WD stress. Whole-plant data indicated that TAM 112 used more water, produced more biomass and grain yield under WD compared to TAM 111. Leaf-level data at the grain filling stage indicated that TAM 112 had elevated abscisic acid (ABA) content and reduced stomatal conductance and photosynthesis as compared to TAM 111. Sustained WD during the grain filling stage also resulted in greater flag leaf transcriptome changes in TAM 112 than TAM 111. Transcripts associated with photosynthesis, carbohydrate metabolism, phytohormone metabolism, and other dehydration responses were uniquely regulated between cultivars. These results suggested a differential role for ABA in regulating physiological and transcriptomic changes associated with WD stress and potential involvement in the superior adaptation and yield of TAM 112

Flower orientation influences floral temperature, pollinator visits and plant fitness

Effective insect pollination requires appropriate responses to internal and external environmental cues in both the plant and the pollinator. Helianthus annuus, a highly outcrossing species, is marked for its uniform eastward orientation of mature pseudanthia, or capitula. Here we investigate how this orientation affects floral microclimate and the consequent effects on plant and pollinator interactions and reproductive fitness. We artificially manipulated sunflower capitulum orientation and temperature in both field and controlled conditions and assessed flower physiology, pollinator visits, seed traits and siring success. East-facing capitula were found to have earlier style elongation, pollen presentation and pollinator visits compared with capitula manipulated to face west. East-facing capitula also sired more offspring than west-facing capitula and under some conditions produced heavier and better-filled seeds. Local ambient temperature change on the capitulum was found to be a key factor regulating the timing of style elongation, pollen emergence and pollinator visits. These results indicate that eastward capitulum orientation helps to control daily rhythms in floral temperature, with direct consequences on the timing of style elongation and pollen emergence, pollinator visitation, and plant fitness.University of Virginia; Division of Integrative Organismal Systems; University of California Berkeley; US Department of Agriculture-National Institute of Food and Agriculture.http://www.newphytologist.comhj2022Plant Production and Soil Scienc

The timing of low R: FR exposure profoundly affects Arabidopsis branching responses

The ratio of Red to Far Red light (R:FR) is sensed by phytochromes, including phytochrome B, and serves as a signal of potential competition. Low R:FR represses Arabidopsis thaliana branching by promoting the accumulation of abscisic acid in the young buds and by enhancing auxin signaling in the main shoot. While overall plant level branching is reduced by low R:FR, the growth of the uppermost branches tends to be promoted while the lower buds are suppressed. Buds at intermediate positions can show either growth promotion or growth suppression by low R:FR if they become exposed to low R:FR late or early, respectively. This pattern suggests that developmental stage specific programming occurs to modify the response of specific buds to branching regulators including auxin and ABA.Fil: Reddy, Srirama Krishna. Texas A&M University; Estados UnidosFil: Holalu, Srinidhi V.. Texas A&M University; Estados UnidosFil: Casal, Jorge Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Finlayson, Scott A.. Texas A&M University; Estados Unido

Two MYB Proteins in a Self-Organizing Activator-Inhibitor System Produce Spotted Pigmentation Patterns

Many organisms exhibit visually striking spotted or striped pigmentation patterns. Developmental models predict that such spatial patterns can form when a local autocatalytic feedback loop and a long-range inhibitory feedback loop interact. At its simplest, this self-organizing network only requires one self-activating activator that also activates a repressor, which inhibits the activator and diffuses to neighboring cells. However, the molecular activators and inhibitors fully fitting this versatile model remain elusive in pigmentation systems. Here, we characterize an R2R3-MYB activator and an R3-MYB repressor in monkeyflowers (Mimulus). Through experimental perturbation and mathematical modeling, we demonstrate that the properties of these two proteins correspond to an activator-inhibitor pair in a two-component, reaction-diffusion system, explaining the formation of dispersed anthocyanin spots in monkeyflower petals. Notably, disrupting this pattern impacts pollinator visitation. Thus, subtle changes in simple activator-inhibitor systems are likely essential contributors to the evolution of the remarkable diversity of pigmentation patterns in flowers