Laine, C. | Search bioRxiv

bioRxiv2023

Cellular dynamics in the maize leaf growth zone during recovery from chilling depends on the leaf developmental stage

Zea mays, a major crop, is highly sensitive to chilling which frequently occurs during its seedling stage and negatively affects yields. Although the direct effect of chilling is well-studied, the mechanisms determining the subsequent recovery are still unknown. Our goal is to determine the cellular basis of the dynamic leaf growth response to chilling and during recovery of leaves exposed before or after their emergence. We first studied the effect of a 3-day cold spell on leaf growth at the plant level. Then, we performed a kinematic analysis to analyse the dynamics of cell division and elongation during recovery of the 4th leaf after exposure to cold before or after emergence. Our results demonstrate that cold more strongly reduced the final length of non-emerged than emerged leaves (-13 vs -18%). This was not related to growth differences during cold, but a faster and more complete recovery of the growth of emerged leaves. Kinematic analysis showed that this difference was due to a higher cell division rate on the 1st and a higher cell elongation rate on the 2nd-day of recovery, respectively. The dynamics of cell division and expansion during recovery determine developmental stage-specific differences in cold tolerance of maize leaves.

plant biology↗

bioRxiv2023

Characterization of the Plasmodium berghei regulatory AAA-ATPase subunit Rpt3 as an activator of Protein Phosphatase 1: direct and indirect evidence

The 26S proteasome is the main proteolytic machine involved in protein degradation, thus contributing to homeostasis or stress response of eukaryotic cells. This macromolecular complex, consisting of a 20S core particle assembled with one or two 19S regulatory particles, is highly regulated by phosphorylation. Here we describe the Plasmodium berghei proteasome AAA-ATPase regulatory subunit Rpt3 and show that it binds to protein phosphatase 1, the major parasite phosphatase. In addition, PbRpt3 regulates the activity of the phosphatase both in vitro and in a heterologous model of Xenopus oocytes. Using mutagenesis approaches, we observed that the RVXF motifs of PbRpt3 are involved in this binding and activity. Further use of Xenopus oocyte model and mutagenesis based on the 3D model that we established revealed that the binding capacity of PbRpt3 to ATP may also contribute to its phosphatase-regulating activity. In the parasite, reverse genetic studies suggested an essential role for PbRpt3 since no viable knock-out line could be obtained. Additionally, immunoprecipitation assays followed by mass spectrometry analyses using transgenic PbRpt3-tagged parasites not only confirmed that PbRpt3 belongs to the 19S regulatory particle of the proteasome, but also revealed potential interaction with proteins already shown to play a role in the phospholipid membrane dynamics.

microbiology↗