Phylogenetic and Expression Analysis of the Sucrose Synthase and Sucrose Phosphate Synthase Gene Family in Potatoes.

Sucrose synthase (SUS) and sucrose phosphate synthase (SPS) are essential in plant sucrose metabolism. The potato is an important crop worldwide, but systematic analyses of the StSUS and StSPS gene families in potatoes are still lacking. Ten sucrose metabolism-related genes were identified in this study. The SUSs and SPSs could each be split into three subgroups through phylogenetic analysis. StSUSIc was the most highly expressed gene in different developmental tissues. Ka/Ks analysis showed that StSUSIb and StSUSIc were subjected to more-significant homozygous selection pressure. Our cis-acting element analysis of the StSUS and StSPS promoter sequences showed four elements: defense- and stress-responsive, hormone-responsive, light-responsive, and transcription factor elements. The expression of StSUS and StSPS genes was found to be regulated by circadian rhythm. In the treatments of 1% to 5% sucrose, glucose, and fructose, the expression of StSUS and StSPS family genes was enhanced by sucrose, but inhibited at high-glucose and fructose concentrations. This study identified six StSUS and four StSPS genes and analyzed their gene structure, conserved motifs, chromosome position, promoter elements, phylogenetic tree, and tissue-specific expression patterns. Our results will motivate more research into the biological process underlying the genes of sucrose metabolism in potatoes.

Different epitopes of Ralstonia solanacearum effector RipAW are recognized by two Nicotiana species and trigger immune responses.

Diverse pathogen effectors convergently target conserved components in plant immunity guarded by intracellular nucleotide-binding domain leucine-rich repeat receptors (NLRs) and activate effector-triggered immunity (ETI), often causing cell death. Little is known of the differences underlying ETI in different plants triggered by the same effector. In this study, we demonstrated that effector RipAW triggers ETI on Nicotiana benthamiana and Nicotiana tabacum. Both the first 107 amino acids (N1-107 ) and RipAW E3-ligase activity are required but not sufficient for triggering ETI on N. benthamiana. However, on N. tabacum, the N1-107 fragment is essential and sufficient for inducing cell death. The first 60 amino acids of the protein are not essential for RipAW-triggered cell death on either N. benthamiana or N. tabacum. Furthermore, simultaneous mutation of both R75 and R78 disrupts RipAW-triggered ETI on N. tabacum, but not on N. benthamiana. In addition, N. tabacum recognizes more RipAW orthologs than N. benthamiana. These data showcase the commonalities and specificities of RipAW-activated ETI in two evolutionally related species, suggesting Nicotiana species have acquired different abilities to perceive RipAW and activate plant defences during plant-pathogen co-evolution.

A quick and efficient hydroponic potato infection method for evaluating potato resistance and Ralstonia solanacearum virulence.

BACKGROUND: Potato, the third most important crop worldwide, plays a critical role in human food security. Brown rot, one of the most destructive potato diseases caused by Ralstonia solanacearum, results in huge economic losses every year. A quick, stable, low cost and high throughout method is required to meet the demands of identification of germplasm resistance to bacterial wilt in potato breeding programs. RESULTS: Here we present a novel R. solanacearum hydroponic infection assay on potato plants grown in vitro. Through testing wilt symptom appearance and bacterial colonization in aerial part of plants, we found that the optimum conditions for in vitro potato infection were using an OD600 0.01 bacterial solution suspended with tap water for infection, broken potato roots and an open container. Infection using R. solanacearum strains with differential degree of aggressivity demonstrated that this infection system is equally efficient as soil-drench inoculation for assessment of R. solanacearum virulence on potato. A small-scale assessment of 32 potato germplasms identified three varieties highly resistant to the pathogen, which indicates this infection system is a useful method for high-throughout screening of potato germplasm for resistance. Furthermore, we demonstrate the utility of a strain carrying luminescence to easily quantify bacterial colonization and the detection of latent infections in hydroponic conditions, which can be efficiently used in potato breeding programs. CONCLUSIONS: We have established a quick and efficient in vitro potato infection system, which may facilitate breeding for new potato cultivars with high resistance to R. solanacearum.

Deep Sequencing Reveals Early Reprogramming of Arabidopsis Root Transcriptomes Upon Ralstonia solanacearum Infection.

Bacterial wilt caused by the bacterial pathogen Ralstonia solanacearum is one of the most devastating crop diseases worldwide. The molecular mechanisms controlling the early stage of R. solanacearum colonization in the root remain unknown. Aiming to better understand the mechanism of the establishment of R. solanacearum infection in root, we established four stages in the early interaction of the pathogen with Arabidopsis roots and determined the transcriptional profiles of these stages of infection. A total 2,698 genes were identified as differentially expressed genes during the initial 96 h after infection, with the majority of changes in gene expression occurring after pathogen-triggered root-hair development observed. Further analysis of differentially expressed genes indicated sequential activation of multiple hormone signaling cascades, including abscisic acid (ABA), auxin, jasmonic acid, and ethylene. Simultaneous impairment of ABA receptor genes promoted plant wilting symptoms after R. solanacearum infection but did not affect primary root growth inhibition or root-hair and lateral root formation caused by R. solanacearum. This indicated that ABA signaling positively regulates root defense to R. solanacearum. Moreover, transcriptional changes of genes involved in primary root, lateral root, and root-hair formation exhibited high temporal dynamics upon infection. Taken together, our results suggest that successful infection of R. solanacearum on roots is a highly programmed process involving in hormone crosstalk.