Functional Analysis of the Arabidopsis PAL Gene Family in Plant Growth, Development, and Response to Environmental Stress    

Abstract

Phenylalanine ammonia-lyase (PAL) catalyzes the first step of the phenylpropanoid pathway, which produces precursors to a variety of important secondary metabolites. Arabidopsis (Arabidopsis thaliana) contains four PAL genes (PAL1-PAL4), but there has been no genetic analysis to assess the biological functions of the entire gene family. Here, we report the generation and analysis of combined mutations for the four Arabidopsis PAL genes. Contrary to a previous report, we found that three independent pal1 pal2 double mutants were fertile and generated yellow seeds due to the lack of condensed tannin pigments in the seed coat. The pal1 pal2 double mutants were also deficient in anthocyanin pigments in various plant tissues, which accumulate in wild-type plants under stress conditions. Thus, PAL1 and PAL2 have a redundant role in flavonoid biosynthesis. Furthermore, the pal1 pal2 double mutants were more sensitive to ultraviolet-B light but more tolerant to drought than wildtype plants. We have also generated two independent pal1 pal2 pal3 pal4 quadruple knockout mutants, which are stunted and sterile. The quadruple knockout mutants still contained about 10% of the wild-type PAL activity, which might result from one or more leaky pal mutant genes or from other unknown PAL genes. The quadruple mutants also accumulated substantially reduced levels of salicylic acid and displayed increased susceptibility to a virulent strain of the bacterial pathogen Pseudomonas syringae. These results provide further evidence for both distinct and overlapping roles of the Arabidopsis PAL genes in plant growth, development, and responses to environmental stresses.

Soybean Homologs of MPK4 Negatively Regulate Defense Responses and Positively Regulate Growth and Development

“…Unexpectedly, we found that the transcripts of ICS1 (Glyma01g25690) were repressed by 8-fold in GmMPK4-silenced plants. This suggests that the overaccumulation of SA in GmMPK4-silenced plants occurs in an ICS1-independent manner, possibly from precursors derived from the PAL pathway (Ribnicky et al, 1998;Huang et al, 2010), which would be consistent with the induction of genes encoding PALs. Alternatively, SA production is GmICS1 dependent, but GmICS1 expression is under negative feedback regulation by its own product, SA.…”

Differential Expression of Phenylalanine Ammonia-Lyase in Different Tissues of Sugarcane (Saccharum officinarum L.) during Development

“…PAL is an indication of higher production of other secondary metabolites for resistance to pathogenesis and environmental stress (Huang et al 2010). It has been found that flavonoids and other phenolic compounds inhibit pathogens ranging from bacteria to fungi and insects (Hassan and Mathesius 2012).…”

“…Previous researchers have recognized the contribution and control of PAL expression during the development of Arabidopsis, bamboo, olive, kenaf, and melon (Diallinas and Kanellis 1994;Ortega-García et al 2009;Huang et al 2010;Gao et al 2012;Jeong et al 2012).…”

“…Phenylalanine ammonia-lyase (EC 4.3.1.5) catalyzes the deamination of Lphenylalanine to yield trans-cinnamic acid and NH 4 , which is the first step of the phenylpropanoid pathway (Huang et al 2010). Secondary metabolites produced from the phenylpropanoid pathway include the cell wall structural polymer, lignin, flavonoids, UV protectants, wound protectants, isoflavonoid and furano coumarin phytoalexin antibiotics (Ozeki et al 2000;Ludwikow and Sadowski 2008;Hyun et al 2011).…”

Arabidopsis Kelch Repeat F-Box Proteins Regulate Phenylpropanoid Biosynthesis via Controlling the Turnover of Phenylalanine Ammonia-Lyase

“…PAL is a tetrameric enzyme; in most species, its subunits are encoded by a small multigene family (Cramer et al, 1989;Wanner et al, 1995). Arabidopsis has four PAL members (Wanner et al, 1995;Raes et al, 2003): Three (PAL1, PAL2, and PAL4) exhibit a high binding affinity for Phe and are associated with both the soluble phenolic and tissuespecific lignin synthesis (Rohde et al, 2004;Huang et al, 2010). By contrast, PAL3 has much lower in vitro catalytic efficacy than the other three isozymes and its biological function remains unclear (Cochrane et al, 2004).…”