Integrative analysis of the late maturation programme and desiccation tolerance mechanisms in intermediate coffee seeds.

Stéphane Dussert,Eveline Déchamp,Valérie Rofidal,Aldecinei Bastos-Siqueira,Julien Serret,Fabienne Morcillo,Philippe Lashermes,Hervé Etienne,Thierry Joët

doi:10.1093/jxb/erx492

Abstract

The 'intermediate seed' category was defined in the early 1990s using coffee (Coffea arabica) as a model. In contrast to orthodox seeds, intermediate seeds cannot survive complete drying, which is a major constraint for seed storage and has implications for both biodiversity conservation and agricultural purposes. However, intermediate seeds are considerably more tolerant to drying than recalcitrant seeds, which are highly sensitive to desiccation. To gain insight into the mechanisms governing such differences, changes in desiccation tolerance (DT), hormone contents, and the transcriptome were analysed in developing coffee seeds. Acquisition of DT coincided with a dramatic transcriptional switch characterised by the repression of primary metabolism, photosynthesis, and respiration, and the up-regulation of genes coding for late-embryogenesis abundant (LEA) proteins, heat-shock proteins (HSPs), and antioxidant enzymes. Analysis of the heat-stable proteome in mature coffee seeds confirmed the accumulation of LEA proteins identified at the transcript level. Transcriptome analysis also suggested a major role for ABA and for the transcription factors CaHSFA9, CaDREB2G, CaANAC029, CaPLATZ, and CaDOG-like in DT acquisition. The ability of CaHSFA9 and CaDREB2G to trigger HSP gene transcription was validated by Agrobacterium-mediated transformation of coffee somatic embryos.

Highlights

The seed is a key structure in the life cycle of higher plants; it the majority of flowering plants produce seeds that are able facilitates dispersal in space and over time, and to withstand almost complete loss of cellular water
These seven developmental stages can be briefly described as follows (Fig. 1D): from stage 1 to stage 2, the perisperm undergoes significant growth, which determines the final size of the seed; at stage 3, the endosperm develops rapidly and replaces the perisperm in the locule; endosperm growth ends by stage 4 and oil starts to accumulate; stage 5 is characterised by endosperm hardening due to the massive deposition of galactomannans in cell walls; accumulation of reserves ends by stage 6, as illustrated by the transcription pattern of three genes representative of oil (OLE-1), protein (SSP1), and galactomannan (ManS1) storage (Fig. 1D), when the pericarp of the fruit turns yellow; fruit and seed maturity is completed at stage 7, when the pericarp becomes red
Using coffee seeds as a model, we searched for developmental processes that confer desiccation tolerance (DT) in orthodox seeds but that are lacking in intermediate seeds

Summary

Introduction

The seed is a key structure in the life cycle of higher plants; it the majority of flowering plants produce seeds that are able facilitates dispersal in space and over time, and to withstand almost complete loss of cellular water. Two other categories of seeds – intermediate and recalcitrant – have been defined with respect to their storability in gene banks (Roberts, 1973; Ellis et al, 1990) These terms are commonly used to describe the level of sensitivity to drying of non-orthodox seeds. Species of the genus Coffea vary considerably in the level of desiccation sensitivity of their seeds (Dussert et al, 2000), but neither the total lipid and fatty acid content of the endosperm (Dussert et al, 2001) nor the content of non-reducing sugars (Chabrillange et al, 2000) explain the interspecific variation in seed DT Since these early studies, no progress has been made in identifying the reasons for coffee seed sensitivity to drying, whereas their developmental features and the transcriptional programme for the accumulation of reserves are better understood (Joët et al, 2009, 2010, 2014). The roles of two TFs in sHSP accumulation were validated by Agrobacterium-mediated transformation of coffee somatic embryos, and changes in LEA transcript accumulation were further characterised by analysing the heat-stable proteome of mature seeds

Material and methods

Results

Discussion