Ruslana Radchuk’s research while affiliated with Leibniz Institute of Plant Genetics and Crop Plant Research and other places

Plants undergo several developmental transitions during their life cycle. One of these, the differentiation of the young embryo from a meristem‐like structure into a highly specialized storage organ, is believed to be controlled by local connections between sugars and hormonal response systems. However, we know little about the regulatory networks underpinning the sugar–hormone interactions in developing seeds. By modulating the trehalose 6‐phosphate (T6P) content in growing embryos of garden pea (Pisum sativum), we investigate here the role of this signaling sugar during the seed‐filling process. Seeds deficient in T6P are compromised in size and starch production, resembling the wrinkled seeds studied by Gregor Mendel. We show also that T6P exerts these effects by stimulating the biosynthesis of the pivotal plant hormone, auxin. We found that T6P promotes the expression of the auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE RELATED2 (TAR2), and the resulting effect on auxin concentrations is required to mediate the T6P‐induced activation of storage processes. Our results suggest that auxin acts downstream of T6P to facilitate seed filling, thereby providing a salient example of how a metabolic signal governs the hormonal control of an integral phase transition in a crop plant.

Plants undergo several developmental transitions during their life cycle. One of these, the differentiation of the young embryo from a meristem-like structure into a highly-specialized storage organ, is vital to the formation of a viable seed. For crops in which the seed itself is the end product, effective accumulation of storage compounds is of economic relevance, defining the quantity and nutritive value of the harvest yield. However, the regulatory networks underpinning the phase transition into seed filling are poorly understood. Here we show that trehalose 6-phosphate (T6P), which functions as a signal for sucrose availability in plants, mediates seed filling processes in seeds of the garden pea, a key grain legume. Seeds deficient in T6P are compromised in size and starch production, resembling the wrinkled seeds studied by Gregor Mendel. We show also that T6P exerts these effects by stimulating the biosynthesis of the pivotal plant hormone, auxin. We found that T6P promotes the expression of the auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE RELATED2 (TAR2), and the resulting effect on auxin levels is required to mediate the T6P-induced activation of storage processes. Our results suggest that auxin acts downstream of T6P to facilitate seed filling, thereby providing a salient example of how a metabolic signal governs the hormonal control of an integral phase transition in a crop plant.

This is a Research Highlight about Radchuk et al. To view this article visit https://doi.org/10.1111/tpj.14363 June 2019The Plant Journal 98(6):959-960 DOI: 10.1111/tpj.14418

Cover page - Radschuk et al. 2019 - The Plant Journal

Phylogenetically‐related groups of species contain lineage‐specific genes, which exhibit no sequence similarity to any genes outside of the lineage. We describe here that the Jekyll gene, required for sexual reproduction, exists in two much diverged allelic variants, Jek1 and Jek3. Despite low similarity, the Jek1 and Jek3 proteins share identical signal peptides, conserved cysteine positions and direct repeats. The Jek1/Jek3 sequences are located at the same chromosomal locus and inherited by monogenic Mendelian fashion. Jek3 has similar expression as Jek1 and complements the Jek1 function in Jek1‐defficient plants. Jek1 and Jek3 allelic variants were almost equally distributed in a collection of 485 wild and domesticated barley accessions. All domesticated barleys harboring the Jek1 allele belong to single haplotype J1‐H1 indicating a genetic bottleneck during domestication. Domesticated barleys harboring the Jek3 allele consisted of three haplotypes. Jekyll‐like sequences were found only in species of the closely related tribes Bromeae and Triticeae but not in other Poaceae. Non‐invasive magnetic resonance imaging revealed intrinsic grain structure in Triticeae and Bromeae, associated with the Jekyll function. The emergence of Jekyll suggests its role in separation of the Bromeae and Triticeae lineages within the Poaceae and identifies the Jekyll genes as lineage‐specific. This article is protected by copyright. All rights reserved.

The angiosperm embryo and endosperm are limited in space because they grow inside maternal seed tissues. The elimination of cell layers of the maternal seed coat by programmed cell death ( PCD ) could provide space and nutrition to the filial organs. Using the barley ( Hordeum vulgare L.) seed as a model, we elucidated the role of vacuolar processing enzyme 4 ( VPE 4) in cereals by using an RNA i approach and targeting the enzymatic properties of the recombinant protein. A comparative characterization of transgenic versus wild‐type plants included transcriptional and metabolic profiling, flow cytometry, histology and nuclear magnetic imaging of grains. The recombinant VPE 4 protein exhibited legumain and caspase‐1 properties in vitro . Pericarp disintegration was delayed in the transgenic grains. Although the VPE 4 gene and enzymatic activity was decreased in the early developing pericarp, storage capacity and the size of the endosperm and embryo were reduced in the mature VPE 4‐repressed grains. The persistence of the pericarp in the VPE 4‐affected grains constrains endosperm and embryo growth and leads to transcriptional reprogramming, perturbations in signalling and adjustments in metabolism. We conclude that VPE 4 expression executes PCD in the pericarp, which is required for later endosperm filling, and argue for a role of PCD in maternal control of seed size in cereals.