Arabidopsis B-BOX32 interacts with CONSTANS-LIKE3 to regulate flowering

Abstract

Plants have the ability to respond to seasonal environmental variations by monitoring day length to initiate flowering. The transition from vegetative to the reproductive stage is the critical developmental switch in flowering plants to ensure optimal fitness and/or yield. It has been previously reported that B-BOX32 (BBX32) has the potential to increase grain yield when ectopically expressed in soybean. In the present study, we performed a detailed molecular characterization of the Arabidopsis B-box domain gene BBX32. We showed that the circadian clock in Arabidopsis regulates BBX32 and expressed in the early morning. To understand the molecular mechanism of BBX32 regulation, we performed a large-scale yeast twohybrid screen and identified CONSTANS-LIKE 3 (COL3)/BBX4 as one of its interacting protein partners. Using different genetic and biochemical assays, we have validated this interaction and shown that COL3 targets FT in the presence of BBX32 to regulate the flowering pathway. Based on these findings, we hypothesized that this BBX32-COL3 module could be an additional regulatory mechanism affecting the reproductive development in Arabidopsis that could be translated to crops for increased agricultural productivity.any organisms prepare for seasonal changes by integrating day-length and growth and developmental information. Thus, having a robust mechanism for day-length measurement to thrive in the face of seasonal variations and geographic constraints represents an adaptive advantage for plants. For example, in agriculture, premature flowering affects the overall fitness of the plant, which could lead to dramatic downstream events resulting in loss of crop productivity. The mechanism of flowering has been elucidated through studies describing different physiological and genetic phenotypes in the model species Arabidopsis thaliana (1-3). The mechanism for how plants perceive seasonal variations via sensing the light period, and light quality and further coordination of the network of signaling pathways, has been clearly outlined (1,(3)(4)(5)(6). Arabidopsis, a facultative longday plant, flowers earlier in long days than in short days, in coordination with the circadian clock and photoperiod (7-10). The molecular mechanism of day-length measurement is comprised of the circadian regulation of CONSTANS (CO) gene expression and the light regulation of CO protein stability and activity (11). FLOWERING LOCUS T (FT) protein, expressed in long days, acts as a floral integrator, relaying the signal from the light-sensing leaves via the phloem to the shoot apical meristem (SAM), where flowering is initiated (3, 11). This process, however, occurs only under long-day conditions, when the repression of CO by CYCLING DOF FACTORS1 and 2 (CDF1 and CDF2) is relieved. This derepression is mediated primarily by the interaction of the clock-regulated proteins GIGANTEA (GI) and FLAVIN-BINDING, KELCH REPEAT F-BOX1 (FKF1); GI and FKF1 form a light-dependent complex near the end of long days and targets the CDFs to the proteasome vi...

A PIF1/PIF3-HY5-BBX23 Transcription Factor Cascade Affects Photomorphogenesis

“…In addition, BBX32 regulates photomorphogenesis by interacting with BBX21 and suppressing HY5-regulated gene expression (Holtan et al, 2011). BBX32 can also interact with BBX4 to regulate the flowering pathway (Tripathi et al, 2017).…”

CONSTANS Imparts DNA Sequence Specificity to the Histone Fold NF-YB/NF-YC Dimer

“…Among the downregulated genes in co-sail, we find many members of the B-box protein (BBX) family (Khanna et al, 2009), mostly those that do not contain a CCT domain. These include BBX19 (At4g38960), whose protein product interacts with CO and whose reduced expression accelerates flowering , and BBX30 (At4g15248) and BBX31 (At3g21890), which also interact with the CO protein and whose overexpression delays flowering (Graeff et al, 2016), as well as BBX32, which interacts with COL3 to regulate FT (Tripathi et al, 2017).…”

Circadian clock components control daily growth activities by modulating cytokinin levels and cell division‐associated gene expression in Populus trees

“…Arabidopsis cca1;lhy mutants, moreover, show an earlier phase of BBX32 expression. In Populus , LHY1 , LHY2 , BBX19 , and BBX32 are coexpressed in WT and have a significantly earlier phase of expression in lhy‐10 (Figure d), mirroring BBX32 expression in Arabidopsis (Tripathi et al, ). Importantly, the phasing of BBX19 and BBX32 may be part of a clock‐associated growth control mechanism across diverse species, including Arabidopsis, soybean and Populus (Figure ).…”

“…Further, overexpression of BBX32 sets the hypocotyl elongation phase to the dark period in Arabidopsis (Holtan et al, ) and increases yield of soybean ( Glycine max ; Preuss et al, ). Recent data from Arabidopsis suggest BBX32 is part of a regulatory loop with CCA1 and/or LHY, because overexpression of BBX32 increases both their expression and circadian period length (Tripathi, Carvallo, Hamilton, Preuss, & Kay, ). Arabidopsis cca1;lhy mutants, moreover, show an earlier phase of BBX32 expression.…”

“…We propose that maximal expression of LHY1 and LHY2 during the morning promotes growth by activating genes such as BBX19 and BBX32 and that this affects CK biosynthesis and responses. These features may be linked; up‐regulation of BBX32 in soybean gives a “stay green” phenotype consistent with high CK levels (Preuss et al, ), and CK perception and response proteins interact with Arabidopsis BBX32 (Tripathi et al, ). Our findings match reports of daily leaf growth rhythms in Populus deltoides , which shows high rates of growth during the evening and night (Matsubara et al, ).…”