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Time-lapse imaging of roots is highly suitable for depicting gravitropic growth behaviors. However, roots may show faster or slower bending kinetics when compared to control as a result of differences in overall root growth. Accordingly, conditions that cause differential organ growth require growth rate normalization to compare gravitropic curvature. Here, we describe a simple normalization method for gravitropic root growth evaluation. We exemplify this method by exposing seedlings to distinct environmental conditions or disturbing the cellular auxin contents. This data shows that the method is suitable to discriminate between gravitropic and overall organ growth defects.

Multiple internal and external signals modulate the metabolism, intercellular transport and signaling of the phytohormone auxin. Considering this complexity, it remains largely unknown how plant cells monitor and ensure the homeostasis of auxin responses. PINLIKES (PILS) intracellular auxin transport facilitators at the endoplasmic reticulum are suitable candidates to buffer cellular auxin responses because they limit nuclear abundance and signaling of auxin. We used forward genetics to identify gloomy and shiny pils (gasp) mutants that define the PILS6 protein abundance in a posttranslational manner. Here, we show that GASP1 encodes an uncharacterized RING/U-box superfamily protein that impacts on auxin signaling output. The low auxin signaling in gasp1 mutants correlates with reduced abundance of PILS5 and PILS6 proteins. Mechanistically, we show that high and low auxin conditions increase and reduce PILS6 protein levels, respectively. Accordingly, nonoptimum auxin concentrations are buffered by alterations in PILS6 abundance, consequently leading to homeostatic auxin output regulation. We envision that this feedback mechanism provides robustness to auxin-dependent plant development. [ABSTRACT FROM AUTHOR]

Temperature modulates growth and development throughout the entire lifecycle of a plant. High temperature (HT) triggers the auxin biosynthesis-dependent growth in aerial tissues. On the other hand, the contribution of auxin to HT-induced root growth is currently under debate. Here we show that the putative intracellular auxin carrier PIN-LIKES 6 (PILS6) is a negative regulator of organ growth and that its abundance is highly sensitive to HT. PILS6 localizes to the endoplasmic reticulum and limits the nuclear availability of auxin, consequently reducing the auxin signaling output. HT represses the PILS6 protein abundance, which impacts on PILS6-dependent auxin signaling in roots and root expansion. Accordingly, we hypothesize that PILS6 is part of an alternative mechanism linking HT to auxin responses in roots. [ABSTRACT FROM AUTHOR]

Summary: A central question in developmental biology concerns the mechanism of generation and maintenance of cell polarity, because these processes are essential for many cellular functions and multicellular development []. In plants, cell polarity has an additional role in mediating directional transport of the plant hormone auxin that is crucial for multiple developmental processes []. In addition, plant cells have a complex extracellular matrix, the cell wall [], whose role in regulating cellular processes, including cell polarity, is unexplored. We have found that polar distribution of PIN auxin transporters [] in plant cells is maintained by connections between polar domains at the plasma membrane and the cell wall. Genetic and pharmacological interference with cellulose, the major component of the cell wall, or mechanical interference with the cell wall disrupts these connections and leads to increased lateral diffusion and loss of polar distribution of PIN transporters for the phytohormone auxin. Our results reveal a plant-specific mechanism for cell polarity maintenance and provide a conceptual framework for modulating cell polarity and plant development via endogenous and environmental manipulations of the cellulose-based extracellular matrix. [Copyright &y& Elsevier]

The article discusses the significance of polar targeting on plant development. It is noted that the mechanisms underlying the establishment and maintenance of cell polarity belong to the important themes of developmental and cell biology. It is stated that plant polarity is determined at the cellular level and is tightly connected to the polarity of tissues and organs. Furthermore, the plant hormone auxin is considered an important factor that mediates tissue and organ polarity in plants.

Auxin and brassinosteroids (BR) are crucial growth regulators and display overlapping functions during plant development. Here, we reveal an alternative phytohormone crosstalk mechanism, revealing that BR signaling controls PIN-LIKES (PILS)-dependent nuclear abundance of auxin. We performed a forward genetic screen for imperial pils (imp) mutants that enhance the overexpression phenotypes of PILS5 putative intracellular auxin transport facilitator. Here, we report that the imp1 mutant is defective in the BR-receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1). Our set of data reveals that BR signaling transcriptionally and post-translationally represses the accumulation of PILS proteins at the endoplasmic reticulum, thereby increasing nuclear abundance and signaling of auxin. We demonstrate that this alternative phytohormonal crosstalk mechanism integrates BR signaling into auxin-dependent organ growth rates and likely has widespread importance for plant development. • Impaired BR perception enhances PILS5 overexpression phenotypes • BR signaling increases PILS protein turnover • BR signaling defines PILS-dependent nuclear abundance and signaling of auxin • PILS-dependent BR-auxin crosstalk affects organ growth Sun et al. reveal that BR signaling limits the accumulation of PILS proteins at the endoplasmic reticulum, thereby increasing nuclear abundance and signaling of auxin. This alternative phytohormonal crosstalk mechanism integrates BR signaling into auxin-dependent organ growth rates and likely has widespread importance for plant development. [ABSTRACT FROM AUTHOR]

Summary The emergence and radiation of multicellular land plants was driven by crucial innovations to their body plans [ 1 ]. The directional transport of the phytohormone auxin represents a key, plant-specific mechanism for polarization and patterning in complex seed plants [ 2–5 ]. Here, we show that already in the early diverging land plant lineage, as exemplified by the moss Physcomitrella patens , auxin transport by PIN transporters is operational and diversified into ER-localized and plasma membrane-localized PIN proteins. Gain-of-function and loss-of-function analyses revealed that PIN-dependent intercellular auxin transport in Physcomitrella mediates crucial developmental transitions in tip-growing filaments and waves of polarization and differentiation in leaf-like structures. Plasma membrane PIN proteins localize in a polar manner to the tips of moss filaments, revealing an unexpected relation between polarization mechanisms in moss tip-growing cells and multicellular tissues of seed plants. Our results trace the origins of polarization and auxin-mediated patterning mechanisms and highlight the crucial role of polarized auxin transport during the evolution of multicellular land plants. [ABSTRACT FROM AUTHOR]