Gatersleben, Germany
October 12, 2020
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The inflorescences of grasses often have very different shapes. An international research team led by IPK has now succeeded in identifying a gene that plays a decisive role in ensuring that barleydevelops itscharacteristic slender inflorescences, called spikes. Compared to other grasses, the COMPOSITUM1 (COM1) gene has acquired a new function during grass evolution. The results have today been published in Nature Communications magazine.
The "spikelet meristem" (SM) plays a central role duringthe development of the grass inflorescence. Meristems are plant cells or tissues that have the capacity toproduce new organs -in this case spikelets. To do this, however, cells destined to become SM must first attainthe SM identity. This is achieved, among other things, by gene regulation. As a result, cells develop normally from meristem to organ. The process thus runs from the undifferentiated plant cell to the differentiated organ.
To better understand grass inflorescence architecture, mutants can be very revealing to geneticists. The COM1 barleymutant e.g. is compromisedin a way that the corresponding cells cannot perceive or convertthe SM identity signal. "Ultimately, the signal transmission does not function properly, so that the cells cannot attaintheir correct cell identity," explainsDr. Naser Poursarebani,first-author of the study and discovererof the COM1 gene. To put it simple, the cell does not know what to do in this situation. "Thus, spikelet formation along the main axisof the barley spike, the rachis, cannot proceed normally.”
Ultimately, instead of producing a spikelet, a kind of "branch" occursthatlooks like a small secondary spike. "Such ‘branching’, however, is very untypical for all spike-forming grassesbelonging to the tribe Triticeae", Prof. Dr. Thorsten Schnurbusch, head of the independent researchgroup Plant Architecture,HEISENBERG Professor of the IPK and the Martin Luther University Halle-Wittenberg and initiator of the studyconfirms.
In barley, COM1 normally ensures that meristem cells develop into spikelets by influencing the properties of theircell walls and thus ultimately controlling cell growth. COM1's contribution to thisidentity signal is also its newly discovered function, which is not found in other grasses such as rice, maize, sorghum or twigs (Brachypodium distachyonL.). Barley COM1 function is thus fundamentally different from those above-mentioned grassspecies, in which the gene rather promotes the formation of inflorescence branches. "From a botanical point of view, COM1 is therefore in any case an important genetic factor for spike formationandshape, about which little hasbeenknown until now", explains Prof. Dr. Schnurbusch.
Barley belongs to the grass family (Poaceae) and was domesticated fromthe wild barley (Hordeum spontaneum) ancestor in the area of the Fertile Crescent about 10,000 yearsago. Scientists suspect that the simplified, less complex spikearchitecture of Triticeaespecies is related to the spread of those speciesinto zones with a more temperate climate and adaptation to cooler conditions. The newly gained insights into spike development can aidto better understand grass inflorescence evolution but possibly may also help to increase barley's yield potential.
Original publication:. Poursarebani et al. (2020), COMPOSITUM 1contributes to the architectural simplification of barley inflorescence via meristem identity signals.Nature Communications.DOI:10.1038/s41467-020-18890-y
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