How did the East Asian summer monsoon shape the genomic evolution of Engelhardia?

The East Asian Summer Monsoon (EASM) is a key climatic driver shaping ecosystems in East Asia by regulating water and heat patterns. Its fluctuations over geological times have influenced vegetation types and species adaptation. In particular, subtropical evergreen broad-leaved forests (EBLFs) have expanded significantly due to the EASM, contributing to biodiversity and providing vital ecological services. However, the genomic mechanisms behind plant adaptation to the EASM remain largely unexplored. Understanding these mechanisms is essential for uncovering how plant species have historically responded to monsoon-driven climate shifts and how they continue to adapt to ongoing environmental changes.

To investigate this, Dr. Hong-Hu Meng and colleagues from the Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, focused on the genus Engelhardia, a common and characteristic component of China's EBLFs, which spans multiple ecological zones from tropical rainforests to subtropical forests.

The team's findings were published as a cover article in the KeAi journal Plant Diversity under the title of "Genome analyses provide insights into Engelhardia’s adaptation to East Asia Summer Monsoon".

This work started with the sequencing of genomes of five Engelhardia species and the closely related Rhoiptelea chiliantha using PacBio HiFi and Hi-C. The resulting high-quality assemblies revealed substantial variation in genome size (414.56–985.85 Mb) and gene number (31,000–53,000).

“Phylogenomic analyses estimate the divergence between the evergreen lineages (E. fenzelii, E. roxburghiana) and the deciduous lineage (E. spicata) at approximately 52 Mya,” shares Meng. “A subsequent separation between E. fenzelii and E. roxburghiana occurred around 25 Mya, coinciding with the intensification of the EASM, which likely drove the transition from deciduous to evergreen forest ecosystems in Asia.”

Gene family analyses further support this divergence, revealing functional differentiation between the lineages. “Evergreen species have expanded genes related to photosynthesis, hormone signaling, and redox processes, whereas deciduous species have prioritized genes involved in drought response,” says Meng.

Notably, E. fenzelii exhibits a significant expansion of the TPS gene family, which likely contributes to its enhanced survival in humid, competitive environments. “Additionally, transposable elements play a key role in the larger genome size of E. fenzelii, further facilitating its adaptation to the moist, monsoonal climate,” adds Meng.

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Contact the author: Contact the author: Hong-Hu Meng, menghonghu@xtbg.ac.cn

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