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Arabinogalactan proteins (AGPs) are members of a family of proteins that play important roles in cell wall dynamics. AGPs from inclined pines were determined using JIM7, LM2, and LM6 antibodies, showing a higher concentration in one side of the stem. The accumulation of AGPs in xylem and cell wall tissues is enhanced in response to loss of tree stem verticality. The differential gene expression of AGPs indicates that these proteins could be involved in the early response to inclination and also trigger signals such as lignin accumulation, as well as thicken cell wall and lamella media to restore stem vertical growth. A subfamily member of AGPs, which is Fasciclin-like has been described in angiosperm species as inducing tension wood and in some gymnosperms. A search for gene sequences of this subfamily was performed on an RNA-seq library, where 12 sequences were identified containing one or two fasciclin I domains (FAS), named PrFLA1 to PrFLA12. Four of these sequences were phylogenetically classified in group A, where PrFLA1 and PrFLA4 are differentially expressed in tilted pine trees.

The molecular mechanisms underlying inclination responses in trees are unclear. In this study, we identified a MADS-box transcription factor differentially expressed early after inclination in the stems of Pinus radiata D. Don. PrMADS10 has a CDS of 582 bp and encodes a group II MADS-box transcription factor. We measured highest accumulation of this transcript on the lower side of inclined pine stems. In an effort to identify putative targets, we stably transformed Arabidopsis thaliana with a 35S::PrMADS10 construct. Transcriptome analysis revealed 1,219 genes differentially-expressed, with 690 and 529 genes up- and down-regulated respectively, when comparing the transgenic and wild-type. Differentially-expressed genes belong to different biological processes, but were enriched in cell wall remodeling and phenylpropanoid metabolic functions. Interestingly, lignin content was 30% higher in transgenic as compared to wild-type plants consistent with observed changes in gene expression. Differentially expressed transcription factors and phenylpropanoid genes were analyzed using STRING. Several MYB and NAC transcription factors showed interactions with genes of the phenylpropanoid pathway. Together, these results implicate PrMADS10 as a regulatory factor, triggering the expression of other transcription factors and genes involved in the synthesis of lignin.

Peaches and nectarines are frequently attacked by the green peach aphid Myzus persicae (Sulzer), with significant negative impacts on fruit production. The genetic variability of resistance to this aphid among commercial cultivars of Prunus persica (L) Batsch and Prunus persica variety nectarina was evaluated in this study. In total, 16 cultivars of P. persica were selected to evaluate the occurrence and population growth rate of M. persicae in commercial orchards, as well as in no-choice and probing behavior laboratory assays. The results showed variability between cultivars in resistance and susceptibility to M. persicae, with three cultivars exhibiting different signatures of resistance. The peach cultivar ‘Elegant Lady’ exhibited a low occurrence of aphids in the orchard, a low rate of growth, moderate leaf-rejection in a no-choice test and a higher number and longer period of salivation into sieve elements, suggesting resistance at the phloematic level. The nectarine cultivar ‘August Red’ also exhibited low aphid occurrence in the orchard, a low rate of growth, and resistance at the prephloem and phloem levels. Finally, the nectarine ‘July Red-NS92’ exhibited a low occurrence of aphids in the orchard, a higher number of rejections in no-choice assays and no ingestion of phloem during the probing behavior experiments, suggesting prephloematic resistance. The rest of the cultivars studied exhibited clear susceptibility. Hence, different resistance mechanisms are apparent among the studied cultivars. The information gathered in this study regarding the resistance to M. persicae may assist breeding programs aimed at increasing aphid resistance to peaches and nectarines.