Functional analysis of Lecrk-a1, a lectin receptor kinase involved in pathogen resistance

β-aminobutyric acid (BABA) 是一種人工合成的氨基酸。已知經過BABA處理的植物在面對生物或非生物性逆境時可以展現較快且較強的防禦能力，但目前仍未完全明瞭BABA在植物中的的作用機制。 本論文研究篩檢到一突變種，其對於BABA的反應異於野生種，BABA在此突變種失去了提供保護的效果， 表示此突變的基因可能參與BABA在植物中的訊息傳導路徑。此突變種是利用農桿菌的T-DNA插入阿拉伯芥染色體方式得到的，被插入而破壞的是一屬於凝集素a1家族的基因LecRK- a1. LecRK- a1的突變種對於活體寄生型病原菌(biotrophic)和死體寄生型病原菌(necrotrophic)展現相異的抵抗力。此突變種對於 Botrytis cinerea的抵抗力降低，而對於 Pseudomonas syringae pv. tomato DC3000的抵抗力提高（根據CFU和PR1基因的表現而非感染症狀）。這些性狀可能是因為在受不同病原菌感染後， 突變種分別有較低的PDF1.2基因表現和較高的PR-1基因表現所導致。 另外在沒有任何處理的狀況下， 此突變種已展現較野生種高的 PR-1, PR-2, PR-5 基因表現, 表示其體中的SA防禦機制已處在活化的狀態；另一方面,突變種中的 PDF1.2 ，VSP1, LOX2基因表現較低， 表示其JA/ET防禦機制受到抑制.另外在SA防禦機制方面, 野生種中的 PR-1基因表現會隨著植物的成長而昇高， 不過會於植株約四週大時停止上昇， 但是在突變種中的PR-1基因表現即使植株超過六週大仍會持續上昇。 此突變基因之互補試驗的資料顯示是此基因突變造成突變種的高 PR-1基因表現以及對Botrytis cinerea的低抵抗力。β-aminobutyric acid (BABA) is an artificial, non-protein amino acid. BABA-treated plants mount a faster and stronger resistance against biotic and abiotic stress. However, the mode of action of BABA is poorly understood. Through a reverse genetic approach, we discovered the lecrk-a1 mutant that showed an altered response to BABA, including loss of BABA-mediated protection, indicating that this gene could be involved in BABA signalling pathway. This knockout lecrk-a1 mutant possesses a T-DNA insertion in the kinase domain of the lectin receptor-like kinase a1 gene (LecRK-a1). Inactivation of LecRK-a1 causes distinct responses to biotrophic and necrotrophic pathogens. lecrk-a1 was more susceptible to Botrytis cinerea and more resistant to Pseudomonas syringae pv. tomato DC3000, possibly due to lower PDF1.2 and higher PR-1 expression after pathogen inoculation, respectively. Without any treatment, lecrk-a1 demonstrated high SA-related PR-1, PR-2 and PR-5 gene expressions. On the other hand, expression of PDF1.2 gene and other secondary JA/ET marker genes was low in lecrk-a1. Together, it suggests that the SA-defense response is constitutively activated and the JA/ET signaling is reduced in the lecrk-a1. The PR-1 expression strongly increases as the lecrk-a1 ages, while in wild type Col-0, increase in PR-1 expression is arrested at 4 weeks after germination. LecRK-a1 might be involved in age-related resistance. Introducing a wild type copy of the LecRK-a1 coding sequence in the lecrk-a1 background restored a normal PR-1 gene expression and the susceptibility to B. cinerea, confirming that the observed phenotypes are caused by a mutation in LecRK-a1