Exploring microRNA profiles for circadian clock and flowering development regulation in Himalayan Rhododendron

Recent advancements in the physiological, genetic, and genomic research on Rhododendrons for trait improvement

High species diversity, hybridization potential, broad geographical dispersal range and ornamental characteristics (i.e., attractive size, shape, structure, flowers, and evergreen) have fetched a good international market for Rhododendron. However, most species are restricted to specific geographic areas due to their habitat specificity in acidic soil and cold climates, resulting many species being classified under threat categories of the IUCN. In this review, advances in research on Rhododendron for improvement to floral display quality and stress resistance have been described. The low genetic barrier among species has created opportunities for extensive hybridization and ploidy alteration for introducing quality and adaptive traits during the development of new varieties. Recent technological advances have supported investigations into the mechanism of flower development, as well as cold tolerance and pathogen resistance mechanisms in the Rhododendron. However, most of the species have limited adaptability to drought, line-tolerance, pathogen resistance, and high-temperature conditions and this resistance ability present in few species largely remains unexplored. Additionally, the available genetic diversity and genomic information on species, and possibilities for their application in molecular breeding have been summarized. Overall, genomic resource data are scarce in the majority of the members of this genus. Finally, various research gaps such as genetic mapping of quality traits, understanding the molecular mechanism of quality-related traits and genomic assortment in Rhododendron members have been discussed in the future perspective section.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04006-6.

Small RNA sequencing provides insights into molecular mechanism of flower development in Rhododendron pulchrum Sweet

Rhododendron pulchrum sweet, a member of the Ericaceae family possessing valuable horticultural properties, is widely distributed in the temperate regions. Though serving as bioindicator of metal pollution, the molecular mechanism regulating flowering in R. pulchrum is very limited. Illumina sequencing was performed to identify critical miRNAs in the synthesis of flavonoids at different developmental stages. Totally, 722 miRNAs belonging to 104 families were screened, and 84 novel mature miRNA sequences were predicted. The miR166, miR156, and miR167-1 families were dominant. In particular, 126 miRNAs were significantly differentially expressed among four different flowering stages. Totally, 593 genes were differentially regulated by miRNAs during the flower development process, which were mostly involved in "metabolic pathways", "plant hormone signal transduction", and "mitosis and regulation of biosynthetic processes". In pigment biosynthesis and signal transduction processes, gra-miR750 significantly regulated the expression of flavonoid 3',5'-hydroxylase; aof-miR171a, aof-miR171b, aof-miR171c, cas-miR171a-3p, and cas-miR171c-3p could regulate the expression of DELLA protein; aof-miR390, aof-miR396b, ath-miR3932b-5p, cas-miR171a-3p, aof-miR171a, and aof-miR171b regulated BAK1 expression. This research showed great potentials for genetic improvement of flower color traits for R. pulchrum and other Rhododendron species.

Variations in Circadian Clock Organization & Function: A Journey from Ancient to Recent

Circadian clock components exhibit structural variations in different plant systems, and functional variations during various abiotic stresses. These variations bear relevance for plant fitness and could be important evolutionarily. All organisms on earth have the innate ability to measure time as diurnal rhythms that occur due to the earth's rotations in a 24-h cycle. Circadian oscillations arising from the circadian clock abide by its fundamental properties of periodicity, entrainment, temperature compensation, and oscillator mechanism, which is central to its function. Despite the fact that a myriad of research in Arabidopsis thaliana illuminated many detailed aspects of the circadian clock, many more variations in clock components' organizations and functions remain to get deciphered. These variations are crucial for sustainability and adaptation in different plant systems in the varied environmental conditions in which they grow. Together with these variations, circadian clock functions differ drastically even during various abiotic and biotic stress conditions. The present review discusses variations in the organization of clock components and their role in different plant systems and abiotic stresses. We briefly introduce the clock components, entrainment, and rhythmicity, followed by the variants of the circadian clock in different plant types, starting from lower non-flowering plants, marine plants, dicots to the monocot crop plants. Furthermore, we discuss the interaction of the circadian clock with components of various abiotic stress pathways, such as temperature, light, water stress, salinity, and nutrient deficiency with implications for the reprogramming during these stresses. We also update on recent advances in clock regulations due to post-transcriptional, post-translation, non-coding, and micro-RNAs. Finally, we end this review by summarizing the points of applicability, a remark on the future perspectives, and the experiments that could clear major enigmas in this area of research.

Circadian clock and cell cycle: Cancer and chronotherapy

The circadian clock is an endogenous timing system that ensures that various physiological processes have nearly 24 h circadian rhythms, including cell metabolism, division, apoptosis, and tumor production. In addition, results from animal models and molecular studies underscore emerging links between the cell cycle and the circadian clock. Mutations in the core genes of the circadian clock' can disrupt the cell cycle, which in turn increases the possibility of tumors. At present, tumor chronotherapy, which relies on a circadian clock mechanism, is developing rapidly for optimizing the time of drug administration in tumor treatment to improve drug efficacy and safety. However, the relationship between the circadian clock and the cell cycle is extremely complicated. This review summarizes the possible connection between the circadian clock and the cell cycle. In addition, the review provides evidence of the influence of the circadian clock on senescence and cancer.

MicroRNAs in Woody Plants

MicroRNAs (miRNAs) are small (∼21-nucleotides) non-coding RNAs found in plant and animals. MiRNAs function as critical post-transcriptional regulators of gene expression by binding to complementary sequences in their target mRNAs, leading to mRNA destabilization and translational inhibition. Plant miRNAs have some distinct characteristics compared to their animal counterparts, including greater evolutionary conservation and unique miRNA processing methods. The lifecycle of a plant begins with embryogenesis and progresses through seed germination, vegetative growth, reproductive growth, flowering and fruiting, and finally senescence and death. MiRNAs participate in the transformation of plant growth and development and directly monitor progression of these processes and the expression of certain morphological characteristics by regulating transcription factor genes involved in cell growth and differentiation. In woody plants, a large and rapidly increasing number of miRNAs have been identified, but their biological functions are largely unknown. In this review, we summarize the progress of miRNA research in woody plants to date. In particular, we discuss the potential roles of these miRNAs in growth, development, and biotic and abiotic stresses responses in woody plants.