Tomato UVI4 homologue modulates cell expansion to participate heat-stimulated hypocotyl elongation

Abstract

Raising incubation temperature during seed germination is a conventional strategy to promote the efficiency of seed emergence from soil, which requires robust hypocotyl elongation. Tomato hypocotyl elongation is a consequence of active cell division and expansion, both of which require precisely regulated cell cycle progression. Anaphase-promoting complex/cyclosome (APC/C) is a multiple subunit E3 ubiquitin ligase which degrades certain mitotic cyclins and inhibit M-specific CDK/cyclin complex activity during cell cycle from G2 to M phase. Little is known about the function of APC/C regulators during tomato hypocotyl elongation. Here, we isolated tomato homologue SlUVI4 based on the homology with the negative regulator of APC/C, UVI4 in Arabidopsis. SlUVI4 had high expression in hypocotyls after the seed germination and gradually reduced its transcription during the hypocotyl elongation. We probed SlUVI4 function in heat-stimulated hypocotyl elongation through genetic, physiological and cytological analyses. Both overexpression and loss-of-function of SlUVI4 resulted in defective hypocotyl growth with opposite cell sizes. Microscopic analyses of hypocotyl sections revealed that SlUVI4 plays important roles in repressing cell expansion. Heat repressed SlUVI4 transcription to stimulate cell expansion and hypocotyl elongation. Inhibition of auxin polar transportation activated SlUVI4 transcription and abolished heat-induced cell expansion and hypocotyl elongation. Exogenous auxin repressed SlUVI4 transcription and enhanced hypocotyl elongation under heat condition. Partial loss of function of SlUVI4 largely abrogated heat-stimulated hypocotyl cell expansion. Taken together, our findings illustrate that SlUVI4 is involved in auxin-mediated hypocotyl elongation stimulated by heat. • SlUVI4 negatively modulates cell expansion in tomato hypocotyls. • Auxin represses SlUVI4 transcription in tomato hypocotyls. • Heat-stimulated hypocotyl elongation requires auxin-mediated repression of SlUVI4 transcription.