Un nuevo estudio proporciona un marco para impulsar el crecimiento de los cultivos mediante la incorporación de una estrategia adoptada a partir de una especie de alga verde de rápido crecimiento. Las algas, conocidas como Chlamydomonas reinhardtii, contienen un orgánulo llamado pirenoide que acelera la conversión de carbono, que las algas absorben del aire, en una forma que los organismos pueden usar para crecer. En un estudio publicado el 19 de mayo de 2022 en la revista Nature Plants , investigadores de la Universidad de Princeton y la Universidad de Northwestern utilizaron modelos moleculares para identificar las características del pirenoide que son más críticas para mejorar la fijación de carbono, y luego mapearon cómo esta funcionalidad podría incorporarse a las plantas de cultivo.

Esto no es solo un ejercicio académico. Para muchas personas hoy en día, la mayor parte de las calorías de los alimentos provienen de plantas de cultivo domesticadas hace miles de años. Desde entonces, los avances en el riego, la fertilización, la cría y la industrialización de la agricultura han ayudado a alimentar a la creciente población humana. Sin embargo, por ahora solo se pueden extraer ganancias incrementales de estas tecnologías. Mientras tanto, se pronostica que la inseguridad alimentaria, que ya se encuentra en niveles críticos para gran parte de la población mundial, empeorará debido al cambio climático.

La nueva tecnología podría revertir esta tendencia. Muchos científicos creen que el pirenoide de algas ofrece tal innovación. Si los científicos pueden diseñar una capacidad similar a la de los pirenoides para concentrar carbono en plantas como el trigo y el arroz, estas importantes fuentes de alimentos podrían experimentar un gran impulso en sus tasas de crecimiento.

"Este trabajo proporciona una guía clara para diseñar un mecanismo de concentración de carbono en las plantas, incluidos los cultivos principales", dijo Martin Jonikas, autor principal del estudio, profesor asociado de biología molecular en Princeton e investigador en el Instituto Médico Howard Hughes. .

Chlamydomonas reinhardtii consigue la fijación de carbono gracias a la acción de la enzima Rubisco, que cataliza la conversión de 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 concentration. 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."