Involvement of CONSTANS-like Proteins in Plant Flowering and Abiotic Stress Response

Abstract

The process of flowering in plants is a pivotal stage in their life cycle, and the CONSTANS-like (COL) protein family, known for its photoperiod sensing ability, plays a crucial role in regulating plant flowering. Over the past two decades, homologous genes of COL have been identified in various plant species, leading to significant advancements in comprehending their involvement in the flowering pathway and response to abiotic stress. This article presents novel research progress on the structural aspects of COL proteins and their regulatory patterns within transcription complexes. Additionally, we reviewed recent information about their participation in flowering and abiotic stress response, aiming to provide a more comprehensive understanding of the functions of COL proteins.

Keywords: CONSTANS-like; abiotic stress; flowering time; photoperiod; transcription complex.

Figure 1

CONSTANS (CO) transcription complex “recruitment” model. NY-FB and NF-YC physically bind to CO through the CCT domain and provide a scaffold to assist CO binding to the CORR region of pFT. NY-FA/YB/YC trimeric complexes can bind to multiple sites on pFT to promote the formation of chromatin loops at this specific sites, facilitating its proximity to the CORR motif, and ultimately promoting the binding of NF-YB/YC/CO complex to CORR elements through the function of unknown factor (long dashed arrow). Other COL members may participate in the assembly of CO complexes through interactions between B-box domains (short dashed arrow). The solid arrow represents the promotion of FT expression by the CO complex.

Figure 2

CONSTANS (CO) photoperiodic flowering pathway. Background color represents change from morning to evening during the day (left to right). In the morning, CO transcription levels are inhibited by the CDF1-TPL complex. In the afternoon, blue light can stabilize FKF1/ZTL, thereby releasing inhibition of CDF1. Positive transcriptional regulators such as TCP also facilitate transcription. CO mRNA levels accumulate to a peak. Similarly, at protein level, CO abundance gradually increases and reaches its highest level in the afternoon, with a small peak in the morning, possibly due to the action of FKBP12. After that, members such as PHYB and HOS1 quickly control CO abundance to avoid its premature accumulation. Until the afternoon, PHYA, FKF1, and CRY2 relieve CO degradation by COP1.

Figure 3

Effects of abiotic stress (drought, cold, salt) on the photoperiodic pathway in Arabidopsis. Blue and yellow circles represent photoperiodic members in leaf and shoot apical meristem (SAM), respectively (these two positions are marked with dashed circles). Black arrows represent transmission of photoperiodic signals. Drought stress signals can directly affect GI, FT, and SOC1 in the photoperiodic pathway through SVP and ABF to promote plant flowering (red arrow). Salt stress signals can promote degradation of GI and interfere with FT function by inducing BFT/TFL1 to hinder plant flowering (brown arrow). Cold stress signals can indirectly block CO, FT, and SOC1 in the photoperiodic pathway to delay plant flowering. Cold can also directly induce GI and release CDF to improve plant cold tolerance (blue arrow).

Figure 4

Involvement of COLs from different species in stress responses. Among them, AtCOL10 is involved in cold response; MdCOL9, Ghd2, BnCOL2, GmCOL1a, and MiCOL16 are involved in drought response; GmCOL1a, MiCOL16, ThCOL2, AtCO, and AtCOL4 are involved in salt response; BnCOL2, AtCOL4, ZmCOL, and HaCOL are involved in ABA regulation; and ThCOL2 and OMG1 are involved in ROS regulation. ThCOL2 is also involved in MDA regulation, and indirectly involved in plant stress response.