AUTHOR=Al-Mamun Mahamud Hossain , Cazzonelli Christopher Ian , Krishna Priti 

TITLE=BZR1 and BES1 transcription factors mediate brassinosteroid control over root system architecture in response to nitrogen availability

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1387321

DOI=10.3389/fpls.2024.1387321

ISSN=1664-462X

ABSTRACT=<p>Plants modify their root system architecture (RSA) in response to nitrogen (N) deficiency. The plant steroidal hormone, brassinosteroid (BR), plays important roles in root growth and development. This study demonstrates that optimal levels of exogenous BR impact significant increases in lateral root length and numbers in <italic>Arabidopsis</italic> seedlings under mild N-deficient conditions as compared to untreated seedlings. The impact of BR on RSA was stronger under mild N deficiency than under N-sufficient conditions. The BR effects on RSA were mimicked in dominant mutants of BZR1 and BES1 (<italic>bzr1-1D</italic> and <italic>bes1-D</italic>) transcription factors, while the RSA was highly reduced in the BR-insensitive mutant <italic>bri1-6</italic>, confirming that BR signaling is essential for the development of RSA under both N-sufficient and N-deficient conditions. Exogenous BR and constitutive activity of BZR1 and BES1 in dominant mutants led to enhanced root meristem, meristematic cell number, and cortical cell length. Under mild N deficiency, <italic>bzr1-1D</italic> displayed higher fresh and dry shoot weights, chlorophyll content, and N levels in the shoot, as compared to the wild type. These results indicate that BR modulates RSA under both N-sufficient and N-deficient conditions via the transcription factors BES1/BZR1 module and confers tolerance to N deficiency.</p>