Conservation genomic investigation of an endangered conifer,Thuja sutchuenensis,reveals low genetic diversity but also low genetic load

Endangered species generally have small populations with low genetic diversity and a high genetic load.Thuja sutchuenensis is an endangered conifer endemic to southwestern China.It was once considered extinct in the wild,but in 1999 was rediscovered.However,little is known about its genetic load.We collected 67 individuals from five wild,isolated T.sutchuenensis populations,and used 636,151 SNPs to analyze the level of genetic diversity and genetic load in T.sutchuenensis to delineate the conservation units of T.sutchuenensis,based on whole transcriptome sequencing data,as well as target capture sequencing data.We found that populations of T.sutchuenensis could be divided into three groups.These groups had low levels genetic diversity and were moderately genetically differentiated.Our findings also indicate that T.sutchuenensis suffered two severe bottlenecks around the Last Glaciation Period and Last Glacial Maximum.Among Thuja species,T.sutchuenensis presented the lowest genetic load and hence might have purged deleterious mutations efficiently through purifying selection.However,distribution of fitness effects analysis indicated a high extinction risk for T.sutchuenensis.Multiple lines of evidence identified three management units for T.sutchuenensis.Although T.sutchuenensis possesses a low genetic load,low genetic diversity,suboptimal fitness,and anthropogenic pressures all present an extinction risk for this rare conifer.This might also hold true for many endangered plant species in the mountains all over the world.

Across two phylogeographic breaks: Quaternary evolutionary history of a mountain aspen (Populus rotundifolia) in the Hengduan Mountains

Biogeographical barriers to gene flow are central to plant phylogeography.In East Asia,plant distribution is greatly influenced by two phylogeographic breaks,the Mekong-Salween Divide and Tanaka-Kaiyong Line,however,few studies have investigated how these barriers affect the genetic diversity of species that are distributed across both.Here we used 14 microsatellite loci and four chloroplast DNA fragments to examine genetic diversity and distribution patterns of 49 populations of Populus rotundifolia,a species that spans both the Mekong-Salween Divide and the Tanaka-Kaiyong Line in southwestern China.Demographic and migration hypotheses were tested using coalescent-based approaches.Limited historical gene flow was observed between the western and eastern groups of P.rotundifolia,but substantial flow occurred across both the Mekong-Salween Divide and Tanaka-Kaiyong Line,manifesting in clear admixture and high genetic diversity in the central group.Wind-borne pollen and seeds may have facilitated the dispersal of P.rotundifolia following prevalent northwest winds in the spring.We also found that the Hengduan Mountains,where multiple genetic barriers were detected,acted on the whole as a barrier between the western and eastern groups of P.rotundifolia.Ecological niche modeling suggested that P.rotundifolia has undergone range expansion since the last glacial maximum,and demographic reconstruction indicated an earlier population expansion around 600 Ka.The phylogeographic pattern of P.rotundifolia reflects the interplay of biological traits,wind patterns,barriers,niche differentiation,and Quaternary climate history.This study emphasizes the need for multiple lines of evidence in understanding the Quaternary evolution of plants in topographically complex areas.

ACBP4-WRKY70-RAP2.12 module positively regulates submergence-induced hypoxia response in Arabidopsis thaliana

ACYL-CoA-BINDING PROTEINs(ACBPs)play crucial regulatory roles during plant response to hypoxia,but their molecular mechanisms remain poorly understood.Our study reveals that ACBP4 serves as a positive regulator of the plant hypoxia response by interacting with WRKY70,influencing its nucleocytoplasmic shuttling in Arabidopsis thaliana.Furthermore,we demonstrate the direct binding of WRKY70 to the ACBP4 promoter,resulting in its upregulation and suggesting a positive feedback loop.Additionally,we pinpointed a phosphorylation site at Ser638 of ACBP4,which enhances submergence tolerance,potentially by facilitating WRKY70's nuclear shuttling.Surprisingly,a natural variation in this phosphorylation site of ACBP4 allowed A.thaliana to adapt to humid conditions during its historical demographic expansion.We further observed that both phosphorylated ACBP4 and oleoyl-Co A can impede the interaction between ACBP4 and WRKY70,thus promoting WRKY70's nuclear translocation.Finally,we found that the overexpression of orthologous Bna C5.ACBP4and Bna A7.WRKY70 in Brassica napus increases submergence tolerance,indicating their functional similarity across genera.In summary,our research not only sheds light on the functional significance of the ACBP4 gene in hypoxia response,but also underscores its potential utility in breeding flooding-tolerant oilseed rape varieties.