Global identification of LIM genes in response to different heat stress regimes in Lactuca sativa

LIM (Lineage-11 (LIN-11), Insulin-1 (ISL-1), and Mechanotransduction-3 (MEC-3)) genes belong to a family that hold ubiquitous properties contributing to organ, seed, and pollen development as well as developmental and cellular responses to biotic and abiotic stresses. Lettuce (Lactuca sativa) is a highly consumed vegetable crop susceptible heat stress. High temperatures limit lettuce's overall yield, quality and marketability. Lettuce LIM genes have not been identified and their role in response to high temperatures is not known. Aiming to identify potential new targets for thermoresilience, we searched for LIM genes in lettuce and compared them with orthologous of several dicotyledons and monocotyledons plant species.

We identified fourteen lettuce LIM genes distributed into eight different subgroups using a genome-wide analysis strategy. Three belonging to DAR (DA means "large" in Chinese) class I, two DAR class II, one in the WLIM1, two in the WLIM2, one in the PLIM1, two in the PLIM2 class, one ßLIM and two δLIMs. No DAR-like were identified in any of the species analyzed including lettuce. Interestingly, unlike other gene families in lettuce which underwent large genome tandem duplications, LIM genes did not increase in number compared to other plant species. The response to heat stress induced a dynamic transcriptional response on LsLIM genes. All heat stress regimes, including night stress, day stress and day and night stress were largely responsible for changes in LIM transcriptional expression.

Our global analysis at the genome level provides a detailed identification of LIM genes in lettuce and other dicotyledonous and monocotyledonous plant species. Gene structure, physical and chemical properties as well as chromosomal location and Cis-regulatory element analysis together with our gene expression analysis under different temperature regimes identified LsWLIM1, LsWLIM2b, LsDAR3 and LsDAR5 as candidate genes that could be used by breeding programs aiming to produce lettuce varieties able to withstand high temperatures.