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Background: The auxin indole-3-acetic acid (IAA) is a type of endogenous plant hormone with a low concentration in plants, but it plays an important role in their growth and development. The AUX/IAA gene family was found to be an early sensitive auxin gene with a complicated way of regulating growth and development in plants. The regulation of root growth and development by AUX/IAA family genes has been reported in Arabidopsis, rice and maize., Results: In this study, subcellular localization indicated that ZmIAA1-ZmIAA6 primarily played a role in the nucleus. A thermogram analysis showed that AUX/IAA genes were highly expressed in the roots, which was also confirmed by the maize tissue expression patterns. In maize overexpressing ZmIAA5 , the length of the main root, the number of lateral roots, and the stalk height at the seedling stage were significantly increased compared with those of the wild type, while the EMS mutant zmiaa5 was significantly reduced. The total number of roots and the dry weight of maize overexpressing ZmIAA5 at the mature stage were also significantly increased compared with those of the wild type, while those of the mutant zmiaa5 was significantly reduced. Yeast one-hybrid experiments showed that ZmTCP15/16/17 could specifically bind to the ZmIAA5 promoter region. Bimolecular fluorescence complementation and yeast two-hybridization indicated an interaction between ZmIAA5 and ZmARF5., Conclusions: Taken together, the results of this study indicate that ZmIAA5 regulates maize root growth and development by interacting with ZmARF5 under the specific binding of ZmTCP15/16/17 ., Competing Interests: The authors declare there are no competing interests., (©2022 Yang et al.)

Highlights • ZmUBP15 , ZmUBP16 and ZmUBP19 are specifically in response to Cd and salt stress in maize. • ZmUBP15, ZmUBP16 and ZmUBP19 are conserved in maize and localized in cell membrane. • Over-expression of ZmUBP15 , ZmUBP16 or ZmUBP19 partially rescue ub p16 -1 tolerance to Cd and salt stress in Arabidopsis. • Over-expression of ZmUBP15 , ZmUBP16 or ZmUBP19 enhance Arabidopsis tolerance to Cd stress and salt stress. Abstract Ubiquitin-Specific Protease16 (UBP16) has been described involved in cadmium stress and salt stress in Arabidopsis , however nothing is known about the functions of its homologs in maize. In this study, we investigate the functions of ZmUBP15 , ZmUBP16 and ZmUBP19 , three Arabidopsis UBP16 homologs in maize. Our results indicate that ZmUBP15 , ZmUBP16 and ZmUBP19 are ubiquitously expressed throughout plant development, and ZmUBP15, ZmUBP16 and ZmUBP19 proteins are mainly localized in plasma membrane. Complementation analyses show that over-expression of ZmUBP15 or ZmUBP16 can rescue the defective phenotype of ub p16 -1 in cadmium stress. In addition, over-expression of ZmUBP15 , ZmUBP16 or ZmUBP19 can increase the plant tolerance to cadmium stress. These results indicate that ZmUBP15 , ZmUBP16 and ZmUBP19 are required for plant to tolerance the cadmium stress. Consistent with this point, cadmium-related genes are markedly up-regulated in seedlings over-expressing ZmUBP15 , ZmUBP16 or ZmUBP19. Furthermore, our data indicate that ZmUBP15 , ZmUBP16 and ZmUBP19 partially rescue the salt-stress phenotype of ub p16 -1. Thus, our research uncover the functions of three novel maize proteins, ZmUBP15, ZmUBP16 and ZmUBP19, which are required for plants in response to cadmium stress and salt stress. [ABSTRACT FROM AUTHOR]