Rice, a staple food for nearly half of the world's population [1], is a thermophilic crop inherently sensitive to low temperatures due to its tropical and subtropical origin. Statistical data indicate that low temperatures have resulted in substantial damage to rice cultivation in 25 countries, including China, with affected areas exceeding 15 million hectares [2]. Rice may experience low-temperature stress at any stage of the crop cycle, from vegetative to reproductive growth. Chilling stress leads to reduced germination rate, seedling wilting, yellowing, or even death [3], [4]. At the seedling stage, exposure to daily average temperatures below 12 °C for four or more consecutive days typically causes irreversible damage to rice seedlings, significantly reducing yield and quality [5], [6]. Therefore, elucidating the complex regulatory mechanisms of chilling tolerance during seedling stage in rice, identifying cold resistant genes, and developing cold-tolerant varieties through molecular design breeding are crucial for ensuring global food security.

Multiple transcription factor families are involved in regulating the expression of plant genes responsive to chilling stress, including the WRKY, bHLH, and AP2/ERF families. Among these, the AP2/ERF family, particularly the CBF/DREB subfamily, plays a central and evolutionarily conserved role in cold adaptation [7], [8]. The function of CBF/DREBs is highly conserved across diverse species [9], [10]. OsDREB1A, OsDREB1B, and OsDREB1C have been shown to participate in cold stress response regulation in rice [11], [12], [13]. WRKY transcription factors also contribute broadly to cold signaling. For example, OsWRKY94 is activated by OsMADS57 under low temperature to balance growth and defense [14], whereas OsWRKY53 negatively regulates cold tolerance at the booting stage by repressing gibberellin biosynthesis [15]. Notably, OsWRKY76 acts as a positive regulator during seedling chilling stress. Under normal conditions, its expression is suppressed by OsWRKY63; upon cold exposure, OsWRKY76 is rapidly induced and interacts with OsbHLH148 to activate OsDREB1B, forming a coherent OsWRKY63-OsWRKY76-OsbHLH148-OsDREB1B regulatory cascade [16], [17]. Beyond transcriptional control, the stability of these regulators is often modulated post-translationally. In Arabidopsis, CBF protein turnover is tightly regulated via ubiquitin-mediated degradation involving 14–3-3 proteins, BTF3/L, and PP2CG1/2 [18], [19], [20]. Similarly, precise regulation of OsbHLH002/ICE1 is achieved through ubiquitination, SUMOylation, and phosphorylation [21], [22], [23], [24].

Programmed cell death 5 (PDCD5) is an evolutionarily conserved regulator of apoptosis across species. In humans, PDCD5 can function as a transcription factor or co-regulator and is known to modulate protein stability via the ubiquitin-proteasome system [25], [26], [27]. Its functional significance extends to plants. In Arabidopsis, AtPDCD5 is implicated in UV-B-induced DNA damage and dark-induced leaf senescence. Following UV-B exposure, AtPDCD5 transcription is enhanced; overexpression lines exhibit increased root cell death, while the pdcd5 mutant shows less damage and altered antioxidant mechanisms [28]. Conversely, reduced AtPDCD5 expression delays leaf senescence and is associated with higher chlorophyll levels [29]. In rice, studies by Jinshui Yang's team revealed that constitutive OsPDCD5 expression triggers PCD, leading to growth retardation, reduced fresh weight, decreased total protein content, and genomic DNA fragmentation [30]. Conversely, suppressing OsPDCD5 enhances tolerance to salt stress [31], and knockout lines significantly increase yield and improve plant architecture [32]. Furthermore, OsPDCD5 expression is induced by low temperature [31]. While these studies establish OsPDCD5 as a multifaceted regulator of PCD, hormone metabolism, stress resistance, and agronomic traits, its specific role in chilling tolerance remains unclear. In this study, we demonstrate that OsPDCD5 negatively regulates chilling tolerance at the seedling stage in rice. We further elucidate a novel molecular mechanism whereby OsPDCD5 interacts with and promotes the degradation of OsWRKY76, thereby disrupting the OsWRKY76-mediated transcriptional activation of OsDREB1B under chilling stress. These findings provide deeper insights into the function and molecular mechanisms of OsPDCD5, offering both theoretical foundations and practical guidance for breeding cold-tolerant, high-yielding rice varieties.