Abstract: [Objective] Ca²⁺-dependent-deoxyribonuclease (CDD) can degrade ssDNA and dsDNA,however it is unclear that the function in response to drought and severe salt stresses.In this study,the role of CDD in growth and development of poplar trees (Populus alba×P.glandulosa ‘84K’) and the possible molecular mechanism in response to drought and salt stresses were analyzed,in order to provide a foundation for the elucidation of the regulatory role of CDD in stress tolerance of poplars.[Method] PtoCDD overexpressed and PagCDD knockout poplar lines (cuttings from tissue-cultured plants) were treated in drought and severe salt stresses and the phenotypes were accessed,including growth and adventitious rooting (AR).The anatomy of stem sections of transgenic lines and control plants (84K) were performed and the layers of xylem cells were compared.The expression of PIP in CDD transgenic poplar lines in response to drought and salt stresses were also analyzed by qRT-PCR.[Result] There were no significant differences between the transgenic poplar lines and the non-transgenic 84K in normal condition,while CDD knockout plants and CDD overexpressed plants respectively exhibited significantly higher and shorter than the control plants under the drought and salt stresses.This analysis indicated that CDD overexpression enhanced the sensitivity of poplars to the stresses.The anatomy analysis revealed that the layers of xylem cells were in the sequence of CDD overexpression lines > control 84K > CDD knockout lines from thick to thin in normal condition,while CDD knockout lines > control 84K > CDD overexpression lines under the stresses.The anatomy analysis demonstrated that the involvement of CDD in xylem differentiation was significantly affected by the stresses.In addition,the number of ARs exhibited CDD knockout lines > control 84K > CDD overexpression lines in the sequence from high to low,thus the CDD expression level could alter the number of ARs thus change the sensitivity of poplars in response to the stresses.qRT-PCR analysis showed that the expression of certain PIPs involved in responding to the the stresses were up-regulated in overexpression lines.This study demonstrated that CDD could induce the expression of certain PIP members to alter water usage.[Conclusion] Overexpression and knockout CDD could alter the expression of PIP,water usage,and the number of AR,of transgenic poplars,leading to the change in growth and development and the display of different sensitivity under the drought and salt stresses.Therefore,CDD is involved in the process of responding to the drought and salt stresses in poplars.

Key words: CDD, Populus alba×P, glandulosa ‘84K’, drought stress, salt stress, xylem, adventitious root