Preliminary characterization of TaLTP3 function in abiotic stress responses and grain size regulation in rice

Lipid transfer proteins (LTPs) are small molecules capable of binding and transporting lipids. However, the functions of wheat TaLTPs genes remain largely unexplored. In our preliminary study on TaSnRK2.4, TaLTP3 was identified as a candidate interacting protein. This study analyzed the expression of TaLTP3 in various wheat tissues during the jointing, flowering, and heading stages. TaLTP3 was found to be expressed in all tested tissues, with higher expression levels in shoots than in roots. Analysis of TaLTP3 expression patterns under abiotic stresses revealed that ABA, MeJA, low temperature, and heat treatments induced its expression in both leaves and roots at the seedling stage. To investigate its biological roles, TaLTP3 was overexpressed in rice. Although TaLTP3- overexpression had no significant effect on plant height or root number, it significantly increased panicle branches and grain number, but significantly reduced the grain size and thousand grain weight, ultimately leading to a decrease in yield. Sequence analysis revealed that TaLTP3s were highly conserved among subgenomes, with only one polymorphic site located in the intron of the B-subgenome copy, the remaining polymorphic sites were found in promoter and intron regions. Notably, a polymorphic site in promoter region of the B-subgenome copy was located within DRE core cis-acting element, suggesting a potential role in drought stress response. These results suggest that TaLTP3 participates in drought stress responses via DRE-mediated promoter regulation and uncover a previously unrecognized role for TaLTP3 in governing yield-related traits. This study provides a strategic direction for investigating the molecular mechanisms of drought response and molecular design breeding.