MicroRNAs balance growth and salt stress responses in sweet sorghum.

Salt stress is one of the major causes of reduced crop production, limiting agricultural development globally. Plants have evolved with complex systems to maintain the balance between growth and stress responses, where signaling pathways such as hormone signaling play key roles. Recent studies revealed that hormones are modulated by microRNAs (miRNAs). Previously, two sweet sorghum (Sorghum bicolor) inbred lines with different salt tolerance were identified: the salt-tolerant M-81E and the salt-sensitive Roma. The levels of endogenous hormones in M-81E and Roma varied differently under salt stress, showing a different balance between growth and stress responses. miRNA and degradome sequencing showed that the expression of many upstream transcription factors regulating signal transduction and hormone-responsive genes was directly induced by differentially expressed miRNAs, whose levels were very different between the two sweet sorghum lines. Furthermore, the effects of representative miRNAs on salt tolerance in sorghum were verified through a transformation system mediated by Agrobacterium rhizogenes. Also, miR-6225-5p reduced the level of Ca2+ in the miR-6225-5p-overexpressing line by inhibiting the expression of the Ca2+ uptake gene SbGLR3.1 in the root epidermis and affected salt tolerance in sorghum. This study provides evidence for miRNA-mediated growth and stress responses in sweet sorghum.

Identification of the MYB gene family in Sorghum bicolor and functional analysis of SbMYBAS1 in response to salt stress.

Salt stress adversely affects plant growth and development. It is necessary to understand the underlying salt response mechanism to improve salt tolerance in plants. MYB transcription factors can regulate plant responses to salt stress. However, only a few studies have explored the role of MYB TFs in Sorghum bicolor (L.) Moench. So we decided to make a systematic analysis and research on the sorghum MYB family. A total of 210 MYB genes in sorghum were identified in this study. Furthermore, 210 MYB genes were distributed across ten chromosomes, named SbMYB1-SbMYB210. To study the phylogeny of the identified TFs, 210 MYB genes were divided into six subfamilies. We further demonstrated that SbMYB genes have evolved under strong purifying selection. SbMYBAS1 (SbMYB119) was chosen as the study object, which the expression decreased under salt stress conditions. Further study of the SbMYBAS1 showed that SbMYBAS1 is located in the nucleus. Under salt stress conditions, Arabidopsis plants overexpressed SbMYBAS1 showed significantly lower dry/fresh weight and chlorophyll content but significantly higher membrane permeability, MDA content, and Na+/K+ ratio than the wild-type Arabidopsis plants. Yeast two-hybrid screening result showed that SbMYBAS1 might interact with proteins encoded by SORBI_302G184600, SORBI_3009G247900 and SORBI_3004G59600. Results also showed that SbMYBAS1 could regulate the expression of AtGSTU17, AtGSTU16, AtP5CS2, AtUGT88A1, AtUGT85A2, AtOPR2 and AtPCR2 under salt stress conditions. This work laid a foundation for the study of the response mechanism of sorghum MYB gene family to salt stress.

R2R3 MYB transcription factor SbMYBHv33 negatively regulates sorghum biomass accumulation and salt tolerance.

KEY MESSAGE: SbMYBHv33 negatively regulated biomass accumulation and salt tolerance in sorghum and Arabidopsis by regulating reactive oxygen species accumulation and ion levels. Salt stress is one of the main types of environmental stress leading to a reduction in crop yield worldwide. Plants have also evolved a variety of corresponding regulatory pathways to resist environmental stress damage. This study aimed to identify a SbMYBHv33 transcription factor that downregulates in salt, drought, and abscisic acid (ABA) in the salt-tolerant inbred line sorghum M-81E. The findings revealed that overexpression of SbMYBHv33 in sorghum significantly reduced sorghum biomass accumulation at the seedling stage and also salinity tolerance. Meanwhile, a heterologous transformation of Arabidopsis with SbMYBHv33 produced a similar phenotype. The loss of function of the Arabidopsis homolog of SbMYBHv33 resulted in longer roots and increased salt tolerance. Under normal conditions, SbMYBHV33 overexpression promoted the expression of ABA pathway genes in sorghum and inhibited growth. Under salt stress conditions, the gene expression of SbMYBHV33 decreased in the overexpressed lines, and the promotion of these genes in the ABA pathway was attenuated. This might be an important reason for the difference in growth and stress resistance between SbMYBHv33-overexpressed sorghum and ectopic expression Arabidopsis. Hence, SbMYBHv33 is an important component of sorghum growth and development and the regulation of salt stress response, and it could negatively regulate salt tolerance and biomass accumulation in sorghum.

Sorghum: A Multipurpose Crop.

Sorghum (Sorghum bicolor L.) is one of the top five cereal crops in the world in terms of production and planting area and is widely grown in areas with severe abiotic stresses such as drought and saline-alkali land due to its excellent stress resistance. Moreover, sorghum is a rare multipurpose crop that can be classified into grain sorghum, energy sorghum, and silage sorghum according to its domestication direction and utilization traits, endowing it with broad breeding and economic value. In this review, we mainly discuss the latest research progress and regulatory genes of agronomic traits of sorghum as a grain, energy, and silage crop, as well as the future improvement direction of multipurpose sorghum. We also emphasize the feasibility of cultivating multipurpose sorghum through genetic engineering methods by exploring potential targets using wild sorghum germplasm and genetic resources, as well as genomic resources.