Soil salinity inhibits plant shade avoidance

Global food production is set to keep increasing despite a predicted decrease in total arable land. To achieve higher production, denser planting will be required on increasingly degraded soils. When grown in dense stands, crops elongate and raise their leaves in an effort to reach sunlight, a process termed shade-avoidance. Shade is perceived by a reduction in the ratio of red (R) to (FR) light and results in the stabilisation of a class of transcription factors known as PHYTOCHROME INTERACTING FACTORs (PIFs). PIFs activate the expression of auxin biosynthesis genes and enhance auxin sensitivity, which promotes cell wall loosening and drives elongation growth. Despite our molecular understanding of shade-induced growth, little is known about how this developmental programme is integrated with other environmental factors. Here we demonstrate that low levels of NaCl in soil strongly impair the ability of plants to respond to shade. This block is dependent upon abscisic acid (ABA) signalling and the canonical ABA signalling pathway. Low R:FR light enhances the expression of a positive regulator of the brassinosteroid (BR) signalling pathway, BRASSINOSTEROID SIGNALLING KINASE 5 (BSK5). We found that ABA inhibits BSK5 up-regulation and interferes with GSK3-like kinase inactivation by the BR pathway, thus leading to a suppression of PIF function. By demonstrating a link between the ABA and BR-signalling pathways this study provides an important step forward in our understanding of how environmental cues are integrated into plant development

AGC kinases and MAB4/MEL proteins maintain PIN polarity by limiting lateral diffusion in plant cells

Polar subcellular localization of the PIN exporters of the phytohormone auxin is a key determinant of directional, intercellular auxin transport and thus a central topic of both plant cell and developmental biology. Arabidopsis mutants lacking PID, a kinase that phosphorylates PINs, or the MAB4/MEL proteins of unknown molecular function display PIN polarity defects and phenocopy pin mutants, but mechanistic insights into howthese factors convey PIN polarity are missing. Here, by combining protein biochemistry with quantitative live-cell imaging, we demonstrate that PINs, MAB4/MELs, and AGC kinases interact in the same complex at the plasma membrane. MAB4/MELs are recruited to the plasma membrane by the PINs and in concert with the AGC kinases maintain PIN polarity through limiting lateral diffusion-based escape of PINs from the polar domain. The PIN-MAB4/MEL-PID protein complex has self-reinforcing properties thanks to positive feedback between AGC kinase-mediated PIN phosphorylation and MAB4/MEL recruitment. Wethus uncover the molecular mechanism by which AGC kinases and MAB4/MEL proteins regulate PIN localization and plant development.Plant science

A High-Five for High Light Protection

Plants cannot live without light, but they also cannot live with too much light. Beyond a certain threshold, a high light intensity will damage the photosynthetic apparatus directly. Furthermore, high light leads to the production of reactive oxygen species that can cause widespread damage in the cell (Li et al., 2009). One way in which plants respond to high light stress is by converting some of the excess light into heat via nonphotochemical quenching (NPQ; Müller et al., 2001). Outdoors, light intensities can vary greatly in time and space: one part of the plant can experience high light stress while another part is shaded. This shaded part of the plant might experience high light stress later on; therefore, it is advantageous for plants to have evolved a systemic signaling response to local high light stress that primes the whole plant to respond better to high light (Karpinski et al., 1999). Several ideas of how the plant transduces such a systemic signal have been postulated, such as a calcium or reactive oxygen species wave and abscisic acid synthesis (Gilroy et al., 2016; Devireddy et al., 2018). However, no direct links between these signaling mechanisms and NPQ systemic high light acclimation have been identified