Photosynthesis is a complex pathway in which light energy and water are used to fix carbon, in the form of carbon dioxide, into sugar with an oxygen by-product. Plants, algae, and cyanobacteria rely on this process to produce their own source of energy, while we benefit from the creation and maintenance of both the Earth’s oxygen content and the primary source of food.

There are three types of photosynthesis, defined by the carbon fixation pathways used: C3, C4 and CAM.

Plants with C4 photosynthesis have evolved independently45不同的时间throughout the history of flowering plants. However, only about 7600 plant species, or 3% of all known plant species, use this pathway. Evolution of theC4途径涉及叶子解剖学，基因表达，细胞生物学和生物化学的改变。

But C4 plants have a competitive edge over C3 plants: they use 3-fold less water, allowing them to grow in conditions of drought, high temperature, and carbon dioxide limitation.

Many researchers are now focused on understanding the differences between C3 and C4 plants, in an attempt to engineer important crops to be more energy and water efficient. Only four major crops use C4 photosynthesis: maize, sugar cane, sorghum, and millet.

However, there are bioengineering projects underway with the aim of increasing productivity infoodandbiofuels. To understand the evolution of C4 metabolism and how it can be engineered, we need to have genomic and transcriptomic information from closely related C3 and C4 species.

Comparisons between C3 and C4 plants have mostly focused on the known C4 crops and important C3 crops like rice and wheat. But the two groups are not very closely related, having diverged 50 million years ago. Distant evolutionary relationships can sometimes fail to detect the genomic changes associated with the evolution of C4 photosynthesis.

A recent study published inGenome Biologyby Anthony Studer and colleagues at theDonald Danforth Plant Science Centerhelps to bridge this gap by presenting the genome and transcriptome ofDichanthelium oligosanthes. This species ofpanicoid grassdiverged from maize, sorghum, and sugarcane 15 million years ago, before the evolution of C4 in that clade. In other words,D. oligosanthesis a C3 panicoid grass that is closely related to important C4 panicoid grass crops.

作者提出了基因组的质量汇编D. oligosanthes, representing 78% of the estimated total genome, but covering 98% of the coding sequence. They then looked at gene expression profiles ofD. oligosanthes在不同阶段的叶片发育阶段以及六个核心C4酶的表达模式中密切相关的小米。这对与C4途径的演变相关的基因调节的变化具有见解。

Studer and his colleagues hope that the genomic information they have provided onD. oligosanthes, the only C3 grass in a C4-rich clade, will facilitate the study of the mechanisms involved in the evolution of C4 photosynthesis. They also hopeD. oligosanthescan be used as a model for studying cold tolerance in panicoid grasses to produce heartier crops for growth in the Northern hemisphere.