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Aluminum (Al) toxicity is a major factor limiting crop yields in acid soils. Sweet sorghum (Sorghum bicolor L.) is a high-efficient energy crop widely grown in tropical and subtropical regions of the world, where acid soil is common and Al toxicity is widespread. Here, we characterized a transcription factor SbHY5 in sweet sorghum, which mediated light to promote plant Al stress adaptation. The expression of SbHY5 was induced by Al stress and increasing light intensity. The overexpression of SbHY5 improved Al tolerance in transgenic plants, which was associated with increased citrate secretion and reduced Al content in roots. Meanwhile, SbHY5 was found to localize to the nucleus and displayed transcriptional activity. SbHY5 directly activated the expression of SbMATE, indicating that a HY5-MATE-dependent citrate secretion pathway is involved in Al tolerance in plants. SbSTOP1 was reported as a key transcription factor, regulating several Al tolerance genes. Here, inspiringly, we found that SbHY5 directly promoted the transcription of SbSTOP1, implying the existence of HY5-STOP1-Al tolerance genes-mediated regulatory pathways. Besides, SbHY5 positively regulated its own transcription. Our findings revealed a novel regulatory network in which a light signaling factor, SbHY5, confers Al tolerance in plants by modulating the expression of Al stress response genes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Masson SAS.)

Aluminum (Al) toxicity is a primary limiting factor for crop production in acidic soils. The WRKY transcription factors play important roles in regulating plant growth and stress resistance. In this study, we identified and characterized two WRKY transcription factors, SbWRKY22 and SbWRKY65, in sweet sorghum ( Sorghum bicolor L.). Al induced the transcription of SbWRKY22 and SbWRKY65 in the root apices of sweet sorghum. These two WRKY proteins were localized in the nucleus and exhibited transcriptional activity. SbWRKY22 showed the significant transcriptional regulation of SbMATE , SbGlu1 , SbSTAR1 , SbSTAR2a , and SbSTAR2b , which are major known Al tolerance genes in sorghum. Interestingly, SbWRKY65 had almost no effect on the aforementioned genes, but it significantly regulated the transcription of SbWRKY22 . Therefore, it is speculated that SbWRKY65 might indirectly regulate Al-tolerance genes mediated by SbWRKY22. The heterologous expression of SbWRKY22 and SbWRKY65 greatly improved the Al tolerance of transgenic plants. The enhanced Al tolerance phenotype of transgenic plants is associated with reduced callose deposition in their roots. These findings suggest the existence of SbWRKY22- and SbWRKY65-mediated Al tolerance regulation pathways in sweet sorghum. This study extends our understanding of the complex regulatory mechanisms of WRKY transcription factors in response to Al toxicity.

Cryptochromes are blue light receptors that regulate plant growth and development. They also act as the core components of the central clock oscillator in animals. Although plant cryptochromes have been reported to regulate the circadian clock in blue light, how they do so is unclear. Here we show that Arabidopsis cryptochrome 2 (CRY2) forms photobodies with the TCP22 transcription factor in response to blue light in plant cells. We provide evidence that PPK kinases influence the characteristics of these photobodies and that together these components, along with LWD transcriptional regulators, can positively regulate the expression of CCA1 encoding a central component of the circadian oscillator. Cryptochrome signaling has been reported to regulate circadian oscillations in plants. Here the authors show that CRY2 and the TCP22 transcription factors can form photobodies in a blue light dependent manner and induce expression of CCA1, a core component of the circadian oscillator. [ABSTRACT FROM AUTHOR]

Arabidopsis cryptochrome 2 (CRY2) and FLAVIN-BINDING, KELCH REPEAT, and F-BOX 1 (FKF1) are blue light receptors mediating light regulation of growth and development, such as photoperiodic flowering. CRY2 interacts with a basic helix–loop–helix transcription factor CIB1 in response to blue light to activate the transcription of the flowering integrator gene FLOWERING LOCUS T (FT). CIB1, CIB2, CIB4, and CIB5 function redundantly to promote flowering in a CRY2-dependent way and form various heterodimers to bind to the noncanonical E-box sequence in the FT promoter. However, the function of CIB3 has not been described. We discovered that CIB3 promotes photoperiodic flowering independently of CRY2. Moreover, CIB3 does not interact with CRY2 but interacts with CIB1 and functions synergistically with CIB1 to promote the transcription of the GI gene. FKF1 is required for CIB3 to promote flowering and enhances the CIB1–CIB3 interaction in response to blue light. [ABSTRACT FROM AUTHOR]

COP1/SPA1 complex in Arabidopsis inhibits photomorphogenesis through the ubiquitination of multiple photo-responsive transcription factors in darkness, but such inhibiting function of COP1/SPA1 complex would be suppressed by cryptochromes in blue light. Extensive studies have been conducted on these mechanisms in Arabidopsis whereas little attention has been focused on whether another branch of land plants bryophyte utilizes this blue-light regulatory pathway. To study this problem, we conducted a study in the liverwort Marchantia polymorpha and obtained a MpSPA knock-out mutant, in which Mpspa exhibits the phenotype of an increased percentage of individuals with asymmetrical thallus growth, similar to MpCRY knock-out mutant. We also verified interactions of MpSPA with MpCRY (in a blue light-independent way) and with MpCOP1. Concomitantly, both MpSPA and MpCOP1 could interact with MpHY5, and MpSPA can promote MpCOP1 to ubiquitinate MpHY5 but MpCRY does not regulate the ubiquitination of MpHY5 by MpCOP1/MpSPA complex. These data suggest that COP1/SPA ubiquitinating HY5 is conserved in Marchantia polymorpha, but dissimilar to CRY in Arabidopsis, MpCRY is not an inhibitor of this process under blue light. [ABSTRACT FROM AUTHOR]

Alternative splicing (AS), i.e., generating multiple mRNA transcripts from a single gene, is known to contribute to proteome diversity and gene regulation in eukaryotes. OsHsfA2a, a gene encoding a heat shock transcription factor (HSF) in rice ( Oryza. sativa L. cv. Nipponbare) generates six transcript isoforms ( OsHsfA2a-1 to OsHsfA2a-6) by AS. In this study, an OsHsfA2a has been identified and the genomic sequence found to be composed of three exons and two introns. Moreover, stress-responsive and phytohormone-responsive cis-elements in the promoter regions of OsHsfA2a have been identified. Real-time quantitative polymerase chain reaction analysis has revealed that the six isoforms have different tissue-specific expression patterns under normal growth conditions in rice. Interestingly, when treated with ABA (abscisic acid) and various abiotic stresses such as heat shock, simulated drought and high NaCl, these isoforms also show various stress responsive patterns in rice seedlings. These results indicate that AS of OsHsfA2a may play an important role not only in rice growth and development, but also in regulating stress-specific cellular adaptation responses. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity is considered a critical abiotic stress, limiting crop yields in acid soil. Sweet sorghum (Sorghum bicolor L.) is a promising non-food crop for the manufacturing of industrial products such as sugar, alcohol and biofuel. It mainly grows in Al toxicity widespread tropics and subtropics. Previous studies have demonstrated that LONG HYPOCOTYL5 of sweet sorghum confers transgenic Arabidopsis Al tolerance by modulating the expressions of some typical Al-responsive genes. Here, RNA sequencing analysis revealed that SbHY5 is involved in regulating cell components and cell wall modification, especially the xyloglucan metabolic process (GO: 0010411). Furthermore, all 34 xyloglucan endotransglucosylases/hydrolases (SbXTHs) in sweet sorghum were subjected to bioinformatics analysis and named according to their chromosomal location. Multiple experimental analyses demonstrated that SbHY5 could directly bind to SbXTH7 promoter and downregulate its expression in response to Al toxicity. SbXTH7 expression in root apices and elongation zone significantly downregulated after Al treatment. In addition, SbXTH7 overexpression reduced Arabidopsis Al tolerance by increasing cell wall hemicellulose content and enhancing Al accumulation in roots. In conclusion, we showed the presence of a SbHY5- SbXTH7 axis-mediated hemicellulose-dependent regulatory pathway underlying plant Al tolerance. [Display omitted] • SbHY5 is involved in regulating cell wall hemicellulose xyloglucan metabolic process. • SbHY5 directly binds to the promoter of and downregulates SbXTH7 expression. • The expression of SbXTH7 was specifically depressed by Al stress in root and shoot. • SbXTH7 acts downstream of SbHY5 and plays a negative role under Al stress. • SbXTH7 regulates Al tolerance by modulating hemicellulose content and Al accumulation. [ABSTRACT FROM AUTHOR]