No abstract

Serine/arginine-rich (SR) proteins are important splicing factors in plant development and abiotic/hormone-related stresses. However, evidence that SR proteins contribute to the process in woody plants has been lacking. Using phylogenetics, gene synteny, transgenic experiments, and RNA-seq analysis, we identified 24 PtSR genes and explored their evolution, expression, and function in Popolus trichocarpa. The PtSR genes were divided into six subfamilies, generated by at least two events of genome triplication and duplication. Notably, they were constitutively expressed in roots, stems, and leaves, demonstrating their fundamental role in P. trichocarpa. Additionally, most PtSR genes (~83%) responded to at least one stress (cold, drought, salt, SA, MeJA, or ABA), and, especially, cold stress induced a dramatic perturbation in the expression and/or alternative splicing (AS) of 18 PtSR genes (~75%). Evidentially, the overexpression of PtSCL30 in Arabidopsis decreased freezing tolerance, which probably resulted from AS changes of the genes (e.g., ICE2 and COR15A) critical for cold tolerance. Moreover, the transgenic plants were salt-hypersensitive at the germination stage. These indicate that PtSCL30 may act as a negative regulator under cold and salt stress. Altogether, this study sheds light on the evolution, expression, and AS of PtSR genes, and the functional mechanisms of PtSCL30 in woody plants.

The C‐repeat binding factors/dehydration‐responsive element binding protein 1s (CBFs/DREB1s) have been identified as major regulators of cold acclimation in many angiosperm plants. However, their origin and evolutionary process associated to cold responsiveness are still lacking. By integrating multi‐omics data of genomes, transcriptomes, and CBFs/DREB1s genome‐wide binding profiles, we unveil the origin and evolution of CBFs/DREB1s and their regulatory network. Gene collinearity and phylogeny analyses show that CBF/DREB1 is an innovation evolved from tandem duplication‐derived DREB III gene. A subsequent event of ε‐whole genome duplication led to two CBF/DREB1 archetypes (Clades I and II) in ancient angiosperms. In contrast to cold‐insensitivity of Clade I and their parent DREB III genes, Clade II evolved a further innovation in cold‐sensitive response and was stepwise expanded in eudicots and monocots by independent duplications. In geological time, the duplication events were mainly enriched around the Cretaceous–Paleogene (K–Pg) boundary and/or in the Late Cenozoic Ice Age, when the global average temperature significantly decreased. Consequently, the duplicated CBF/DREB1 genes contributed to the rewiring of CBFs/DREB1s‐regulatory network for cold tolerance. Altogether, our results highlight an origin and convergent evolution of CBFs/DREB1s and their regulatory network probably for angiosperms adaptation to global cooling.

The TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) family proteins are plant-specific transcription factors that have been well-acknowledged for designing the architectures of plant branch, shoot, and inflorescence. However, evidence for their innovation and emerging role in abiotic stress has been lacking. In this study, we identified a total of 36 TCP genes in Populus trichocarpa, 50% more than that in Arabidopsis (i.e., 24). Comparative intra-genomes showed that such significant innovation was mainly due to the most recent whole genome duplication (rWGD) in Populus lineage around Cretaceous-Paleogene (K-Pg) boundary after the divergence from Arabidopsis. Transcriptome analysis showed that the expressions of PtrTCP genes varied among leaf, stem, and root, and they could also be elaborately regulated by abiotic stresses (e.g., cold and salt). Moreover, co-expression network identified a cold-associated regulatory module including PtrTCP31, PtrTCP10, and PtrTCP36. Of them, PtrTCP10 was rWGD-duplicated from PtrTCP31 and evolved a strong capability of cold induction, which might suggest a neofunctionalization of PtrTCP genes and contribute to the adaptation of Populus lineage during the Cenozoic global cooling. Evidentially, overexpression of PtrTCP10 into Arabidopsis increased freezing tolerance and salt susceptibility. Integrating co-expression network and cis-regulatory element analysis confirmed that PtrTCP10 can regulate the well-known cold- and salt-relevant genes (e.g., ZAT10, GolS2, and SOS1), proving that PtrTCP10 is an evolutionary innovation in P. trichocarpa response to environmental changes. Altogether, our results provide evidence of the rWGD in P. trichocarpa responsible for the innovation of PtrTCP genes and their emerging roles in environmental stresses.

Angiosperms are one of the most diverse and abundant plant groups that are widely distributed on Earth, from tropical to temperate and polar zones. The wide distribution of angiosperms may be attributed to the evolution of sophisticated mechanisms of environmental adaptability, including cold tolerance. Since the development of high-throughput sequencing, transcriptome has been widely utilized to gain insights into the molecular mechanisms of plants in response to cold stress. However, previous studies generally focused on single or two species, and comparative transcriptome analyses for multispecies responding to cold stress were limited. In this study, we selected 11 representative angiosperm species, performed phylotranscriptome experiments at four time points before and after cold stress, and presented a profile of cold-induced transcriptome changes in angiosperms. Our multispecies cold-responsive RNA-seq datasets provide valuable references for exploring conserved and evolutionary mechanisms of angiosperms in adaptation to cold stress.