Guangyang Wang

Summary: Ca ²⁺ signals play a crucial role in heat stress (HS) resistance. However, how Ca ²⁺ signals are decoded and regulate the downstream targets of HS signaling remains unclear in plants. Cool‐season grasses are sensitive to high‐temperature conditions and should evolve distinctive heat stress response mechanisms. Here, we identified the calcium‐dependent protein kinase 19 (FaCPK19), which decoded the unique Ca ²⁺ signal triggered by HS in cool‐season grass tall fescue ( Festuca arundinacea Schreb.). The FaCPK19 was activated upon HS and positively regulated thermotolerance in tall fescue. FaCPK19 interacted with the thermo‐tolerance 1 ( FaTT1 ), which encodes an α2 subunit of the 26S proteasome, and phosphorylated its Thr172 (T172) residue. Under HS, overexpressing FaTT1 ^T172A ( FaTT1 ^T172A ‐OE , phospho‐deficient) grasses resulted in significantly lower 20S and 26S proteasome activity and reduced expression of downstream HS‐responsive genes compared to gain‐function transgenic grasses ( FaTT1‐OE ). The Facpk19 mutant was weakened in 20S and 26S proteasome activity under HS. Loss of T172 phosphorylation in FaTT1 ^T172A ‐OE showed a weakened heat‐tolerance phenotype than FaTT1‐OE. T172 residue at TT1 is evolutionarily conserved from plants to animals, indicating it could be widely used for thermotolerance breeding in grasses and crops. Our findings reveal a Ca ²⁺ ‐FaCPK19–FaTT1 axis by which an HS‐induced Ca ²⁺ signal is decoded with enhanced thermotolerance in tall fescue.

Bermudagrass is one of the most extensively used warm‐season grasses. It is widely used in landscaping, stadium construction and soil remediation due to its excellent regeneration, trampling and stress tolerances. However, studies on its regulatory mechanism and variety improvement by genetic engineering are still at a standstill, owing to its genetic variability and intrinsic limits linked with some resistance to Agrobacterium infection. In this study, we established a higher efficient Agrobacterium‐mediated transformation via screening for vital embryogenic callus and improving infection efficiency. The superior callus was light yellow, hard granular and compact, determined with a differentiation rate of more than 95%. The optimized infestation courses by gentle shaking, vacuuming and sonicating were used. The infested calluses were co‐cultured for 3 days, followed by desiccation treatments for 1 day to get higher infection efficiency. Then the CdHEMA1 gene, essential for chlorophyll biosynthesis, was cloned and transferred into bermudagrass to validate the aforementioned optimization procedures integrally. Molecular‐level analyses indicated that the CdHEMA1 gene had successfully integrated and was greatly increased in transgenic seedlings. Results of the photosynthetic capacity assessment showed that CdHEMA1 overexpression may considerably enhance the contents of photosynthetic pigments, OJIP curve and reaction center density (RC/CSo) to absorb (ABS/CSo, ABS/CSM) and capture (TRo/CSo) more light energy, hence improve the performance indices PI_ABS and PI_CS compared to the wild type. The successful completion of this project would provide a solid platform for further gene function study and molecular breeding of bermudagrass.