Hvordan hurtigtvoksende alger kan øge væksten af ​​fødevareafgrøder

En ny undersøgelse giver en ramme for at øge afgrødevæksten ved at inkorporere en strategi, der er vedtaget fra en hurtigtvoksende art af grønne alger. Algerne, kendt som Chlamydomonas reinhardtii, indeholder en organel kaldet pyrenoiden, der fremskynder omdannelsen af ​​kulstof, som algerne optager fra luften, til en form, som organismerne kan bruge til vækst. I en undersøgelse offentliggjort 19. maj 2022 i tidsskriftet Nature Plants , brugte forskere ved Princeton University og Northwestern University molekylær modellering til at identificere de funktioner i pyrenoiden, der er mest kritiske for at forbedre kulstoffikseringen, og kortlagde derefter, hvordan denne funktionalitet kunne konstrueres til afgrødeplanter.

Dette er ikke kun en akademisk øvelse. For mange mennesker i dag kommer hovedparten af ​​madkalorierne fra afgrødeplanter, der blev tæmmet for tusinder af år siden. Siden da har fremskridt inden for kunstvanding, befrugtning, avl og industrialiseringen af ​​landbruget hjulpet med at brødføde den spirende menneskelige befolkning. Men på nuværende tidspunkt kan kun trinvise gevinster udvindes fra disse teknologier. I mellemtiden forudsiges fødevareusikkerhed, der allerede er på kriseniveau for en stor del af verdens befolkning, at blive værre på grund af et skiftende klima.

Ny teknologi kan vende denne tendens. Mange forskere mener, at algepyrenoiden tilbyder netop en sådan innovation. Hvis videnskabsmænd kan konstruere en pyrenoid-lignende evne til at koncentrere kulstof i planter som hvede og ris, kan disse vigtige fødekilder opleve et stort løft til deres væksthastigheder.

"Dette arbejde giver klar vejledning til at konstruere en kulstofkoncentrerende mekanisme i planter, herunder større afgrøder," sagde Martin Jonikas, en seniorforfatter af undersøgelsen, som er lektor i molekylærbiologi ved Princeton og en efterforsker ved Howard Hughes Medical Institute .

Chlamydomonas reinhardtii opnår kulstoffiksering på grund af virkningen af ​​enzymet Rubisco, som katalyserer omdannelsen af ​​CO₂ into organic carbon.

Terrestrial plants also use Rubisco to accomplish carbon fixation, but in most plants, Rubisco only works at about a third of its theoretical capacity because it cannot access enough CO₂ to operate faster. Much effort has therefore gone into studying the carbon-concentrating mechanisms, particularly those found in cyanobacteria and in Chlamydomonas, with the hope of eventually providing this function for terrestrial crop plants. But there's a problem:

"While the structure of the pyrenoid and many of its components are known, key biophysical questions about its mechanism remain unanswered, due to a lack of quantitative and systematic analysis," said senior co-author Ned Wingreen, Princeton's Howard A. Prior Professor of the Life Sciences and professor of molecular biology and the Lewis-Sigler Institute of Integrative Genomics.

To gain insights about how the algal pyrenoid carbon-concentrating mechanism works, Princeton graduate student Chenyi Fei collaborated with undergraduate Alexandra Wilson, Class of 2020, to develop a computational model of the pyrenoid with the help of co-author Niall Mangan, assistant professor of engineering sciences and applied mathematics at Northwestern University.

Prior work has shown that the Chlamydomonas reinhardtii pyrenoid consists of a spherical Rubisco matrix traversed by a vasculature of membrane-enclosed projections called pyrenoid tubules, and surrounded by a sheath made of starch. It's thought that CO₂ taken up from the environment is converted into bicarbonate and then transported into the tubules, where it then enters the pyrenoid. An enzyme present in the tubules converts bicarbonate back into CO₂ , which then diffuses into the Rubisco matrix. But is this picture complete?

"Our model demonstrates that this conventional picture of the pyrenoid carbon-concentrating mechanism can't work because CO₂ would just rapidly leak back out of the pyrenoid before Rubisco could act on it," Wingreen said. "Instead, the starch shell around the pyrenoid must act as a diffusion barrier to trap CO₂ in the pyrenoid with Rubisco."

In addition identifying this diffusion barrier, the researchers' model pinpointed other proteins and structural features needed for CO₂ koncentration. The model also identified non-necessary components, which should make engineering pyrenoid functionality into plants a simpler task. This simplified model of the pyrenoid, the researchers showed, behaves similarly to the actual organelle.

"The new model developed by Fei, Wilson, and colleagues is a game changer," said Alistair McCormick, an expert in Plant Molecular Physiology and Synthetic Biology at the University of Edinburgh, who has worked with the Princeton scientists but was not involved in this study.

"One of the key findings of this paper, which differentiates the Chlamydomonas carbon-concentrating mechanism from those found in cyanobacteria, is that introducing active bicarbonate transporters may not be necessary," McCormick said. "This is important because active bicarbonate transport has been a key challenge hindering progress in the engineering of biophysical carbon-concentrating mechanisms."