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Summary: In leaves of C4 plants, the reactions of photosynthesis become restricted between two compartments. Typically, this allows accumulation of C4 acids in mesophyll (M) cells and subsequent decarboxylation in the bundle sheath (BS). In C4 grasses, proliferation of plasmodesmata between these cell types is thought to increase cell‐to‐cell connectivity to allow efficient metabolite movement. However, it is not known whether C4 dicotyledons also show this enhanced plasmodesmal connectivity and so whether this is a general requirement for C4 photosynthesis is not clear. How M and BS cells in C4 leaves become highly connected is also not known.We investigated these questions using 3D‐ and 2D‐electron microscopy on the C4 dicotyledon Gynandropsis gynandra as well as phylogenetically close C3 relatives.The M–BS interface of C4G. gynandra showed higher plasmodesmal frequency compared with closely related C3 species. Formation of these plasmodesmata was induced by light. Pharmacological agents that perturbed photosynthesis reduced the number of plasmodesmata, but this inhibitory effect could be reversed by the provision of exogenous sucrose.We conclude that enhanced formation of plasmodesmata between M and BS cells is wired to the induction of photosynthesis in C4G. gynandra. [ABSTRACT FROM AUTHOR]

Amylose-free (waxy) maize has been a vegetable (cooked ears) and staple food in Southeast Asia for centuries, resulting in hundreds of landraces (LRs) across the region. The recessive waxy allele induces soft grains with preferred cooking and flavour properties. We hypothesized that eating preferences resulted in the additional selection for different starch properties, reflected in altered starch granule morphology or amylopectin structure. A total of 41 LRs were available as starting material that had been used by different ethnic groups in Vietnam and Thailand. Unluckily, some LRwere not pure waxy, but we successfully regained the original pure waxy status for most. Twenty LR were chosen for analysis of starch traits according to their purity. Four different waxy mutationswere identified, including two unknown alleles. This is a strong proof for parallel independent selection of waxy maize in the region. Starch granule morphology and size were similar among all LRs. Gelatinization properties differed only between waxy and wild-type LR, and all waxy LR were comparable to a commercial waxy hybrid. The fine structure of waxy amylopectin had fewer short chains compared with that in wild-type. So far, the differences observed in starch properties are likely associated exclusively with the waxy trait. Despite the strong selection for amylose-free starch, there was no evidence for additional region wide selection for other special starch properties in our collection. In conclusion, all analyses did not encourage further targeted research on allelic variation of other starch metabolism genes for future use in the food and feed industry. [ABSTRACT FROM AUTHOR]

To uncover components of the mechanism that adjusts the rate of leaf starch degradation to the length of the night, we devised a screen for mutant Arabidopsis thaliana plants in which starch reserves are prematurely exhausted. The mutation in one such mutant, named early starvation1 (esv1), eliminates a previously uncharacterized protein. Starch in mutant leaves is degraded rapidly and in a nonlinear fashion, so that reserves are exhausted 2 h prior to dawn. The ESV1 protein and a similar uncharacterized Arabidopsis protein (named Like ESV1 [LESV]) are located in the chloroplast stroma and are also bound into starch granules. The region of highest similarity between the two proteins contains a series of near-repeated motifs rich in tryptophan. Both proteins are conserved throughout starch-synthesizing organisms, from angiosperms and monocots to green algae. Analysis of transgenic plants lacking or overexpressing ESV1 or LESV, and of double mutants lacking ESV1 and another protein necessary for starch degradation, leads us to propose that these proteins function in the organization of the starch granule matrix. We argue that their misexpression affects starch degradation indirectly, by altering matrix organization and, thus, accessibility of starch polymers to starch-degrading enzymes. [ABSTRACT FROM AUTHOR]

The article provides information on the role of two starch-bound proteins, LESV and ESV1, in promoting the phase transition of amylopectin-like glucans, which are the main components of starch in plants. These proteins facilitate the alignment and crystallization of glucan double helices, leading to the formation of semi-crystalline granules.

In leaves of C 4 plants, the reactions of photosynthesis become restricted between two compartments. Typically, this allows accumulation of C 4 acids in mesophyll (M) cells and subsequent decarboxylation in the bundle sheath (BS). In C 4 grasses, proliferation of plasmodesmata between these cell types is thought to increase cell-to-cell connectivity to allow efficient metabolite movement. However, it is not known whether C 4 dicotyledons also show this enhanced plasmodesmal connectivity and so whether this is a general requirement for C 4 photosynthesis is not clear. How M and BS cells in C 4 leaves become highly connected is also not known. We investigated these questions using 3D- and 2D-electron microscopy on the C 4 dicotyledon Gynandropsis gynandra as well as phylogenetically close C 3 relatives. The M-BS interface of C 4 G. gynandra showed higher plasmodesmal frequency compared with closely related C 3 species. Formation of these plasmodesmata was induced by light. Pharmacological agents that perturbed photosynthesis reduced the number of plasmodesmata, but this inhibitory effect could be reversed by the provision of exogenous sucrose. We conclude that enhanced formation of plasmodesmata between M and BS cells is wired to the induction of photosynthesis in C 4 G. gynandra., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)