Abstract
Monocarpic plants have a single reproductive phase, in which their longevity is developmentally programmed by molecular networks. In the reproductive phase of Arabidopsis thaliana, the inflorescence meristem (IM) maintains a central pool of stem cells and produces a limited number of flower primordia, which result in seed formation and the death of the whole plant. In this study, we observed morphological changes in the IM at cellular and intracellular resolutions until the end of the plant life cycle. We observed four biological events during the periods from 1 week after bolting (WAB) till the death of stem cells: (1) the gradual reduction in the size of the IM, (2) the dynamic vacuolation of IM cells, (3) the loss of the expression of the stem cell determinant WUSCHEL (WUS), and (4) the upregulation of the programmed cell death marker BIFUNCTIONAL NUCLEASE1 (BFN1) in association with the death of stem cells. These results indicate that the stem cell population gradually decreases in IM during plant aging and eventually is fully terminated. We further show that the expression of WUS became undetectable in IM at 3 WAB prior to the loss of CLAVATA3 (CLV3) expression at 5 WAB; CLV3 is a negative regulator of WUS. Moreover, clv3 plants showed delayed loss of WUS and lived 6 weeks longer compared with wild-type plants. These results indicated that the prolonged expression of CLV3 at 4–5 WAB may be a safeguard that inhibits the reactivation of WUS and promotes plant death. Finally, through transcriptome analysis, we determined that reactive oxygen species (ROS) are involved in the control of plant longevity. Our work presents a morphological and physiological framework for the regulation of plant longevity in Arabidopsis.
Highlights
How plants control their longevities is a conundrum that has puzzled botanists for decades (Thomas, 2013; Dijkwel and Lai, 2019)
To generate the proBFN1:GUS-green fluorescent protein (GFP) construct, a genomic DNA fragment covering a sequence 2.0 kb upstream of the BIFUNCTIONAL NUCLEASE1 (BFN1) translation start site was subcloned into the pENTR/D-TOPO vector according to the manufacturer’s protocol (Thermo Fisher, Germany)
Combined with the results regarding plant growth (Figure 1) and inflorescence meristem (IM) size (Figure 2), these results suggested that even stem cells in the IM were getting differentiated and IMs lost their proliferative activity at approximately 4 week after bolting (WAB)
Summary
How plants control their longevities is a conundrum that has puzzled botanists for decades (Thomas, 2013; Dijkwel and Lai, 2019). The life spans of some species range from several weeks in annuals to thousands of years (Burian et al, 2016). Compared with those long-lived species, the monocarpic plant Arabidopsis [ecotype Landsberg erecta (Ler)]. Plant Longevity in Arabidopsis has a relatively short life cycle, which is maintained at 50– 70 days from seed germination to the formation of the generation (Hensel et al, 1993). All further aboveground cells, tissues, and organs are regarded as descendants of stem cells in the CZ of the SAM and IM (Burian et al, 2016). The SAM and IM are sometimes called the “fountain of youth” in plants (Baurle and Laux, 2003), and it is clear that stem cells hold the key to plant life span (Dijkwel and Lai, 2019); i.e., the activities of stem cells are a key factor in plant life span
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