The PATROL1 function in roots contributes to the increase in shoot biomass.

MAIN CONCLUSION: PATOL1 contributes to increasing biomass not only by effective stomatal movement but also by root meristematic activity. PATROL1 (PROTON ATPase TRANSLOCATION CONTROL 1), a protein with a MUN domain, is involved in the intercellular trafficking of AHA1 H+-ATPase to the plasma membrane in guard cells. This allows for larger stomatal opening and more efficient photosynthesis, leading to increased biomass. Although PATROL1 is expressed not only in stomata but also in other tissues of the shoot and root, the role in other tissues than stomata has not been determined yet. Here, we investigated PATROL1 functions in roots using a loss-of-function mutant and an overexpressor. Cytological observations revealed that root meristematic size was significantly smaller in the mutant resulting in the short primary root. Grafting experiments showed that the shoot biomass of the mutant scion was increased when it grafted onto wild-type or overexpressor rootstocks. Conversely, grafting of the overexpressor scion shoot enhanced the growth of the mutant rootstock. The leaf temperatures of the grafted plants were consistent with those of their respective genotypes, indicating cell-autonomous behavior of stomatal movement and independent roles of PATROL1 in plant growth. Moreover, plasma membrane localization of AHA1 was not altered in root epidermal cells in the patrol1 mutant implying existence of a different mode of PATROL1 action in roots. Thus PATROL1 plays a role in root meristem and contributes to increase shoot biomass.

Arabidopsis retromer subunit AtVPS29 is involved in SLY1-mediated gibberellin signaling.

KEY MESSAGE: Retromer protein AtVPS29 upregulates the SLY1 protein and downregulates the RGA protein, positively stimulating the development of the root meristematic zone, which indicates an important role of AtVPS29 in gibberellin signaling. In plants, the large retromer complex is known to play roles in multiple development processes, including cell polarity, programmed cell death, and root hair growth in Arabidopsis. However, many of its roles in plant development remain unknown. Here, we show that Arabidopsis trimeric retromer protein AtVPS29 (vacuolar protein sorting 29) modulates gibberellin signaling. The SLEEPY1 (SLY1) protein, known as a positive regulator of gibberellic acid (GA) signaling, exhibited lower abundance in vps29-3 mutants compared to wild-type (WT) plants. Conversely, the DELLA repressor protein, targeted by the E3 ubiquitin ligase SCF (Skp, Cullin, F-box) complex and acting as a negative regulator of GA signaling, showed increased abundance in vps29-3 mutants compared to WT. The vps29-3 mutants exhibited decreased sensitivity to exogenous GA supply in contrast to WT, despite an upregulation in the expression of GA receptor genes within the vps29-3 mutants. In addition, the expression of the GA synthesis genes was downregulated in vps29-3 mutants, implying that the loss of AtVPS29 causes the downregulation of GA synthesis and signaling. Furthermore, vps29-3 mutants exhibited a reduced meristematic zone accompanied by a decreased cell number. Together, these data indicate that AtVPS29 positively regulates SLY1-mediated GA signaling and plant growth.

Immunolocalization of Jasmonates and Auxins in Pea Roots in Connection with Inhibition of Root Growth under Salinity Conditions.

Inhibition of root elongation is an important growth response to salinity, which is thought to be regulated by the accumulation of jasmonates and auxins in roots. Nevertheless, the mechanisms of the interaction of these hormones in the regulation of the growth response to salinity are still not clear enough. Their better understanding depends on the study of the distribution of jasmonates and auxins between root cells. This was achieved with the help of immunolocalization of auxin (indoleacetic acid) and jasmonates on the root sections of pea plants. Salinity inhibited root elongation and decreased the size of the meristem zone and the length of cells in the elongation zone. Immunofluorescence based on the use of appropriate, specific antibodies that recognize auxins and jasmonates revealed an increased abundance of both hormones in the meristem zone. The obtained data suggests the participation of either auxins or jasmonates in the inhibition of cell division, which leads to a decrease in the size of the meristem zone. The level of only auxin and not jasmonate increased in the elongation zone. However, since some literature evidence argues against inhibition of root cell division by auxins, while jasmonates have been shown to inhibit this process, we came to the conclusion that elevated jasmonate is a more likely candidate for inhibiting root meristem activity under salinity conditions. Data suggests that auxins, not jasmonates, reduce cell size in the elongation zone of salt-stressed plants, a suggestion supported by the known ability of auxins to inhibit root cell elongation.

NADP-MALIC ENZYME 1 Affects Germination after Seed Storage in Arabidopsis thaliana.

Aging decreases the quality of seeds and results in agricultural and economic losses. The damage that occurs at the biochemical level can alter the seed physiological status. Although loss of viability has been investigated frequently, little information exists on the molecular and biochemical factors involved in seed deterioration and loss of viability. Oxidative stress has been implicated as a major contributor to seed deterioration, and several pathways are involved in protection against this. In this study, we show that seeds of Arabidopsis thaliana lacking a functional NADP-MALIC ENZYME 1 (NADP-ME1) have reduced seed viability relative to the wild type. Seeds of the NADP-ME1 loss-of-function mutant display higher levels of protein carbonylation than those of the wild type. NADP-ME1 catalyzes the oxidative decarboxylation of malate to pyruvate with the simultaneous production of CO2 and NADPH. Upon seed imbibition, malate and amino acids accumulate in embryos of aged seeds of the NADP-ME1 loss-of-function mutant compared with those of the wild type. NADP-ME1 expression is increased in imbibed aged as compared with non-aged seeds. NADP-ME1 activity at testa rupture promotes normal germination of aged seeds. In seedlings of aged seeds, NADP-ME1 is specifically active in the root meristematic zone. We propose that NADP-ME1 activity is required for protecting seeds against oxidation during seed dry storage.

Cell Wall Heterogeneity in Root Development of Arabidopsis.

Plant cell walls provide stability and protection to plant cells. During growth and development the composition of cell walls changes, but provides enough strength to withstand the turgor of the cells. Hence, cell walls are highly flexible and diverse in nature. These characteristics are important during root growth, as plant roots consist of radial patterns of cells that have diverse functions and that are at different developmental stages along the growth axis. Young stem cell daughters undergo a series of rapid cell divisions, during which new cell walls are formed that are highly dynamic, and that support rapid anisotropic cell expansion. Once the cells have differentiated, the walls of specific cell types need to comply with and support different cell functions. For example, a newly formed root hair needs to be able to break through the surrounding soil, while endodermal cells modify their walls at distinct positions to form Casparian strips between them. Hence, the cell walls are modified and rebuilt while cells transit through different developmental stages. In addition, the cell walls of roots readjust to their environment to support growth and to maximize nutrient uptake. Many of these modifications are likely driven by different developmental and stress signaling pathways. However, our understanding of how such pathways affect cell wall modifications and what enzymes are involved remain largely unknown. In this review we aim to compile data linking cell wall content and re-modeling to developmental stages of root cells, and dissect how root cell walls respond to certain environmental changes.