Information Integration and Communication in Plant Growth Regulation

Abstract

Plants are equipped with the capacity to respond to a large number of diverse signals, both internal ones and those emanating from the environment, that are critical to their survival and adaption as sessile organisms. These signals need to be integrated through highly structured intracellular networks to ensure coherent cellular responses, and in addition, spatiotemporal actions of hormones and peptides both orchestrate local cell differentiation and coordinate growth and physiology over long distances. Further, signal interactions and signaling outputs vary significantly with developmental context. This review discusses our current understanding of the integrated intracellular and intercellular signaling networks that control plant growth.

Figure 1. Integration of Light and Hormone Signaling Pathways Regulates Hypocotyl Elongation

(A) Light and hormonal signals (red text) are perceived by cell-surface or intracellular receptors (blue), which regulate transcription factors (green) through signaling/posttranslational mechanisms (red lines), whereas the transcription factors transcriptionally regulate (blue lines) downstream responses and components of other pathways. Orange: kinases; yellow: phosphatases; purple: inhibitors of transcription factors. (B) Transcriptional integration by the BAP/D-HHbH circuit. Red and blue lines show regulation at the protein and RNA (transcriptional) levels, respectively.

Figure 2. Mechanisms that Regulate the Tradeoff between Growth and Defense

(A) Mechanisms of crosstalks of FLS2-mediated flagellin signaling with the BR and auxin pathways. (B) Growth regulation in response to herbivore attack, mediated by crosstalk between the GA and JA pathways. Red and blue lines show regulation at the protein and RNA (transcriptional) levels, respectively. Dashed lines indicate unknown mechanisms.

Figure 3. Hormone-Mediated Growth Responses to Shade

(A) Diagram of light-hormone interactions in growth regulation under full light (left) and shade (right) conditions. HBL: high blue light, LBL: low blue light, HRFR: high red:far-red ratio, LRFR: low red:far-red ratio. Dark text and arrows show active components and their activities, and dimmed text and arrows indicated inactivated components and activities. Red arrows show the flow of auxin. (B) Venn diagram shows overlaps between genes induced by 1 hr low R:FR treatment (Li et al., 2012), or by 6 hr low blue light treatment of light-grown seedlings (Pedmale et al., 2016), and the target genes of BZR1, PIF4, and ARF6 identified by ChIP-seq in dark-grown seedlings (Oh et al., 2012, 2014).

Figure 4. Signaling Networks Regulating Root Growth

(A) Image of Arabidopsis root tip showing meristem zone, transition zone, and elongation zone. Arrows indicate the auxin reflux loop. PIN1 mediates polar auxin transport from shoot to the root tip. Auxin is then transported shootward by PIN2, creating auxin maximum in the QC and auxin gradient along the root developmental zones. BR distribution shows an opposite gradient with high BR levels in the elongation zone and low levels in the QC. (B–E) Diagrams summarizing cross-regulation of root growth and development by hormones and environmental stimuli. Arrows indicate positive regulation; bars indicate negative regulation; solid lines indicate direct regulation, dashed lines indicate indirect regulation; dotted arrows indicate movement of signals.