News
30 Oct 2016
by Jonathan Ingram

How to build beautiful biochemical factories

What connects insects sticking to the leaves of a tobacco plant and the production of the anti-malaria drug artemisinin? The answer is trichomes – the hair-like structures on the surfaces of plants – which once seen at high magnification in a scanning electron micrograph are never forgotten for their intrinsic beauty. But these beauties are, ironically, ‘biochemical factories’ involved in the production of secondary metabolites.

How to build beautiful biochemical factories

Hairless Insight 67-18 Oct 2016 - image- RS

The hairless mutant and SRA1 protein regulation. Further detail is provided by Johannes Stratmann and Carlton Bequette in their Insight article. Johannes Stratmann and Carlton Bequette, Journal of Experimental Botany, CC0 Public Domain

By Jonathan Ingram, Journal of Experimental Botany

What connects insects sticking to the leaves of a tobacco plant and the production of the anti-malaria drug artemisinin? The answer is trichomes – the hair-like structures on the surfaces of plants – which once seen at high magnification in a scanning electron micrograph are never forgotten for their intrinsic beauty. But these beauties are, ironically, ‘biochemical factories’ involved in the production of secondary metabolites. As these couple of examples might suggest, trichomes have critically important functions and demand research attention.

A new paper by Jin-Ho Kang et al. published in Journal of Experimental Botany throws new light onto the regulation of glandular trichome formation. Johannes Stratmann and Carlton Bequette give a separate perspective on the work in their Insight article in the same issue, starting from those stranded insects to give a much wider view of the implications of this important area of research.

Molecular cloning of the tomato Hairless gene implicates actin dynamics in trichome-mediated defense and mechanical properties of stem tissue

Hairless but no longer clueless: understanding glandular trichome development

The focus of the work was the recessive hairless (hl) mutation in tomato. The name overdoes things a little, but under the light microscope the trichomes or ‘hairs’ on the aerial surfaces nevertheless present a very different appearance overall. The luxuriant hair of the wild type is replaced by something far less attractive, mangy even. But the morphological change is even more profound at the level of the individual trichome – the mutants are severely distorted. Last, the trichomes have impaired accumulation of sesquiterpene and polyphenolic compounds. All these changes mean that the tomato plants have reduced resistance to the tobacco hornworm, Manduca sexta – the larvae fed much more easily on the mutant leaves.

The WAVE regulatory complex

The authors used map-mased cloning to show that it is a mutation in the SRA1 (SPECIFICALLY RAC1-ASSOCIATED) gene which is causing the changes. Transformation of the mutant with the wild-type SRA1 sequence returned the full phenotype – from the luxuriant hair to the same level of resistance to hornworm. The SRA1 protein is a subunit of the WAVE regulatory complex (WRC), known to control the nucleation of actin filaments, which are so important in cell development.


Commenting on the research, Stratmann and Bequette note that:‘This finding is significant because it is the first report to demonstrate a role for the WRC in the development of glandular trichomes. Moreover, the WRC connects the actin-cytoskeleton network with secondary metabolism and plant defence against herbivores. It provides a lever for more in-depth studies of the molecular mechanisms underlying glandular trichome development.’

There may be practical applications which stem from this increased understanding. Stratmann and Bequette: ‘We know this is important in terms of understanding function, but as our knowledge develops it may also have wider implications … the secondary metabolites produced by trichomes have a range of practical applications. Particularly, advanced insights into WRC function could inspire breeding efforts to utilize plants as biofactories that produce desirable metabolites in their glandular trichomes.’

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Journal of Experimental Botany publishes an exciting mix of research, review and comment on fundamental questions of broad interest in plant science. Regular special issues highlight key areas.



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