Co-condensation with photoexcited cryptochromes facilitates MAC3A to positively control hypocotyl growth in Arabidopsis

The Arabidopsis blue-light photoreceptor CRY2 is active in darkness to inhibit root growth

Cryptochromes (CRYs) are blue-light receptors that regulate diverse aspects of plant growth. However, whether and how non-photoexcited CRYs function in darkness or non-blue-light conditions is unknown. Here, we show that CRY2 affects the Arabidopsis transcriptome even in darkness, revealing a non-canonical function. CRY2 suppresses cell division in the root apical meristem to downregulate root elongation in darkness. Blue-light oligomerizes CRY2 to de-repress root elongation. CRY2 physically interacts with FORKED-LIKE 1 (FL1) and FL3, and these interactions are inhibited by blue light, with only monomeric but not dimeric CRY2 able to interact. FL1 and FL3 associate with the chromatin of cell division genes to facilitate their transcription. This pro-growth activity is inhibited by CRY2's physical interaction with FLs in darkness. Plants have evolved to perceive both blue-light and dark cues to coordinate activation and repression of competing developmental processes in above- and below-ground organs through economical and dichotomous use of ancient light receptors.

GLR36T807I Mutation of Casuarina equisetifoli Is Associated With a Decreased JA Response to Insect Feeding by Lymantria xylina

Lymantria xylina is the most important defoliator, damaging the effective coastal windbreak tree species Casuarina equisetifolia. However, the underlying genetic mechanisms through which C. equisetifolia responds to L. xylina attacks remain unknown. Here, we compared the transcriptional, phytohormone and metabolic differences between susceptible (S) and resistant (R) C. equisetifolia cultivars in response to L. xylina feeding. The main L. xylina-induced resistance in C. equisetifolia was a jasmonate (JA) response and JA synthesis was highly induced by L. xylina feeding at both the transcriptional and metabolic levels, thus promoting flavonoid accumulation. The JA response was highly activated by L. xylina feeding on the R but not in the S cultivar, although the JA signalling pathway was intact in both cultivars. We found a single amino acid mutation in the homologues of glutamate receptor-like protein 3.6 (CeGLR3.6T807I) in the S cultivar. Compared with the GLR3.6 homologues in the R cultivar, phosphorylation of CeGLR3.6T807I was not induced by insect feeding, leading to a decreased JA response in the S cultivar. Collectively, this study provides new insights into the function of CeGLR3.6 in regulating the JA response of C. equisetifolia to L. xylina feeding.

Light-induced cryptochrome 2 liquid-liquid phase separation and mRNA methylation

Light is essential not only for photosynthesis but also for the regulation of various physiological and developmental processes in plants. While the mechanisms by which light regulates transcription and protein stability are well established, the effects of light on RNA methylation and their subsequent impact on plant growth and development are less understood. Upon exposure to blue light, the photoreceptor cryptochromes form nuclear speckles or nuclear bodies, termed CRY photobodies. The CRY2 photobodies undergo light-induced homo-oligomerization and liquid-liquid phase separation (LLPS), which are crucial for their physiological activity. Recent studies have proposed that blue light-induced CRY2 LLPS increases the local concentration or directly enhances the biochemical activities of RNA N6-methyladenosine (m6A) methyltransferases, thus, to regulate circadian clock and maintain Chl homeostasis through processes of RNA decay or translation. This review aimed to elucidate the functions of CRY2 and LLPS in RNA methylation, focusing on the light-controlled reversible phase transitions regulon and the outstanding questions that remain in RNA methylation.

GhMAC3e is involved in plant growth and defense response to Verticillium dahliae

KEY MESSAGE

GhMAC3e expression was induced by various stresses and hormones. GhMAC3e may regulate plant growth by influencing auxin distribution, and play important roles in Verticillium wilt resistance via mediating SA signaling. The MOS4-Associated Complex (MAC) is a highly conserved protein complex involved in pre-mRNA splicing and spliceosome assembly, which plays a vital role in plant immunity. It comprises key components such as MOS4, CDC5, and PRL1. MAC3A/B, as U-box E3 ubiquitin ligases, are crucial for various plant processes including development, stress responses, and disease resistance. However, their roles in cotton remain largely unknown. In this study, we first cloned the GhMAC3e gene from cotton and explored its biological functions by using virus-induced gene silencing (VIGS) in cotton and transgenic overexpression in Arabidopsis. The results showed that GhMAC3e is ubiquitously expressed in cotton tissues and could be induced by salt stress, Verticillium dahliae (VD) infection, PEG, ABA, ETH, GA3, MeJA, and SA. Silencing GhMAC3e retarded primary stem growth and reduced biomass of cotton coupled with the reduced auxin content in the petioles and veins. Silencing GhMAC3e up-regulated expression of cell growth-related genes GhXTH16 and Gh3.6, while down-regulated GhSAUR12 expression. Ectopic expression of GhMAC3e in Arabidopsis significantly enhanced its resistance to Verticillium wilt (VW) in terms of decreased pathogen biomass and lowered plant mortality. Overexpression of GhMAC3e dramatically upregulated AtPR1 by around 15 fold and more than 262 fold under basal and VD inoculation condition, respectively. This change was not associated with the expression of GhNPR1. In conclusion, GhMAC3e may not only regulate plant growth by influencing auxin distribution and growth-related gene expression, but also play important roles in VW resistance via mediating SA signaling independent of NPR1 transcription level.

The dual-action mechanism of Arabidopsis cryptochromes

Photoreceptor cryptochromes (CRYs) mediate blue-light regulation of plant growth and development. It has been reported that Arabidopsis CRY1and CRY2 function by physically interacting with at least 84 proteins, including transcription factors or co-factors, chromatin regulators, splicing factors, messenger RNA methyltransferases, DNA repair proteins, E3 ubiquitin ligases, protein kinases and so on. Of these 84 proteins, 47 have been reported to exhibit altered binding affinity to CRYs in response to blue light, and 41 have been shown to exhibit condensation to CRY photobodies. The blue light-regulated composition or condensation of CRY complexes results in changes of gene expression and developmental programs. In this mini-review, we analyzed recent studies of the photoregulatory mechanisms of Arabidopsis CRY complexes and proposed the dual mechanisms of action, including the "Lock-and-Key" and the "Liquid-Liquid Phase Separation (LLPS)" mechanisms. The dual CRY action mechanisms explain, at least partially, the structural diversity of CRY-interacting proteins and the functional diversity of the CRY photoreceptors.

Light signaling in plants-a selective history

In addition to providing the radiant energy that drives photosynthesis, sunlight carries signals that enable plants to grow, develop and adapt optimally to the prevailing environment. Here we trace the path of research that has led to our current understanding of the cellular and molecular mechanisms underlying the plant's capacity to perceive and transduce these signals into appropriate growth and developmental responses. Because a fully comprehensive review was not possible, we have restricted our coverage to the phytochrome and cryptochrome classes of photosensory receptors, while recognizing that the phototropin and UV classes also contribute importantly to the full scope of light-signal monitoring by the plant.

Light-induced LLPS of the CRY2/SPA1/FIO1 complex regulating mRNA methylation and chlorophyll homeostasis in Arabidopsis

Light regulates chlorophyll homeostasis and photosynthesis via various molecular mechanisms in plants. The light regulation of transcription and protein stability of nuclear-encoded chloroplast proteins have been extensively studied, but how light regulation of mRNA metabolism affects abundance of nuclear-encoded chloroplast proteins and chlorophyll homeostasis remains poorly understood. Here we show that the blue light receptor cryptochrome 2 (CRY2) and the METTL16-type m6A writer FIONA1 (FIO1) regulate chlorophyll homeostasis in response to blue light. In contrast to the CRY2-mediated photo-condensation of the mRNA adenosine methylase (MTA), photoexcited CRY2 co-condenses FIO1 only in the presence of the CRY2-signalling protein SUPPRESSOR of PHYTOCHROME A (SPA1). CRY2 and SPA1 synergistically or additively activate the RNA methyltransferase activity of FIO1 in vitro, whereas CRY2 and FIO1, but not MTA, are required for the light-induced methylation and translation of the mRNAs encoding multiple chlorophyll homeostasis regulators in vivo. Our study demonstrates that the light-induced liquid-liquid phase separation of the photoreceptor/writer complexes is commonly involved in the regulation of photoresponsive changes of mRNA methylation, whereas the different photo-condensation mechanisms of the CRY/FIO1 and CRY/MTA complexes explain, at least partially, the writer-specific functions in plant photomorphogenesis.