Genome-Wide Identification, Characterization, and Expression Profile Analysis of CONSTANS-like Genes in Woodland Strawberry (Fragaria vesca)

CONSTANS, a HUB for all seasons: How photoperiod pervades plant physiology regulatory circuits

How does a plant detect the changing seasons and make important developmental decisions accordingly? How do they incorporate daylength information into their routine physiological processes? Photoperiodism, or the capacity to measure the daylength, is a crucial aspect of plant development that helps plants determine the best time of the year to make vital decisions, such as flowering. The protein CONSTANS (CO) constitutes the central regulator of this sensing mechanism, not only activating florigen production in the leaves but also participating in many physiological aspects in which seasonality is important. Recent discoveries place CO in the center of a gene network that can determine the length of the day and confer seasonal input to aspects of plant development and physiology as important as senescence, seed size, or circadian rhythms. In this review, we discuss the importance of CO protein structure, function, and evolutionary mechanisms that embryophytes have developed to incorporate annual information into their physiology.

COL2-dependent photoperiodic floral induction in Nicotiana sylvestris seems to be lost in the N. sylvestris × N. tomentosiformis hybrid N. tabacum

Introduction

Plants are sessile organisms that maximize reproductive success by adapting to their environment. One of the key steps in the reproductive phase of angiosperms is flower development, requiring the perception of multiple endogenous and exogenous signals integrated via a complex regulatory network. Key floral regulators, including the main transcription factor of the photoperiodic pathway (CONSTANS, CO) and the central floral pathway integrator (FLOWERING LOCUS T, FT), are known in many species.

Methods and results

We identified several CO-like (COL) proteins in tobacco (Nicotiana tabacum). The NtCOL2a/b proteins in the day-neutral plant N. tabacum were most closely related to Arabidopsis CO. We characterized the diurnal expression profiles of corresponding genes in leaves under short-day (SD) and long-day (LD) conditions and confirmed their expression in phloem companion cells. Furthermore, we analyzed the orthologs of NtCOL2a/b in the maternal LD ancestor (N. sylvestris) and paternal, facultative SD ancestor (N. tomentosiformis) of N. tabacum and found that they were expressed in the same diurnal manner. NtCOL2a/b overexpression or knock-out using the CRISPR/Cas9 system did not support a substantial role for the CO homologs in the control of floral transition in N. tabacum. However, NsCOL2 overexpression induced flowering in N. sylvestris under typically non-inductive SD conditions, correlating with the upregulation of the endogenous NsFTd gene.

Discussion

Our results suggest that NsFTd is transcriptionally regulated by NsCOL2 and that this COL2-dependent photoperiodic floral induction seems to be lost in N. tabacum, providing insight into the diverse genetics of photoperiod-dependent flowering in different Nicotiana species.

Genome-wide identification, expression analysis, and potential roles under low-temperature stress of bHLH gene family in Prunus sibirica

The basic helix-loop-helix (bHLH) family is one of the most well-known transcription factor families in plants, and it regulates growth, development, and abiotic stress responses. However, systematic analyses of the bHLH gene family in Prunus sibirica have not been reported to date. In this study, 104 PsbHLHs were identified and classified into 23 subfamilies that were unevenly distributed on eight chromosomes. Nineteen pairs of segmental replication genes and ten pairs of tandem replication genes were identified, and all duplicated gene pairs were under purifying selection. PsbHLHs of the same subfamily usually share similar motif compositions and exon-intron structures. PsbHLHs contain multiple stress-responsive elements. PsbHLHs exhibit functional diversity by interacting and coordinating with other members. Twenty PsbHLHs showed varying degrees of expression. Eleven genes up-regulated and nine genes down-regulated in -4°C. The majority of PsbHLHs were highly expressed in the roots and pistils. Transient transfection experiments demonstrated that transgenic plants with overexpressed PsbHLH42 have better cold tolerance. In conclusion, the results of this study have significant implications for future research on the involvement of bHLH genes in the development and stress responses of Prunus sibirica.

Genome-Wide Identification, Characterization and Expression Profiling of the CONSTANS-like Genes in Potato (Solanum tuberosum L.)

CONSTANS-like (COL) genes play important regulatory roles in flowering, tuber formation and the development of the potato (Solanum tuberosum L.). However, the COL gene family in S. tuberosum has not been systematically identified, restricting our knowledge of the function of these genes in S. tuberosum. In our study, we identified 14 COL genes, which were unequally distributed among eight chromosomes. These genes were classified into three groups based on differences in gene structure characteristics. The COL proteins of S. tuberosum and Solanum lycopersicum were closely related and showed high levels of similarity in a phylogenetic tree. Gene and protein structure analysis revealed similarities in the exon-intron structure and length, as well as the motif structure of COL proteins in the same subgroup. We identified 17 orthologous COL gene pairs between S. tuberosum and S. lycopersicum. Selection pressure analysis showed that the evolution rate of COL homologs is controlled by purification selection in Arabidopsis, S. tuberosum and S. lycopersicum. StCOL genes showed different tissue-specific expression patterns. StCOL5 and StCOL8 were highly expressed specifically in the leaves of plantlets. StCOL6, StCOL10 and StCOL14 were highly expressed in flowers. Tissue-specific expression characteristics suggest a functional differentiation of StCOL genes during evolution. Cis-element analysis revealed that the StCOL promoters contain several regulatory elements for hormone, light and stress signals. Our results provide a theoretical basis for the understanding of the in-depth mechanism of COL genes in regulating the flowering time and tuber development in S. tuberosum.