lignin-down-regulation-zea-mays-via-dsrnai-klason-lignin

Lignin Down-regulation of <em>Zea mays</em> via dsRNAi and Klason Lignin Analysis

To facilitate the use of lignocellulosic biomass as an alternative bioenergy resource, during biological conversion processes, a pretreatment step is ...

The Institute for Advanced Learning and Research

Salicylic acid (SA) is a key endogenous signal that mediates defense gene expression and disease resistance in many dicotyledonous species. In contrast to tobacco and Arabidopsis, which contain low basal levels of SA, rice has two orders of magnitude higher levels of SA and appears to be insensitive to exogenous SA treatment. To determine the role of SA in rice plants, we have generated SA-deficient transgenic rice by expressing the bacterial salicylate hydroxylase that degrades SA. Depletion of high levels of endogenous SA in transgenic rice does not measurably affect defense gene expression, but reduces the plant's capacity to detoxify reactive oxygen intermediates (ROI). SA-deficient transgenic rice contains elevated levels of superoxide and H2O2, and exhibits spontaneous lesion formation in an age- and light-dependent manner. Exogenous application of SA analog benzothiadiazole complements SA deficiency and suppresses ROI levels and lesion formation. Although an increase of conjugated catechol was detected in SA-deficient rice, catechol does not appear to significantly affect ROI levels based on the endogenous catechol data and exogenous catechol treatment. When infected with the blast fungus (Magnaporthe grisea), SA-deficient rice exhibits increased susceptibility to oxidative bursts elicited by avirulent isolates. Furthermore, SA-deficient rice is hyperresponsive to oxidative damage caused by paraquat treatment. Taken together, our results strongly suggest that SA plays an important role to modulate redox balance and protect rice plants from oxidative stress.

Endogenous salicylic acid protects rice plants from oxidative damage caused by aging as well as biotic and abiotic stress.

Many studies in dicotyledonous plants have shown that jasmonates, including jasmonic acid (JA) and methyl jasmonate, are important signal molecules involved in induced resistance to pathogen infection and insect herbivory. However, very little genetic and molecular evidence is available to demonstrate their role in host defense response of rice and other economically important monocot plants. In this study, we have shown that exogenous application of JA was able to activate defense gene expression and local induced resistance in rice seedlings against the rice blast fungus (Magnaporthe grisea). Furthermore, we have characterized a pathogen-inducible rice OsAOS2 gene (which encodes allene oxide synthase, a key enzyme in the JA biosynthetic pathway) and examined the role of endogenous JA in rice defense response through transgenic manipulation of the JA biosynthesis. Sequence analysis indicated that OsAOS2 contains four common domains of the cytochrome P450 enzyme, but does not have the signal peptide for chloroplast targeting. The basal level of OsAOS2 expression is very low in leaves but relatively high in the sheath, culm, and flower of rice plants. Interestingly, the expression of OsAOS2 in rice leaves can be induced significantly upon M. grisea infection. Transgenic rice lines carrying the OsAOS2 transgene under the control of a strong, pathogen-inducible PBZ1 promoter accumulated abundant OsAOS2 transcripts and higher levels of JA, especially after the pathogen infection. These transgenic lines also exhibited enhanced activation of pathogenesis-related (PR) genes such as PR1a, PR3, and PR5 and increased resistance to M. grisea infection. Our results suggest that JA plays a significant role in PR gene induction and blast resistance in rice plants.

Inducible overexpression of a rice allene oxide synthase gene increases the endogenous jasmonic acid level, PR gene expression, and host resistance to fungal infection.

The RNA interference (RNAi) technique is a powerful tool to suppress gene expression and has been widely used for functional discovery of eukaryotic genes. To dissect defense-signaling pathways in rice, it is important to generate a series of rice mutant lines deficient in or insensitive to major signal molecules such as jasmonic acid and ethylene. Here we describe an RNAi protocol for generating and characterizing transgenic gene-silencing lines defective in rice jasmonic acid signaling. The RNAi technique should be useful for effective suppression of host genes encoding signaling components and facilitating the dissection of defense signal pathways in rice.

Use of RNA interference to dissect defense-signaling pathways in rice.

Endophytes are microorganisms that live within host plants for at least part of their life and do not cause apparent symptoms of diseases. In general, beneficial endophytes promote host plant growth, increase plant nutrient uptake, inhibit plant pathogen growth, reduce disease severity, and enhance tolerance to environmental stresses. As sustainable and renewable agricultural production (including current biofuel and bioenergy crops) increases in prominence, endophytic microorganisms will play important roles and offer environmentally-friendly methods to increase productivity while reducing chemical inputs. This review discusses various aspects of beneficial fungal and bacterial endophyte interactions with plants, including the physiological and molecular mechanisms by which they benefit plant performance. We also discuss the potential for genetic modification of endophytes with useful genes, which could be used to impart additional traits following inoculation with the genetically engineered endophytes. Finally, we review US-issued patents over the past decade which relate to the use of fungal and bacterial endophytes for plant growth and stress tolerance improvement.

The use of beneficial microbial endophytes for plant biomass and stress tolerance improvement.

Switchgrass is one of the most promising bioenergy crop candidates for the US. It gives relatively high biomass yield and can grow on marginal lands. However, its yields vary from year to year and from location to location. Thus it is imperative to develop a low input and sustainable switchgrass feedstock production system. One of the most feasible ways to increase biomass yields is to harness benefits of microbial endophytes.

Article	Year
Endogenous salicylic acid protects rice plants from oxidative damage caused by aging as well as biotic and abiotic stress. The Plant journal : for cell and molecular biology\| PubMed ID: 15584956	2004
Inducible overexpression of a rice allene oxide synthase gene increases the endogenous jasmonic acid level, PR gene expression, and host resistance to fungal infection. Molecular plant-microbe interactions : MPMI\| PubMed ID: 17022177	2006
Use of RNA interference to dissect defense-signaling pathways in rice. Methods in molecular biology (Clifton, N.J.)\| PubMed ID: 17172753	2007
The use of beneficial microbial endophytes for plant biomass and stress tolerance improvement. Recent patents on biotechnology\| PubMed ID: 20201804	2010
Growth promotion and colonization of switchgrass (Panicum virgatum) cv. Alamo by bacterial endophyte Burkholderia phytofirmans strain PsJN. Biotechnology for biofuels\| PubMed ID: 22647367	2012

Chuansheng Mei

Biography

JoVE Journal Publications

Other Publications