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Lopez-Juez, E.

Publications and source records attributed to Lopez-Juez, E..

2 recordsLinked to original sources
bioRxiv2025

An ARF2-GRF5 module, operating early and upstream of GLK factors, reveals genetic hierarchy during chloroplast biogenesis

O_LIOur current understanding of the regulation of chloroplast development lags behind that of the process itself. The GOLDEN2-LIKE (GLK) factors drive the expression of photosynthesis-associated nuclear (PhAN) genes. Simultaneous loss of GLK1 and GLK2 in Arabidopsis plants leads to pale-green, incompletely-developed chloroplasts. This highlights the GLKs role but also the involvement of other components. C_LIO_LIWe hypothesised that further regulators could be found by searching for suppressor mutations of a severe glk1 knock-down (KD) glk2 knock-out (KO) mutant. We identified suppressor of glks (sgl) 2, sgl2. C_LIO_LIThe sgl2 glk1 glk2 triple mutant showed significant increases in chlorophyll, expression of PhAN genes, chloroplast thylakoid stacking, and cellular volume of chloroplasts. sgl2 was caused by loss of function of AUXIN RESPONSE FACTOR2, ARF2. arf2sgl2 boosted chloroplast content as a single mutant, and dramatically suppressed the chloroplast delay of the phytochrome-deficient long hypocotyl 1 (hy1) mutant. Overexpression of Growth Regulating Factor 5 (GRF5), which is negatively regulated by ARF2, also rescued chlorophyll levels in glk1 glk2, confirming a role for ARF2 and GRF5 as a transcription module. We observed in glk1 glk2 low but detectable expression of GLK1, which was elevated in arf2sgl2 glk1 glk2, and saw reduced suppression by arf2sgl2 of the phenotype of a separate glk1-2 glk2-2 mutant carrying two KO alleles, revealing partial epistasis. Presumed orthologs of ARF2 and GRF5 are expressed very early in developing cereal leaves, well ahead of the bulk of GLK expression during the greening stage. C_LIO_LIOur results place ARF2 as a negative switch modulating GRF5 early and upstream, whether directly or indirectly, of GLK factors, but also acting independently from them. This reveals a hierarchy of transcription factor action and feed-forward regulation in chloroplast biogenesis during leaf development. C_LI

plant biology↗
bioRxiv2022

Mutations in TIC100 impair and repair chloroplast protein import and impact retrograde signalling

Chloroplast biogenesis requires synthesis of proteins in the nucleocytoplasm and the chloroplast itself. Nucleus-encoded chloroplast proteins are imported via multiprotein translocons in the organelles envelope membranes. Controversy exists around whether a 1 MDa complex comprising TIC20, TIC100 and other proteins constitutes the inner membrane TIC translocon. The Arabidopsis cue8 virescent mutant is broadly defective in plastid development. We identify CUE8 as TIC100. The tic100cue8 mutant accumulates reduced levels of 1 MDa complex components and exhibits reduced import of two nucleus-encoded chloroplast proteins of different import profiles. A search for suppressors of tic100cue8 identified a second mutation within the same gene, tic100soh1, which rescues the visible, 1 MDa complex-subunit abundance, and chloroplast protein import phenotypes. tic100soh1 retains but rapidly exits virescence, and rescues the synthetic lethality of tic100cue8 when retrograde signalling is impaired by the gun1 mutation. Alongside the strong virescence, changes in RNA editing and the presence of unimported precursor proteins show that a strong signalling response is triggered when TIC100 function is altered. Our results are consistent with a role for TIC100, and by extension the 1 MDa complex, in the chloroplast import of photosynthetic and non-photosynthetic proteins, a process which initiates retrograde signalling. One sentence summaryComplementary mutations in TIC100 of the chloroplast inner envelope membrane cause reductions or corrective improvements in chloroplast protein import, and highlight a signalling role.

plant biology↗