Coordination of drought-adaptive root growth plasticity through auxin homeostasis by the ZmSPL12-ZmYUC5 module in...

Climate change-induced drought increasingly threatens global maize production. Drought-adaptive root plasticity in maize depends on auxin signaling, yet how auxin homeostasis is dynamically tuned in response to water deficit remains unclear. This study investigates the transcription factor SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 12 (ZmSPL12) as a context-dependent modulator of root growth plasticity under drought stress (DS). We combined phenotypic phenotyping of transgenic overexpression and knockout maize lines, molecular biochemical assays, DAP-seq, hormone quantification, and field drought trials of inbred lines and commercial hybrids. ZmSPL12 overexpression produces shorter roots under well-watered conditions yet sustains root elongation under DS, conferring enhanced drought adaptation. ZmSPL12 directly binds to the promoter of the auxin biosynthesis gene ZmYUC5 and suppresses its expression, establishing a buffered basal auxin state in root tips, preventing drought-triggered auxin overaccumulation that inhibits meristem activity. Field trials show that ZmSPL12 overexpression enhances drought resilience in inbred lines and improves grain yield stability in commercial hybrids under water-limited conditions. The ZmSPL12-ZmYUC5 module acts as a molecular rheostat that fine-tunes root-tip auxin homeostasis to coordinate drought-adaptive root architectural plasticity in maize. This work reveals a conditional-plasticity regulatory mechanism and offers a valuable genetic resource for breeding climate-resilient crops.