Yes, Arabidopsis is a model organism, but for what exactly? Many would like us to believe that it is a model for all things botanical, i.e. plants. However, with those organisms newly defined as ‘photosynthetic eukaryotic organisms, including algae and possibly cyanobacteria’, that is a truly tall order for such a slight specimen! And arguably an extreme point of view (although entirely understandable if one’s past, present and future employment is tied to research grants using this beast). However, and at the other end of that spectrum of opinion, there are those who espouse the view that arabidopsis is truly only a model for, well, other arabidopses. Adding to the debate, David Pacheco-Villalobos et al. reveal that interactions between the plant hormones ethylene and auxin in roots of the monocot Brachypodium distachyon (‘another’ model plant) differ to those in roots of the dicot Arabidopsis.
Whereas lowered levels of ethylene in Arabidopsis can cause decreases in another hormone – auxin – and thus result in shorter roots, in Brachypodium decreases in ethylene lead to elevated levels of auxin and longer roots(!). The latter’s ‘inverted regulatory relation between the two hormones’ points to ‘a complex homeostatic crosstalk between auxin and ethylene in Brachypodium roots, which is fundamentally different from Arabidopsis and might be conserved in other monocotyledons’. So, and as those scientists sagely state, ‘Observations gained from model organisms are essential, yet it remains unclear to which degree they are applicable to distant relatives’. And, further complicating the ethylene story – if such was needed at this stage – ‘Scientists identify thousands of plant genes activated by ethylene gas’. Examining transcriptional response to ethylene, Katherine Chang et al. have shown that this gaseous plant hormone is involved in an extensive network of cross-regulation with many other plant hormones centred around EIN3, a transcription factor that acts as the ‘master regulator’ of the ethylene signalling pathway.
Although this work was performed in arabidopsis, EIN3 orthologs exist in many other plants, so this study is anticipated to have broader relevance to… poplar, soybean, rice, maize, moss and multicellular algae.
Updated Oct 4, as ethylene and auxin were transposed in the sentence ‘Whereas lowered levels of…’.