Soybean ( Glycine max [L.] Merr.) has been grown in diverse environments in a wide range of latitudes in the world. However, the adaptation of soybean to low-latitude, high-altitude environments characterized by short day and low temperature is still in its early stages. To understand the genetic basis of adaptation in this region, we conducted cultivar screening in low-latitude, high-altitude mountainous regions and carried out genome-wide association studies (GWAS) using 200 diverse soybean cultivars spanning maturity groups 000 to VIII. Evaluation of flowering time (DTF), maturity time (DTM), and other agronomic traits including node number on main stem (NNM), plant height (PH), effective number of pods per plant (EPN) and 100-seed weight (HGW) were performed in Bamei with the altitude of 3460 m (30°29’4”N and 101°28’50”E) and Xianshui with the altitude of 2946 m (30°57’48”N and 101°9’26”E), in Daofu county, Sichuan province, southwest China, in 2019 and 2023, respectively. We screened 5 MG I-II adapted cultivars for Bamei and 17 MG II-V cultivars, for Xianshui, exhibiting late flowering and maturity, along with tall plant height, and high number of nodes and pods per plant. The allelic combinations E1/e2-ns/e3-tr/E4 and E1/e2-ns/E3/E4, and only E1/e2-ns/E3/E4 predominated in the adaptive cultivars in Bamei and Xianshui, respectively. Thus, the cultivars adaptive to low-latitude and high-altitude regions are featured with relatively late flowering and maturing in MG I-V mostly from mid- and low-latitude region with allelic combination mostly of E1/e2-ns/E3/E4. Additionally, our results revealed 9, 6, and 2 genomic regions significantly associated with DTF, NNM and PH, respectively, with two of these genomic regions having QTNs significantly associated with both DTF and PH. Most significant QTNs of the genomic regions associated with DTF were located near previously identified quantitative trait loci, and their alternative loci caused significant differences in flowering time. Furthermore, 7 genomic regions were located near homologs of Arabidopsis flowering time genes FD-1, bZIP29, SEC, PA2, PIE1, FY, IAA31, AS1 and MBD9. Non-synonymous mutations within the candidate genes Glyma.09g112200 ( GmPIE1) , Glyma.13g198200 ( GmFY) and Glyma.17g042800 ( GmIAA31) were found to cause later flowering and taller plant height in both environments. Collection of adaptive cultivars, molecular markers, and candidate genes identified in this study holds substantial promise within the realm of soybean adaptation in low-latitude and high-altitude regions.

Photosynthetic compensation is an effective strategy for optimizing light energy utilization in heterogeneous light (HL). However, it is often impaired, and the involving mechanisms remain unclear, particularly in C 4 plants. When maize ( Zea mays L.) cultivars with different photosynthetic compensation capability were exposed to HL, P n of shaded leaves (S-leaves) decreased in both cultivars, while the P n of unshaded leaves (US-leaves) increased in RY1210(RY) and decreased in ZD808(ZD). Results also showed increased SPS level, decreased AGPase level, and reduced Trehalose-6-phosphate (Tre6P) content in US-leaves of both cultivars, indicating enhanced flux from triose phosphate (TP) to sucrose synthesis under HL. In addition, SUTs and SWEETs levels of US-leaves increased in RY, while they decreased in ZD. This result implies that the sucrose export from the US-leaves of plants with photosynthetic compensation was enhanced. In US-leaves of ZD, restricted sucrose export led to increased sucrose and starch, accompanied by a substantial rise in TST2/ SUT2 and extensive accumulation of sucrose in vacuoles. In summary, photosynthetic compensation involves enhanced flux from TP to sucrose synthesis and increased sucrose export in US-leaves. In this process, Tre6P may function as a systemic signal modulator, regulating sucrose synthesis in source leaves and phloem loading. The increased sucrose storage in vacuoles may delay the Tre6P perception of sucrose levels induced by HL, which ensures the increased flux of sucrose synthesis.

As an essential regulator of photosynthesis and hormone signaling, light plays a critical role in leaf senescence and yield gain in crops. Previously, numerous studies have shown that the narrow-wide-row planting pattern, especially under intercropping systems, is more beneficial for crops to enhance light interception, energy conversion, and yield improvement. However, the narrow-wide-row planting pattern inevitably leads to a heterogeneous light environment for crops (i. e., maize in maize-based intercropping systems) on both sides of the plant. The mechanism by which it affects leaf senescence and yield of maize under a narrow-wide-row planting pattern is still unclear. Therefore, in this study, we compared the leaf senescence and yield formation process of maize under homogeneous (normal light, NL and full shade, FS) and heterogeneous (partial light, PL) light conditions. Results revealed that partial light treatment influenced the homeostasis of growth and senescence hormones by regulating the expression of ZmPHYA and ZmPIF5. Compared to normal light and full shade treatments, partial light delayed leaf senescence by 3.6 and 5.9 days with 2.2 and 3.3 more green leaves and 1.1 and 1.4 fold nitrogen uptake, respectively. Partial light reduced oxidative stress by enhancing antioxidant enzyme activities of PS (shade side of partial light) leaves, which improved photosynthetic assimilation, balanced sucrose, and starch ultimately maintaining the similar maize yield to NL. Overall, these results are important for understanding the mechanism of leaf senescence in maize, especially under heterogeneous light environments, which maize experienced in maize-based intercropping systems. Furthermore, these findings are providing proof of getting a high yield of maize with less land in intercropping systems. Thus, we can conclude that maize-based intercropping systems can be used for obtaining high maize yields maintained under the current climate change scenario.

Mildew severely reduces soybean yield and quality, and pods are the first line of defense against pathogens. Maize-soybean intercropping (MSI) reduces mildew incidence on soybean pods; however, the reason remains unclear. Previous studies confirmed the key function of soy isoflavone in soybean mildew resistance, while changing light (CL) from maize shading is the most important environmental feature in MSI. CL also regulates isoflavone biosynthesis in soybean seeds. We hypothesized that CL affects isoflavone accumulation in soybean pods, impacting their disease resistance. In the present study, shading treatments were applied during different developmental stages of soybean plants according to various CL environments under MSI. Chlorophyll fluorescence imaging (CFI) and classical evaluation methods confirmed that CL, especially vegetative stage shading (VS), enhances pod resistance to mildew. Further metabolomic analyses and exogenous inhibitor experiments revealed the important relationship between jasmonic acid (JA) and isoflavone biosynthesis, which has a synergistic effect on the enhanced resistance of CL-treated pods to mildew. VS promoted the biosynthesis and accumulation of constitutive isoflavones upstream of the isoflavone pathway, such as aglycones and glycosides, in soybean pods. When mildew infects pods, endogenous JA signaling stimulates the biosynthesis of downstream inducible malonylated isoflavones and glyceolin to improve pod resistance.

Maize shading affects the growth and development of soybean in maize soybean intercropping systems. Two different soybean varieties were (ND12, high shade-tolerant, and GX3, low shade-tolerant) relay intercrop with maize in different (T1, double row, and T2, single row) relay strip intercropping systems, and the results of the both planting arrangements of strip intercropping system were compared with the sole planting system of soybean. The results showed that shading reduced the content of photosynthetic pigment per unit area of soybean leaf, Fv/Fm, ΦPSⅡ, and Fv/Fo of ND12 and GX3 under T1 and T2. Moreover, T1 and T2 also decreased the density and size of stomata, leaf thickness, palisade tissue thickness of the tissue, and the size of the chloroplast and starch grains, while increased the thickness of the granum lamellae in both varieties of soybean. Nevertheless, the leaf area, aboveground biomass, photosynthetic capacity, photosynthetic organs measured morphological and architectural indices were found maximum in ND12 compared to GX3 in all planting patterns.