基于转录水平解析尾巨桉径向生长对种植密度的响应

Response of Stem Radial Growth of Eucalyptus urophylla×E.grandis to Planting Density Based on Transcriptome Analysis

[目的]挖掘和鉴定桉树中响应种植密度的木质部生成关键基因,阐释种植密度影响林木径向生长的分子机制。[方法]通过PacBio Iso-Seq和RNA-Seq联合分析,鉴定了在高、低2个种植密度水平下尾巨桉DH32-29主茎的差异表达转录本并利用qRT-PCR进行组织表达分析。[结果]分别获得45490条在主茎中表达的非冗余全长转录本和443条在木质部中差异表达的转录本,并鉴定出60条差异表达的调控因子编码基因。在低种植密度条件下,植株直径生长量显著增加;参与细胞分裂调控的PXL2及其互作基因CUL1和T15D22.7、参与次生壁调控的MYB46、C3H14同源基因和其下游基因CesAs、LACs均上调表达,这些基因很可能是种植密度影响主茎径向生长过程中负责调控细胞分裂和次生壁合成的重要成员;参与筛管发育的NAC86同源基因及参与形成层发育和木质部分化的抑制子PTL同源基因也上调表达,它们可能促进木质部生成,这与草本植物中的功能不同。组织表达分析结果显示:PXL2、CUL1、T15D22.7、NAC86和PTL在韧皮部和木质部中优势表达;MYB46、C3H14、CesA和LAC17在木质部中优势表达。[结论]本研究鉴定了一批参与种植密度响应的木质部生成候选基因,构建了种植密度影响尾巨桉径向生长的分子调控网络模型,研究结果为深入解析种植密度影响林木径向生长的分子机制奠定基础。

[Objective]To identify the key genes of secondary xylem development response to planting density for a well understanding of molecular mechanism of planting density affecting radial growth of eucalypts.[Method]By a combination of PacBio Iso-Seq and RNA-Seq analysis,the differentially expressed transcriptomes of xylem cells in Eucalyptus urophylla×E.grandis were identified under high and low planting densities.The tissues expression profiles of these key genes were analyzed via qRT-PCR.[Result]A total of 45490 non-redundant full-length transcripts and 443 transcripts differentially expressed in xylem cells were obtained under high and low planting densities,and 60 transcripts encoding regulatory factors were obtained.Under low planting density,the diameters of trees increased significantly.The PXL2 and its interactional genes CUL1,T15D22.7 related to cell division,the MYB46,C3H14 with their downstream genes CesAs and LACs related to secondary wall regulation were preferentially expressed in the xylem cells.These genes might play key roles in the regulation of diameter growth under different densities.In addition,the NAC86 homologous genes involved in sieve element development and the inhibitor PTL homologous genes with dual functions in cambial cell proliferation and xylem differentiation were also up-regulated.They could promote the xylem development,which were different from the functions in herbaceous plants.The results of tissue expression analysis showed that PXL2,CUL1,T15D22.7,NAC86 and PTL were predominantly expressed in phloem and xylem,whereas MYB46,C3H14,CesA and LAC17 were predominantly expressed in xylem.[Conclusion]In this study,the candidate genes of xylem development related to planting density are identified and a model of molecular regulatory network that how the planting density affects radial growth of E.urophylla×E.grandis is proposed,which will benefit the intensive study of the molecular mechanism under different planting densities affecting radial growth for trees.