Systemic acquired resistance (SAR) is an inducible defense response that protects plants against a broad spectrum of pathogens. A central regulator of SAR in Arabidopsis is NPR1 (nonexpresser of pathogenesis-related genes). In rice, overexpression of Arabidopsis NPR1 enhances plant resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae. This report demonstrates that overexpression of (At)NPR1 in rice also triggers a lesion-mimic/cell death (LMD) phenotype. The LMD phenotype is environmentally regulated and heritable. In addition, the development of lesions and death correlates with the expression of rice defense genes and the accumulation of hydrogen peroxide. Application of the salicylic acid (SA) analog, benzo(1,2,3) thiadiazole-7-carbothioc acid S-methyl ester (BTH), potentiates this phenotype Endogenous SA levels are reduced in rice overexpressing (At)NPR1 when compared with wildtype plants, supporting the idea that (At)NPR1 may perceive and modulate the accumulation of SA. The association of (At)NPR1 expression in rice with the development of an LMD phenotype suggests that (At)NPR1 has multiple roles in plant stress responses that may affect its efficacy as a transgenic tool for engineering broad-spectrum resistance.

Summary In tobacco and other Solanaceae species, the tobacco N gene confers resistance to tobacco mosaic virus (TMV), and leads to induction of standard defense and resistance responses. Here, we report the use of N‐transgenic tomato to identify a fast‐neutron mutant, sun1‐1 (suppressor of N), that is defective in N‐mediated resistance. Induction of salicylic acid (SA) and expression of pathogenesis‐related (PR) genes, each signatures of systemic acquired resistance, are both dramatically suppressed in sun1‐1 plants after TMV treatment compared to wild‐type plants. Application of exogenous SA restores PR gene expression, indicating that SUN1 acts upstream of SA. Upon challenge with additional pathogens, we found that the sun1‐1 mutation impairs resistance mediated by certain resistance (R) genes, (Bs4, I, and Ve), but not others (Mi‐1). In addition, sun1‐1 plants exhibit enhanced susceptibility to TMV, as well as to virulent pathogens. sun1‐1 has been identified as an EDS1 homolog present on chromosome 6 of tomato. The discovery of enhanced susceptibility in the sun1‐1 (Le_eds1‐1) mutant plant, which contrasts to reports in Nicotiana benthamiana using virus‐induced gene silencing, provides evidence that the intersection of R gene‐mediated pathways with general resistance pathways is conserved in a Solanaceous species. In tomato, EDS1 is important for mediating resistance to a broad range of pathogens (viral, bacterial, and fungal pathogens), yet shows specificity in the class of R genes that it affects (TIR‐NBS‐LRR as opposed to CC‐NBS‐LRR). In addition, a requirement for EDS1 for Ve‐mediated resistance in tomato exposes that the receptor‐like R gene class may also require EDS1.

Vitamin B6 is one of the most versatile cofactors in plants and an essential phytonutrient in the human diet that benefits a variety of human health aspects. Although biosynthesis of the vitamin has been well resolved in recent years, the main research is currently based on Arabidopsis thaliana with very little work done on major crop plants. Here we provide the first report on interactions and expression profiles of PDX genes for vitamin B6 biosynthesis in potato and how vitamin B6 content varies in tubers of different genotypes. The results demonstrate that potato is an excellent resource for this vitamin and that strong natural variation in vitamin B6 content among the tested cultivars indicates high potential to fortify vitamin B6 nutrition in potato-based foods.

This chapter focuses on the growth and development of S. tuberosum under commercial production and describes how potato plant morphology changes as plants grow and develop. To simplify the discussion on potato development, the chapter is separated into a logical series of growth and developmental stages including propagation, seed tuber dormancy and physiological age, tuber anatomy and sprout development, tuber initiation, canopy development, tuber bulking, and plant and tuber maturation.

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