Circadian rhythm and redox homeostasis candidate genes showed association with shallow elevation in Norway spruce.

The analysis of genetic variation underlying local adaptation in natural populations, together with the response to different external stimuli, is currently a hot topic in forest sciences, with the aim of identifying genetic markers controlling key phenotypic traits of interest for their inclusion in restoration and breeding programs. In Europe, one of the main tree species is Norway spruce (Picea abies (L.) H.Karst.). Using the MassARRAY® platform, 568 trees from North Rhine-Westphalia (Germany) were genotyped with 94 single nucleotide polymorphisms (SNPs) related to circadian and growth rhythms, and to stress response. The association analysis of the selected markers with health status and elevation was performed using three different methods, and those identified by at least two of these were considered as high confidence associated SNPs. While just five markers showed a weak association with health condition, 32 SNPs were correlated with elevation, six of which were considered as high confidence associated SNPs, as indicated by at least two different association methods. Among these genes, thioredoxin and pseudo response regulator 1 (PRR1) are involved in redox homeostasis and ROS detoxification, APETALA2-like 3 (AP2L3), a transcription factor, is involved in seasonal apical growth, and a RPS2-like is a disease resistance gene. The function of some of these genes in controlling light-dependent reactions and metabolic processes suggests signatures of adaptation to local photoperiod and the synchronization of the circadian rhythm. This work provides new insights into the genetic basis of local adaptation over a shallow elevation gradient in Norway spruce.

Wood development regulators involved in apical growth in Pinus canariensis.

The shoot apical meristem is responsible of seasonal length increase in plants. In woody plants transition from primary to secondary growth is also produced during seasonal apical growth. These processes are controlled by different families of transcription factors. Levels of transcriptomic activity during apical growth were measured by means of a cDNA microarray designed from sequences related to meristematic activity in Pinus canariensis. The identification of differentially expressed genes was performed using a time-course analysis. A total of 7170 genes were differentially expressed and grouped in six clusters according to their expression profiles. We identified master regulators, such as WUSCHEL-like HOMEOBOX (WOX), to be involved in the first stages of apical development, i.e. growth of primary tissues, while other transcription factors, such as Class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) and KNOTTED-like (KNOX) and BEL1-like (BELL) HOMEODOMAIN proteins, were found to be induced during last stages of apical seasonal development, already with secondary growth. Our results reveal the main expression patterns of these genes during apical development and the transition from primary to secondary stem growth. In particular, the regulatory factors identified play key roles in controlling stem architecture and constitute candidate genes for the study of other development processes in conifers.

Transcriptomic analysis of wound xylem formation in Pinus canariensis.

BACKGROUND: Woody plants, especially trees, usually must face several injuries caused by different agents during their lives. Healing of injuries in stem and branches, affecting the vascular cambium and xylem can take several years. In conifers, healing takes place mainly from the remaining vascular cambium in the margin of the wound. The woundwood formed in conifers during healing usually presents malformed and disordered tracheids as well as abundant traumatic resin ducts. These characteristics affect its functionality as water conductor and its technological properties. RESULTS: In this work we analyze for the first time the transcriptomic basis of the formation of traumatic wood in conifers, and reveal some differences with normal early- and late-wood. Microarray analysis of the differentiating traumatic wood, confirmed by quantitative RT-PCR, has revealed alterations in the transcription profile of up to 1408 genes during the first period of healing. We have grouped these genes in twelve clusters, according to their transcription profiles, and have distinguished accordingly two main phases during this first healing. CONCLUSIONS: Wounding induces a complete rearrangement of the transcriptional program in the cambial zone close to the injuries. At the first instance, radial growth is stopped, and a complete set of defensive genes, mostly related to biotic stress, are induced. Later on, cambial activity is restored in the lateral borders of the wound, even at a high rate. During this second stage certain genes related to early-wood formation, including genes involved in cell wall formation and transcription factors, are significantly overexpressed, while certain late-wood related genes are repressed. Additionally, significant alterations in the transcription profile of abundant non annotated genes are reported.