Sunflower NAC84 confers plant salt and drought tolerance and yield-increasing potential

Drought and salinity pose serious threats to global food security. However, enhancing crop stress tolerance through the overexpression of an individual gene often incurs trade-offs with other agronomic traits. Therefore, identifying alleles that simultaneously enhance stress tolerance and yield is a critical priority. Sunflower (Helianthus annuus L.) is often chosen for saline-alkali soil reclamation because of its significant salt and drought tolerance. As transcriptional controllers found only in plants, NAC proteins are central to orchestrating morphogenesis and mediating tolerance to various stresses. Here, we report that HaNAC84 confers salt and drought stress tolerance and exhibits yield-promoting potential. Stable over-expression of HaNAC84 in Arabidopsis and transient expression in sunflower both markedly increased tolerance to salt and drought. Mechanistically, HaNAC84 enhanced the activities of key antioxidant enzymes (SOD, POD, CAT, GR) and enhanced the overall antioxidant capacity, thereby limiting reactive oxygen accumulation and protecting membrane integrity. In Arabidopsis, HaNAC84 up-regulated POD, CAT and P5CS gene transcription, activated ABA biosynthesis and signaling to accelerate stomatal closure, and induced the expression of downstream defense genes (NHX1, DREB2A, LEA3, RD29A). Besides stress protection, HaNAC84 promoted root elongation and increased bolting branches, enhanced photosynthetic efficiency, and ultimately increased seed yield under control and stress conditions. Collectively, our findings identify HaNAC84 as a promising target for engineering stress-resilient crops that maintain productivity under abiotic stress.