1480. How Did Plants That Are Resilient to Climate Warming Evolve?

Recently, a paper published in Plants, People, Planet examined how plants evolved mechanisms that allow them to tolerate high temperatures. The results suggest that these traits did not emerge all at once, but were likely built up gradually through small, pre-existing changes in their genes. In other words, plants may have been undergoing a long process of “pre-adaptation” over evolutionary time.

Among plant traits, some are “complex,” meaning they are formed by multiple components working together. Photosynthesis is one such example. These traits are thought to arise not suddenly, but through the stepwise accumulation of small changes over long periods. One well-known example is C4 photosynthesis, a system that allows plants to use carbon dioxide more efficiently under hot and high-light conditions. Compared to the standard C3 pathway, it is better suited to warmer environments, but it requires the coordinated function of many genes and cell types, making it a highly complex system.

Interestingly, although C4 photosynthesis has evolved independently many times in plants, its distribution is not random. In grasses, the group is divided into two major lineages, BOP and PACMAD, but C4 photosynthesis is found only in PACMAD species. This has led to the idea that the ancestral PACMAD lineage may have already possessed genetic features that made the evolution of C4 photosynthesis more likely.

In the study, researchers generated new genome sequences from a group of grasses called Aristidoideae, for which detailed genetic information had previously been limited, and compared them with other grass genomes to investigate these potential “preconditions.” The analysis revealed that many genetic changes had already occurred in the common ancestor of PACMAD grasses. These included gene gains, gene losses, and gene duplications, totaling more than 900 events. Although most of these changes were not directly related to C4 photosynthesis itself, they involved genes associated with functions such as molecular transport, carbon metabolism, stress protection, and gene regulation. In addition, one key enzyme involved in C4 photosynthesis, β-carbonic anhydrase, was found to have been duplicated in the PACMAD ancestor. However, such direct links to C4 photosynthesis were limited, and most changes appear to be only indirectly related.

Importantly, these genetic changes occurred before the emergence of C4 photosynthesis itself. Rather than directly creating the trait, they likely served as a preparatory stage that made later evolution possible. At the same time, there was no strong evidence for massive gene expansion or clear functional specialization, suggesting that C4 evolution was not driven by a single large genetic shift but rather by the gradual use of pre-existing genetic diversity.

In conclusion, the study proposes that complex traits such as C4 photosynthesis cannot be explained by the appearance of a single key gene. Instead, they may emerge from long-term accumulation of genetic changes that increase the likelihood of their evolution. The PACMAD lineage appears to have had such a genetic background, which may explain why C4 photosynthesis evolved repeatedly in this group. Overall, the findings highlight that evolution is not a one-time event, but a process strongly shaped by historical genetic context.

(Reference)

Pereira, L. et al., Gene turnover in the common ancestor of all C4 grasses. Plants, People, Planet (2026). https://doi.org/10.1002/ppp3.70206

Contributor: Miyuki IIYAMA, Strategic Coordination Office