A role for brassinosteroid signalling in decision-making processes in the Arabidopsis seedling

Abstract

Plants often adapt to adverse conditions via differential growth, whereby limited resources are discriminately allocated to optimize the growth of one organ at the expense of another. Little is known about the decision-making processes that underly differential growth. In this study, we developed a screen to identify decision making mutants by deploying two tools that have been used in decision theory: a well-defined yet limited budget, as well as conflict-of-interest scenarios. A forward genetic screen that combined light and water withdrawal was carried out. This identified BRASSINOSTEROID INSENSITIVE 2 (BIN2) alleles as decision mutants with “confused” phenotypes. An assessment of organ and cell length suggested that hypocotyl elongation occurred predominantly via cellular elongation. In contrast, root growth appeared to be regulated by a combination of cell division and cell elongation or exit from the meristem. Gain- or loss- of function bin2 mutants were most severely impaired in their ability to adjust cell geometry in the hypocotyl or cell elongation as a function of distance from the quiescent centre in the root tips. This study describes a novel paradigm for root growth under limiting conditions, which depends not only on hypocotyl-versus-root trade-offs in the allocation of limited resources, but also on an ability to deploy different strategies for root growth in response to multiple stress conditions.

Regulation of adaptive growth decisions via phosphorylation of the TRAPPII complex in Arabidopsis

“…The opposite was true for bin2-3 bil1 bil2 and trappii mutants, which were able to respond to single stress factors but not to additive stress (Fig. 4; Kalbfuß et al, 2022). Shaggy-like kinases integrate a vast number of signaling pathways (Lv & Li, 2020;Li et al, 2021;Song et al, 2023;Planas-Riverola et al, 2019).…”

“…6E-G). We have recently shown that root growth in response to water stress in the dark is due to a combination of cell division and rapid exit from the meristem (Kalbfuß et al, 2022). An early exit from the meristem can be visualized as cell elongation in cells close to the quiescent center.…”

“…To avoid such controversy, Severino (2021) makes the case for experimental approaches. A recent experimental approach for the study of decision-making processes in germinating seedlings has incorporated two tools used in decision theory: the use of a limited budget and of conflict-of interest scenarios (Kalbfuß et al, 2022). A limited budget was achieved by germination in the dark and a conflict-of-interest by the simultaneous withdrawal of light and water; as a binary readout for responses to these additive stress conditions, tradeoffs in hypocotyl versus root growth were monitored (Kalbfuß et al, 2022).…”

“…A recent experimental approach for the study of decision-making processes in germinating seedlings has incorporated two tools used in decision theory: the use of a limited budget and of conflict-of interest scenarios (Kalbfuß et al, 2022). A limited budget was achieved by germination in the dark and a conflict-of-interest by the simultaneous withdrawal of light and water; as a binary readout for responses to these additive stress conditions, tradeoffs in hypocotyl versus root growth were monitored (Kalbfuß et al, 2022). By emphasizing growth trade-offs, the experimental approach developed by Kalbfuß et al (2022) is aligned with the definition of decisionmaking as entailing an appraisal of the advantages and disadvantages of various courses of action (Karban & Orrock, 2018).…”

“…A limited budget was achieved by germination in the dark and a conflict-of-interest by the simultaneous withdrawal of light and water; as a binary readout for responses to these additive stress conditions, tradeoffs in hypocotyl versus root growth were monitored (Kalbfuß et al, 2022). By emphasizing growth trade-offs, the experimental approach developed by Kalbfuß et al (2022) is aligned with the definition of decisionmaking as entailing an appraisal of the advantages and disadvantages of various courses of action (Karban & Orrock, 2018). While Kalbfuß et al (2022) address decision-making at a cellular level, the literature on plant decision-making has, to our knowledge, not included considerations about the possible role of the TGN.…”