Plants Outsmart Darwin

There are wonders in plants that continue to be uncovered with the tools of science.  Two recent papers in PNAS lend support to the feeling that plants are smarter than assumed.

1. Trash collection:  Humans usually only employ one trash collection service, but plants have two.  Four Chinese investigators found redundant pathways in plant cells for removing misfolded proteins.  Writing in PNAS,¹ they characterized endoplasmic reticulum associated degradation (ERAD), “an integral part of the ER quality-control system that removes toxic misfolded proteins via ubiquitin/proteasome-mediated degradation” (see 11/24/2010).  They found two genes that “function redundantly” to ensure this essential process does not fail.  The genes are conserved (unevolved) in yeast, plants, and humans.
2. Portable generators:  Humans know it is handy to have a power source, like a battery, when you’re away from the power grid.  Plants know that, too.  German scientists found that plants use potassium as a local energy source in their vessels.  Here’s what their abstract said in PNAS about how plants exploit the multi-functional potassium ion.²
   

   The essential mineral nutrient potassium (K⁺) is the most important inorganic cation for plants and is recognized as a limiting factor for crop yield and quality.  Nonetheless, it is only partially understood how K⁺ contributes to plant productivity.  K⁺ is used as a major active solute to maintain turgor and to drive irreversible and reversible changes in cell volume.  K⁺ also plays an important role in numerous metabolic processes, for example, by serving as an essential cofactor of enzymes.  Here, we provide evidence for an additional, previously unrecognized role of K⁺ in plant growth.  By combining diverse experimental approaches with computational cell simulation, we show that K⁺ circulating in the phloem serves as a decentralized energy storage that can be used to overcome local energy limitations.

   They called this the “potassium battery.”  They described how the model plant Arabidopsis “taps this ‘potassium battery,’ which then efficiently assists the plasma membrane H⁺-ATPase in energizing the transmembrane phloem (re)loading processes.”

Neither paper explained how these systems might have evolved.  The paper on ERAD degradation of misfolded proteins only mentioned that the genes are conserved, and speculated in passing about the functional differences of the ERAD genes in plants vs humans.  Another PNAS paper by Harvard biologists, however, did speculate about misfolded proteins as a source of evolutionary innovation.³  Studying how yeast cells handle misfolded proteins, they recognized that there is a fitness cost involved, as if an oarsman suddenly disabled on a rowing team makes the others have to work harder.  What does this have to do with evolution?  Not much, apparently, and maybe less: it appears to constrain evolution, not advance it:

These results underscore the distinct and evolutionarily relevant molecular threat of protein misfolding, independent of protein function.  Assuming that most misfolded proteins impose similar costs, yeast cells express almost all proteins at steady-state levels sufficient to expose their encoding genes to selection against misfolding, lending credibility to the recent suggestion that such selection imposes a global constraint on molecular evolution.

Selection against misfolding is a form of stabilizing selection – a “running in place” process that tries to maintain the status quo, not the kind of evolution Darwin envisioned.  If most mutations lead to toxic misfolded proteins, plants need to be smart enough to get rid of them quickly and systematically, not tinker with them in random searches for new functions.
    One can look in vain in this paper for any suggestions supporting old Darwinian ideas of progress, tinkering or innovation.  Quite the contrary: “Our study illustrates the value in isolating and quantifying the consequences of protein misfolding to understand their relative contributions to molecular evolution and cell biology,” they said in conclusion.  “The results support hypotheses that assume that misfolded proteins impose a selective cost independent of protein function and a model of protein quality control in which a small interacting set of proteins responds specifically to misfolded proteins in the eukaryotic cytosol.”  In the set of “hypotheses that assume that misfolded proteins impose a selective cost,” is there any reason to exclude intelligent design?

1.  Su, Liu, Xia, Hong, and Li, “Conserved endoplasmic reticulum-associated degradation system to eliminate mutated receptor-like kinases in Arabidopsis,” Proceedings of the National Academy of Sciences, published online before print December 27, 2010, doi: 10.1073/pas.1013251108.
2.  Gajdanowicz et al, “Potassium (K⁺) gradients serve as a mobile energy source in plant vascular tissues,” Proceedings of the National Academy of Sciences, published online before print December 27, 2010, doi: 10.1073/pnas.1009777108.
3.  Geiler-Samerotte et al, “Misfolded proteins impose a dosage-dependent fitness cost and trigger a cytosolic unfolded protein response in yeast,” Proceedings of the National Academy of Sciences, published online before print December 27, 2010, doi: 10.1073/pnas.1017570108.

These papers have intelligent design shouting and Darwin whimpering.  Respect your garden by acknowledging the design so clearly evident, and honoring the Designer.  Don’t insult your plants by thinking they got where they are by unguided, directionless, chance processes of evolution.  It would be like insulting professionals for a job well done by shrugging your shoulders and saying, “Stuff happens.”