Approximately one-third of global CO₂ assimilation is performed by the pyrenoid, a liquid-like organelle found in most algae and some plants. Specialized pyrenoid-traversing membranes are hypothesized to drive CO₂ assimilation in the pyrenoid by delivering concentrated CO₂, but how these membranes are made to traverse the pyrenoid matrix remains unknown. Here we show that proteins SAGA1 and MITH1 cause membranes to traverse the pyrenoid matrix in the model alga Chlamydomonas reinhardtii. Mutants deficient in SAGA1 or MITH1 lack matrix-traversing membranes and exhibit growth defects under CO₂-limiting conditions. Expression of SAGA1 and MITH1 together in a heterologous system, the model plant Arabidopsis thaliana, produces matrix-traversing membranes. Both proteins localize to matrix-traversing membranes. SAGA1 binds to the major matrix component, Rubisco, and is necessary to initiate matrix-traversing membranes. MITH1 binds to SAGA1 and is necessary for extension of membranes through the matrix. Our data suggest that SAGA1 and MITH1 cause membranes to traverse the matrix by creating an adhesive interaction between the membrane and matrix. Our study identifies and characterizes key factors in the biogenesis of pyrenoid matrix-traversing membranes, demonstrates the importance of these membranes to pyrenoid function and marks a key milestone toward pyrenoid engineering into crops for improving yields.

全球大约三分之一的 CO₂ 同化由类除焦烯完成，吡嘌类化合物是一种液体状细胞器，存在于大多数藻类和一些植物中。据推测，专门的类焦体遍历膜通过输送浓缩的 CO₂ 来驱动 CO₂ 在类焦体中同化，但这些膜是如何穿过类焦体基质的仍然未知。在这里，我们表明蛋白质 SAGA1 和 MITH1 导致膜穿过模型藻类衣藻中的类散体基质莱茵衣藻。SAGA1 或 MITH1 缺陷的突变体缺乏基质穿越膜，并且在 CO₂ 限制条件下表现出生长缺陷。SAGA1 和 MITH1 在异源系统（模式植物拟南芥）中一起表达，产生基质横穿膜。两种蛋白质都定位于基质遍历膜。SAGA1 与主要基质成分 Rubisco 结合，是启动基质遍历膜所必需的。MITH1 与 SAGA1 结合，是膜通过基质延伸所必需的。我们的数据表明，SAGA1 和 MITH1 通过在膜和基质之间产生粘附相互作用，导致膜穿过基质。我们的研究确定并表征了类核细胞基质横穿膜生物发生的关键因素，证明了这些膜对类核细胞功能的重要性，并标志着核核细胞工程化到作物中以提高产量的关键里程碑。