Rosellinia necatrix infection induces differential gene expression between tolerant and susceptible avocado rootstocks.

Rosellinia necatrix is the causal agent of avocado white root rot (WRR). Control of this soil-borne disease is difficult, and the use of tolerant rootstocks may present an effective method to lessen its impact. To date, no studies on the molecular mechanisms regulating the avocado plant response towards this pathogen have been undertaken. To shed light on the mechanisms underpinning disease susceptibility and tolerance, molecular analysis of the gene's response in two avocado rootstocks with a contrasting disease reaction was assessed. Gene expression profiles against R. necatrix were carried out in the susceptible 'Dusa' and the tolerant selection BG83 avocado genotypes by micro-array analysis. In 'Dusa', the early response was mainly related to redox processes and cell-wall degradation activities, all becoming enhanced after disease progression affected photosynthetic capacity, whereas tolerance to R. necatrix in BG83 relied on the induction of protease inhibitors and their negative regulators, as well as genes related to tolerance to salt and osmotic stress such as aspartic peptidase domain-containing proteins and gdsl esterase lipase proteins. In addition, three protease inhibitors were identified, glu protease, trypsin and endopeptidase inhibitors, which were highly overexpressed in the tolerant genotype when compared to susceptible 'Dusa', after infection with R. necatrix, reaching fold change values of 52, 19 and 38, respectively. The contrasting results between 'Dusa' and BG83 provide new insights into the different mechanisms involved in avocado tolerance to Phytophthora cinnamomi and R. necatrix, which are consistent with their biotrophic and necrotrophic lifestyles, respectively. The differential induction of genes involved in salt and osmotic stress in BG83 could indicate that R. necatrix penetration into the roots is associated with osmotic effects, suggesting that BG83's tolerance to R. necatrix is related to the ability to withstand osmotic imbalance. In addition, the high expression of protease inhibitors in tolerant BG83 compared to susceptible 'Dusa' after infection with the pathogen suggests the important role that these proteins may play in the defence of avocado rootstocks against R. necatrix.

Transcriptomic time-series analysis of early development in olive from germinated embryos to juvenile tree.

BACKGROUND: Despite its relevance, almost no studies account for the genetic control in the early stages of tree development, i.e. from germination on. This study seeks to make a quite complete transcriptome for olive development and to elucidate the dynamic regulation of the transcriptomic response during the early-juvenile period by RNAseq time-series expression analysis. The transcriptome was made from 342,049,597 paired-end reads of 101 bp in length. The assembled transcriptome contained 109,125 unigenes (N50 = 1490 bp, average length = 839). RESULTS: The time-series-expression analysis showed that, embryonic structures present at the first month after the induction of germination reached a more differentiated state in two-month-old seedlings. Once the plants were between three and four months old and reached a size around 6-7 nodes, the first developmental stages appeared to be complete and the developing seedling became a juvenile plant. In addition, an AGL-gene was rapidly downregulated during the induction of germination. The repression of this gene was very strong, as evidenced by the low levels of gene expression during plant development from the embryonic seedling to undetectable levels of expression in the adult tree. These results suggest that this gene may be involved in seed dormancy and could be a repressor of the germination. Also, an APL1-like olive gene was found to be expressed at high levels during flowering, and was also expressed during the cold incubation in the activation of embryo germination, suggesting a probable role in embryonic development. CONCLUSIONS: The early development from germination to the juvenile stage of olive seedlings occurred when plants reached a size around 6-7 nodes, and general changes of relevant groups of genes involved in development are described. An AGL-gene was proposed to be involved in germination repression. An APL1-like gene was found to have a probable role in embryonic development.