AUTHOR=Hoogstrate Suzanne W. , van Bussel Lambertus J. A. , Cristescu Simona M. , Cator Eric , Mariani Celestina , Vriezen Wim H. , Rieu Ivo 

TITLE=Tomato ACS4 is necessary for timely start of and progression through the climacteric phase of fruit ripening

JOURNAL=Frontiers in Plant Science

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2014.00466

DOI=10.3389/fpls.2014.00466

ISSN=1664-462X

ABSTRACT=<p>Climacteric fruit ripening, as it occurs in many fruit crops, depends on a rapid, autocatalytic increase in ethylene production. This agriculturally important process has been studied extensively, with tomato simultaneously acting both as a model species and target crop for modification. In tomato, the ethylene biosynthetic genes <italic>ACC SYNTHASE2</italic> (<italic>ACS2</italic>) and <italic>ACS4</italic> are highly expressed during fruit ripening, with a combined loss of both <italic>ACS2</italic> and <italic>ACS4</italic> activity preventing generation of the ethylene burst necessary for fruit ripening. However, the individual roles and importance of <italic>ACS2</italic> and <italic>ACS4</italic> have not been determined. In this study, we examined specifically the role of <italic>ACS4</italic> by comparing the phenotype of an <italic>acs4</italic> mutant firstly with that of the wild-type, and secondly with two novel <italic>ripening-inhibitor</italic> (<italic>rin</italic>) mutants. Ethylene production during ripening was significantly reduced in both <italic>acs4-1</italic>, and <italic>rin</italic> lines, with <italic>rin</italic> genotypes showing the weaker ethylene burst. Also i) the time between anthesis and the start of fruit ripening and ii) the time required to progress through ripening were significantly longer in <italic>acs4-1</italic> than in the wild type, but shorter than in the strongest <italic>rin</italic> mutant. The delay in ripening was reflected in the lower expression of ripening-related transcripts during the mature green and light red ripening stages. Furthermore, expression of <italic>ACS2</italic> and <italic>ACS4</italic> was strongly dependent on a functional <italic>RIN</italic> gene, while <italic>ACS2</italic> expression was largely independent of <italic>ACS4</italic>. Altogether, we show that <italic>ACS4</italic> is necessary for normal progression of tomato fruit ripening and that mutation of this gene may provide a useful means for altering ripening traits.</p>