Soybean GmMYB133 Inhibits Hypocotyl Elongation and Confers Salt Tolerance in Arabidopsis

Soybean hypocotyl elongation is regulated by a MYB33-SWEET11/21-GA2ox8c module involving long-distance sucrose transport

The length of hypocotyl affects the height of soybean and lodging resistance, thus determining the final grain yield. However, research on soybean hypocotyl length is scarce, and the regulatory mechanisms are not fully understood. Here, we identified a module controlling the transport of sucrose, where sucrose acts as a messenger moved from cotyledon to hypocotyl, regulating hypocotyl elongation. This module comprises four key genes, namely MYB33, SWEET11, SWEET21 and GA2ox8c in soybean. In cotyledon, MYB33 is responsive to sucrose and promotes the expression of SWEET11 and SWEET21, thereby facilitating sucrose transport from the cotyledon to the hypocotyl. Subsequently, sucrose transported from the cotyledon up-regulates the expression of GA2ox8c in the hypocotyl, which ultimately affects the length of the hypocotyl. During the domestication and improvement of soybean, an allele of MYB33 with enhanced abilities to promote SWEET11 and SWEET21 has gradually become enriched in landraces and cultivated varieties, SWEET11 and SWEET21 exhibit high conservation and have undergone a strong purified selection and GA2ox8c is under a strong artificial selection. Our findings identify a new molecular pathway in controlling soybean hypocotyl elongation and provide new insights into the molecular mechanism of sugar transport in soybean.

Soybean RVE8a confers salt and drought tolerance in Arabidopsis

Soybean is an economically important crop, which often suffers various abiotic stresses. REVEILLE (RVE) genes have been generally considered as circadian oscillators to mediate diverse developmental processes and plant response to environmental stresses. Addressing their roles is of significance for utilizing them to enhance agronomic traits in crops. However, our understanding of soybean RVEs is extremely limited. In the study, we investigated the expression patterns of soybean CCA1-like genes under salt stress using our RNA-Seq data. Subsequently, a salt stress-inducible gene, GmRVE8a, was chosen for further study. Phylogenetic analysis indicated that GmRVE8a is most closely related to Arabidopsis RVE4 and RVE8. Also, GmRVE8a showed circadian expression pattern with 24 h rhythmic period, suggesting that it might be a clock-regulated gene. Moreover, transgenic Arabidopsis lines over-expressing GmRVE8a were generated. It was observed that ectopic over-expression of GmRVE8a caused a significant delay in flowering. Further observation indicated that under salt and drought stress, transgenic seedlings were stronger than wild type. Consistently, three-week-old transgenic plants grew better than wild type under salt and drought conditions, and the MDA content in transgenic lines was significantly lower than wild type, suggesting that GmRVE8a might be a positive regulator in response to salt and drought stress. Intriguingly, Y2H assay indicated that GmRVE8a physically interacted with a drought-tolerant protein, GmNAC17. Overall, our findings provided preliminary information regarding the functional roles of GmRVE8a in response to salt and drought stress.

A novel miR160a-GmARF16-GmMYC2 module determines soybean salt tolerance and adaptation

Salt stress is a major challenge that has a negative impact on soybean growth and productivity. Therefore, it is important to understand the regulatory mechanism of salt response to ensure soybean yield under such conditions. In this study, we identified and characterized a miR160a-GmARF16-GmMYC2 module and its regulation during the salt-stress response in soybean. miR160a promotes salt tolerance by cleaving GmARF16 transcripts, members of the Auxin Response Factor (ARF) family, which negatively regulates salt tolerance. In turn, GmARF16 activates GmMYC2, encoding a bHLH transcription factor that reduces salinity tolerance by down-regulating proline biosynthesis. Genomic analysis among wild and cultivated soybean accessions identified four distinct GmARF16 haplotypes. Among them, the GmARF16H3 haplotype is preferentially enriched in localities with relatively saline soils, suggesting GmARF16H3 was artificially selected to improve salt tolerance. Our findings therefore provide insights into the molecular mechanisms underlying salt response in soybean and provide valuable genetic targets for the molecular breeding of salt tolerance.

Integrated analysis of transcriptomic and proteomic data reveals novel regulators of soybean (Glycine max) hypocotyl development

Hypocotyl elongation directly affects the seedling establishment and soil-breaking after germination. In soybean (Glycine max ), the molecular mechanisms regulating hypocotyl development remain largely elusive. To decipher the regulatory landscape, we conducted proteome and transcriptome analysis of soybean hypocotyl samples at different development stages. Our results showed that during hypocotyl development, many proteins were with extreme high translation efficiency (TE) and may act as regulators. These potential regulators include multiple peroxidases and cell wall reorganisation related enzymes. Peroxidases may produce ROS including H2 O2 . Interestingly, exogenous H2 O2 application promoted hypocotyl elongation, supporting peroxidases as regulators of hypocotyl development. However, a vast variety of proteins were shown to be with dramatically changed TE during hypocotyl development, including multiple phytochromes, plasma membrane intrinsic proteins (PIPs) and aspartic proteases. Their potential roles in hypocotyl development were confirmed by that ectopic expression of GmPHYA1 and GmPIP1-6 in Arabidopsis thaliana affected hypocotyl elongation. In addition, the promoters of these potential regulatory genes contain multiple light/gibberellin/auxin responsive elements, while the expression of some members in hypocotyls was significantly regulated by light and exogenous auxin/gibberellin. Overall, our results revealed multiple novel regulatory factors of soybean hypocotyl elongation. Further research on these regulators may lead to new approvals to improve soybean hypocotyl traits.

Twenty years of mining salt tolerance genes in soybean

Current combined challenges of rising food demand, climate change and farmland degradation exert enormous pressure on agricultural production. Worldwide soil salinization, in particular, necessitates the development of salt-tolerant crops. Soybean, being a globally important produce, has its genetic resources increasingly examined to facilitate crop improvement based on functional genomics. In response to the multifaceted physiological challenge that salt stress imposes, soybean has evolved an array of defences against salinity. These include maintaining cell homeostasis by ion transportation, osmoregulation, and restoring oxidative balance. Other adaptations include cell wall alterations, transcriptomic reprogramming, and efficient signal transduction for detecting and responding to salt stress. Here, we reviewed functionally verified genes that underly different salt tolerance mechanisms employed by soybean in the past two decades, and discussed the strategy in selecting salt tolerance genes for crop improvement. Future studies could adopt an integrated multi-omic approach in characterizing soybean salt tolerance adaptations and put our existing knowledge into practice via omic-assisted breeding and gene editing. This review serves as a guide and inspiration for crop developers in enhancing soybean tolerance against abiotic stresses, thereby fulfilling the role of science in solving real-life problems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01383-3.

Genome-wide identification of BBX gene family and their expression patterns under salt stress in soybean

BACKGROUND

BBX genes are key players in the regulation of various developmental processes and stress responses, which have been identified and functionally characterized in many plant species. However, our understanding of BBX family was greatly limited in soybean.

RESULTS

In this study, 59 BBX genes were identified and characterized in soybean, which can be phylogenetically classified into 5 groups. GmBBXs showed diverse gene structures and motif compositions among the groups and similar within each group. Noticeably, synteny analysis suggested that segmental duplication contributed to the expansion of GmBBX family. Moreover, our RNA-Seq data indicated that 59 GmBBXs showed different transcript profiling under salt stress, and qRT-PCR analysis confirmed their expression patterns. Among them, 22 GmBBXs were transcriptionally altered with more than two-fold changes by salt stress, supporting that GmBBXs play important roles in soybean tolerance to salt stress. Additionally, Computational assay suggested that GmBBXs might potentially interact with GmGI3, GmTOE1b, GmCOP1, GmCHI and GmCRY, while eight types of transcription factors showed potentials to bind the promoter regions of GmBBX genes.

CONCLUSIONS

Fifty-nine BBX genes were identified and characterized in soybean, and their expression patterns under salt stress and computational assays suggested their functional roles in response to salt stress. These findings will contribute to future research in regard to functions and regulatory mechanisms of soybean BBX genes in response to salt stress.