Plant protease inhibitors are a ubiquitous feature of plant species and exert a substantial influence on plant stress responses. However, the KTI (Kunitz trypsin inhibitor) family responding to abiotic stress has not been fully characterized in Populus yunnanensis. In this study, we conducted a genome-wide study of the KTI family and analyzed their gene structure, gene duplication, conserved motifs, cis-acting elements, and response to stress treatment. A total of 29 KTIs were identified in the P. yunnanensis genome. Based on phylogenetic analysis, the PyKTIs were divided into four groups (1,2, 3, and 4). Promoter sequence analysis showed that the PyKTIs contain many cis-acting elements related to light, plant growth, hormone, and stress responses, indicating that PyKTIs are widely involved in various biological regulatory processes. RNA sequencing and real-time quantitative polymerase chain reaction analysis showed that KTI genes were differentially expressed under the inverted cutting stress of P. yunnanensis. Transcriptome analysis of P. yunnanensis leaves revealed that PyKTI16, PyKTI18, and PyKTI19 were highly upregulated after inverted cutting. Through the GEO query of Populus transcriptome data, KTI genes played a positive defense role in MeJa, drought, time series, and pathogen stress. This study provided comprehensive information for the KTI family in P. yunnanensis, which should be helpful for the functional characterization of P. yunnanensis KTI genes in the future.

Populus qamdoensis cuttings were treated with transparent colorless film (WF), blue film (BF), and green film (GF), and the leaf physiological indices were measured and transcriptome sequencing was performed. The results showed that BF treatment significantly inhibited the height growth, leaf length, and leaf width of P. qamdoensis, while significantly increasing the thickness of leaf palisade tissue, upper epidermis, and the density of leaf structure. The GF treatment increased stomatal conductance (Gs) and intercellular CO₂ concentration (Ci), while the BF treatment enhanced water use efficiency (WUE). Both BF and GF increased the contents of chlorophyll b (Chl b) and carotenoids (Car). BF treatment increased the content of total soluble sugars but decreased the contents of sucrose and starch. Transcriptome analysis revealed that under BF treatment, most genes in the sucrose and starch metabolism pathways were up-regulated, and the AUX/IAA, GH3, and SAUR genes in the auxin pathway also showed an up-regulated trend. In contrast, under GF treatment, most genes in the porphyrin and chlorophyll metabolic pathway were up-regulated, and most genes in the gibberellin pathway also showed up-regulation. Analysis of photoreceptor gene expression showed that GF treatment significantly up-regulated the expression of HYH, COP1, CRY1, HY5, and PIF4 genes, while BF treatment had the opposite effect. These results provide a theoretical basis for revealing the evolutionary mechanisms underlying the adaptation of plants to different light environments.