Regulation of cytokinin biosynthesis using PtRD26<sub>pro</sub>‐IPT module improves drought tolerance through PtARR10‐PtYUC4/5‐mediated reactive oxygen species removal in<i>Populus</i>
Hou‐Ling Wang, Qi Yang, Shuya Tan, Ting Wang, Yi Zhang, Yanli Yang, Weilun Yin, Xinli Xia, Hongwei Guo, Zhonghai Li
Abstract
Abstract Drought is a critical environmental factor which constrains plant survival and growth. Genetic engineering provides a credible strategy to improve drought tolerance of plants. Here, we generated transgenic poplar lines expressing the isopentenyl transferase gene ( IPT ) under the driver of PtRD26 promoter ( PtRD26 pro ‐IPT ). PtRD26 is a senescence and drought‐inducible NAC transcription factor. PtRD26 pro ‐IPT plants displayed multiple phenotypes, including improved growth and drought tolerance. Transcriptome analysis revealed that auxin biosynthesis pathway was activated in the PtRD26 pro ‐IPT plants, leading to an increase in auxin contents. Biochemical analysis revealed that ARABIDOPSIS RESPONSE REGULATOR10 ( PtARR10 ), one of the type‐B ARR transcription factors in the cytokinin pathway, was induced in PtRD26 pro ‐IPT plants and directly regulated the transcripts of YUCCA4 ( PtYUC4 ) and YUCCA5 ( PtYUC5 ), two enzymes in the auxin biosynthesis pathway. Overexpression of PtYUC4 enhanced drought tolerance, while simultaneous silencing of PtYUC4/5 evidently attenuated the drought tolerance of PtRD26 pro ‐IPT plants. Intriguingly, PtYUC4/5 displayed a conserved thioredoxin reductase activity that is required for drought tolerance by deterring reactive oxygen species accumulation. Our work reveals the molecular basis of cytokinin and auxin interactions in response to environmental stresses, and shed light on the improvement of drought tolerance without a growth penalty in trees by molecular breeding.