Seed vigor is an important agronomic attribute, essentially associated with crop yield. High-temperature and humidity (HTH) stress directly affects seed development of plants, resulting in the decrease of seed vigor. Therefore, it is particularly important to discover HTH-tolerant genes related to seed vigor. Phenylalanine ammonia lyase (PAL, EC 4.3.1.24) is the first rate-limiting enzyme in the phenylpropanoid biosynthesis pathway and a key enzyme involved in plant growth and development and environmental adaptation. However, the biological function of PAL in seed vigor remains unknown. Here, GmPAL1.1 was cloned from soybean, and its protein was located in the cytoplasm and cell membrane. GmPAL1.1 was significantly induced by HTH stress in developing seeds. The overexpression of GmPAL1.1 in Arabidopsis (OE) accumulated lower level of ROS in the developing seeds and in the leaves than the WT at the physiological maturity stage under HTH stress, and the activities of SOD, POD, and CAT and flavonoid contents were significantly increased, while MDA production was markedly reduced in the leaves of the OE lines than in those of the WT. The germination rate and viability of mature seeds of the OE lines harvested after HTH stress were higher than those of the WT. Compared to the control, the overexpression of GmPAL1.1 in Arabidopsis enhanced the tolerance to salt and drought stresses during germination. Our results suggested the overexpression of GmPAL1.1 in Arabidopsis promoted seed vigor at the physiological maturation period under HTH stress and increased the seeds’ tolerance to salt and drought during germination.

Early spring low temperature hazards are a common problem in southern China's tobacco production areas, leading to slow germination of tobacco seeds. In the present study, spermine (Spm), salicylic acid (SA) and polyethylene glycol (PEG) were used to prime seeds of different tobacco cultivars. After priming, their germination indices were evaluated in an optimal temperature (25°C) germination test and a low temperature (12°C) germination test. In the optimal temperature germination experiment, priming with any of Spm, SA and PEG could improve the germination index (GI) and reduce the mean germination time (MGT) of 'Xiangyang No. 7' seeds. Moreover, priming with Spm or PEG enhanced the vigour indices (VI) at most priming concentrations and durations, while SA priming with 0.5 mmol L^-1 for 24 hours improved the germination potential (GE) and SA priming with 0.5 and 0.6 mmol L ^-1 for 48 hours improved germination potential (GP). For the low temperature germination experiment, Spm or PEG priming treatment based on the optimal temperature germination experiment markedly improved GI and VI, which was confirmed by the enhancement of antioxidative enzyme activities, while the selected SA priming treatments significantly enhanced GI except for at 0.6 mmol L^-1 for 12 hours. Our results indicated that Spm, SA and PEG could be used for enhancing chilling tolerance of tobacco seeds and improving seed germination.

Field high-temperature and high-humidity (HTH) stress causes soybean seed deterioration, including shrinkage, moldiness, browning, and reduced germination rate, thereby decreasing seed vigor, emergence performance, and commercial value. Clarifying the molecular mechanisms of seed vigor formation under HTH stress is critical for identifying key genes and improving spring soybean seed quality. Plant homeodomain (PHD) proteins are conserved zinc-finger transcription factors involved in chromatin remodeling and stress responses. GmPHD3, a soybean PHD family member, has only been studied via heterologous expression in Arabidopsis; its authentic function in soybean remains unclear. In this study, we functionally characterized GmPHD3 in soybean. GmPHD3 is a nuclear-localized transcription factor containing Alfin and PHD domains, and is evolutionarily conserved across legumes and other plant species. Expression analysis showed that GmPHD3 was strongly induced by HTH stress, with rapid induction at 6 h in the tolerant cultivar Xiangdou No. 3 but delayed induction at 48 h in the sensitive Ningzhen No. 1. The GmPHD3 promoter harbors abscisic acid (ABA) and stress-responsive elements, and GUS assays confirmed its response to ABA and HTH. Overexpression of GmPHD3 in soybean significantly enhanced seed vigor under artificial accelerated aging by increasing the germination speed and activities of SOD, POD, while reducing TBARS content. Meanwhile, GmPHD3 negatively regulated seed longitudinal elongation, leading to a short and round seed shape without changing single-seed weight. It also significantly decreased the proportion of palmitic acid, a major saturated fatty acid. These results demonstrate that GmPHD3 positively regulates soybean seed vigor and stress resistance under HTH stress by modulating the antioxidant system and modifying seed morphology and fatty acid composition, providing a valuable target for soybean molecular breeding.